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Inge Lehmann Medal

Information on the Lehmann Medal

The Inge Lehmann Medal is given annually to a senior scientist in recognition of outstanding contributions to the understanding of the structure, composition, and dynamics of the Earth’s mantle and core. Recipients of this award typically conduct research in the following disciplines: geomagnetism, paleomagnetism and electromagnetism, mineral rock physics, seismology, study of the Earth’s deep interior, and tectonophysics.

The Lehmann Medal is named in honor of Inge Lehmann, who made many contributions to our understanding of the Earth’s deep interior, including her discovery of the Earth’s inner core in 1936.  Lehmann served for 25 years as the first chief of the seismology department of the Royal Danish Geodetic Institute and was a former president of the European Seismological Federation, the Danish Geophysical Society, and vice president of the International Association of Seismology and Physics of the Earth’s Interior.

Earth cross section showing its internal structure. Digital illustration.

Award benefits

AGU is proud to recognize our honorees. Recipients of the Inge Lehmann Medal will receive an engraved medal, as well as the following benefits with the honor:

  • 1
    Awardee will be made an AGU Fellow (if the honoree has been an AGU member for three consecutive years and is not already a Fellow)
  • 2
    Recognition in Eos
  • 3
    Recognition at the AGU Fall Meeting during the award presentation year
  • 4
    Four complimentary hotel nights at the AGU Fall Meeting during the award presentation year
  • 5
    Two complimentary tickets to the Honors Banquet at the AGU Fall Meeting during the award presentation year


To better understand eligibility for nominators, supporters and committee members, review AGU’s Honors Conflict of Interest Policy.

  • 1

    Nominees: The nominee should be a senior scientist, but is not required to be an active AGU member. They should be in compliance with the Conflict of Interest Policy.

  • 2

    Nominators: Nominators must be active AGU members and in compliance with the Conflict of Interest Policy. Duplicate nominations for the same individual will not be accepted. However, one co-nominator is permitted (but not required) per nomination.

  • 3

    Supporters: Individuals who write letters of support for the nominee are not required to be active AGU members but must be in compliance with the Conflict of Interest Policy.

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Nomination package

Your nomination package must contain all of the following files, which should be no more than two pages in length per document. For detailed information on the requirements, review the Union Awards, Medals and Prizes Frequently Asked Questions.

  • A nomination letter with one-sentence citation (150 characters or less). Letterhead stationery is preferred. Nominator’s name, title, institution, and contact information are required. The citation should appear at either the beginning or end of the nomination letter.
  • A curriculum vitae for the nominee. Include the candidate’s name, address and email, history of employment, degrees, research experience, honors, memberships, and service to the community through committee work, advisory boards, etc.
  • A selected bibliography stating the total number, the types of publications and the number published by AGU.
  • Three letters of support not including the nomination letter. Letterhead is preferred. Supporter’s name, title, institution, and contact information are required.

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Past recipients

Peter M Shearer


Ulrich Christensen was awarded the 2019 Inge Lehmann Medal at the AGU Fall Meeting Honors Ceremony, held on 11 December 2019 in San Francisco, Calif. The medal is for “contributions to the understanding of the structure, composition, and dynamics of the Earth’s mantle and core.”



Uli Christensen is one of the unique individuals who have contributed to both domains of core and mantle and as such is a fitting recipient of the Lehmann Medal. It is rare for an individual to have had such a level of impact in both domains of geodynamo theory and geodynamics.

Early in his career, in joint work with David Yuen, Uli was the first to determine how pressure-induced phase changes influence mantle convection, demonstrating the viability of circulation across the mantle transition zone.

With Al Hofmann in 1994 he showed how gravitational segregation of ocean crust in the deep mantle resolves isotopic patterns observed in mantle-derived rocks.

Beginning in the late 1990s, Uli has produced a whole host of results that have clarified the behavior of numerical dynamo solutions; along the way he has shown great leadership in the geomagnetism community by instigating the first dynamo benchmark exercise, and he has engaged with observationalists for the common advancement of the subject.

Of the pivotal contributions made by Uli, I will highlight a select few. Uli is the originator of the mapping of regime boundaries for convective dynamos as a function of control parameters such as the Rayleigh, Ekman, and magnetic Prandtl numbers. Further work illuminated the regime boundary between dipolar and nondipolar dynamos, attributed to be controlled by the local Rossby number.

A lasting legacy is work with J. Aubert to create a comprehensive scaling theory for the geodynamo. This showed how the velocities, heat transfer, and magnetic field strengths all scale with the convective power. This analysis was groundbreaking when it was introduced 13 years ago and remains at the very forefront of modern ideas of the geodynamo. A tremendous application of these ideas was to explain the magnetic fields of planets and stars.

Uli has become a much-sought-after keynote speaker at conferences as a result of his prominence in the subject and broad knowledge of the area. It should be mentioned that Uli has freely shared his numerical dynamo database with others so that they can carry out their own analyses. This approach has won him many friends. He is a fitting recipient of AGU’s Lehmann Medal.

—Andy Jackson, ETH Zurich, Zurich, Switzerland


Thank you, Andy, for your kind words, and thank you to all who conspired to get me this prestigious medal. I was fortunate to be born at the right time. A law made by the German government when I was 17 provided generous support to students from low-income families, which allowed me to enter university. In the late 1970s, plate tectonics had come of age as an empirical theory, but its mechanism was not well understood. At the same time, computers became powerful enough for simulating complex nonlinear systems. Both fascinated me. My Ph.D. adviser was not an expert on either topic but was a very open-minded man. I was lucky that he gave me a free hand for working on the numerical simulation of mantle convection on my own. As a postdoc coming from the still somewhat parochial German geoscience community, Dave Yuen taught me, aside from a strong vocabulary in the English language, also the bold American way of tackling cutting-edge problems. Al Hofmann was so kind to host in his geochemistry department a guy who had not the vaguest idea about mantle isotopes. When I had mastered the fundamentals after 10 years, we published a paper together, marrying mantle convection with isotope modeling. In the late 1990s, I looked for something to give my research a new twist. I was lucky again—realistic geodynamo modeling had just become practical. Gary Glatzmaier generously shared his code, and Peter Olson initiated me, coming from the very sticky world of mantle convection, to the airy physics of rotating magnetohydrodynamics. I also profited a lot from working with other colleagues, postdocs, and students. From Neil Ribe I learned that nice numerical models are most useful when coupled with a scaling theory that allows us to extrapolate them to the real world. Carsten Kutzner and I made the first steps toward understanding when a dynamo produces a dipole-dominated field. With Julien Aubert I tackled the question of what actually controls the strength of the magnetic field. I tried to reach for the stars with astrophysicist Ansgar Reiners by showing that the magnetic fields of planets and those of rapidly rotating low-mass stars follow the same scaling rule. It was a great pleasure to collaborate with all these people and many more. I owe them tremendously, and without them my scientific career would certainly not have culminated in receiving the Inge Lehmann Medal.

—Ulrich Christensen, Max Planck Institute for Solar System Research, Göttingen, Germany

Yoshio Fukao was awarded the 2018 Inge Lehmann Medal at the AGU Fall Meeting Honors Ceremony, held on 12 December 2018 in Washington, D. C. The medal is for “contributions to the understanding of the structure, composition, and dynamics of the Earth’s mantle and core.”



Yoshio Fukao is a deep thinker with influential ideas who has made outstanding observational and theoretical contributions to solid Earth geophysics using seismological tools.

He has been a leader on imaging of subducted slabs in the mantle transition zone. His interest in processes related to subduction started with the characterization of the sources of large and, in particular, deep earthquakes. Later, he clarified the depth extent of subducted oceanic basaltic crust before its transformation to eclogite, thus providing insights on the physical conditions in the slab down to ~60 kilometer (km) depth. In the 1990s, he showed two classes of behavior of slabs around the world: those that lie horizontally above the 660-km discontinuity, which he coined “stagnant slabs,” and those that penetrate deeper and are not as directly connected to present-day subduction. This showed that the Earth’s mantle is in an intermediate state between two highly debated dynamic extremes: one-layer and two-layer convection. Recently, analysis of the latest high-resolution P wave global model developed with former student Masayuki Obayashi led them to demonstrate that most slabs either stagnate above 660 km or flatten out deeper, around 1,000 km depth. These results have turned the attention of the community to a possible rheological boundary around 1,000 km depth and have inspired further studies in geodynamics and mineral physics, aiming at understanding the nature and significance of this potential redefinition of an extended transition zone.

Yoshio Fukao has also worked extensively on Earth’s free oscillations and contributed to another important discovery: that of the presence, in the absence of earthquakes, of a low-frequency “hum” continuously excited by sources in the oceans and/or the atmosphere, which, when applied to planets without earthquakes, may provide a powerful way to study their internal structure.

He has been an exceptional mentor to younger scientists. He has also been a leader in the establishment of research infrastructure in Japan, such as the “Earth simulator” and the Institute for Frontier Research on Earth Evolution, and has been a driving force for the Japanese contribution to international infrastructure in broadband seismology, notably on the ocean floor with programs such as the Ocean Hemispheres Project.

Even though he had to retire from teaching already in 2004, Yoshio Fukao remains impressively active in research, trying out new directions, as evidenced by his latest papers on ocean bores and fine-scale structure in the ocean column.

—Barbara A. Romanowicz, University of California, Berkeley; also at Collège de France, Paris


It is my great honor to be awarded the 2018 AGU Inge Lehmann Medal in recognition of my seismological contributions to solid Earth geophysics. I am especially grateful to Barbara Romanowicz for her citation and would like to thank all who supported my nomination.

My research career started with an experimental study of thermal properties of mantle minerals at the University of Tokyo about 50 years ago. This was to become the backbone of my seismological studies later on. I thank my colleagues in mineral physics, from whom I learned a lot about the rock physics view of Earth. I am deeply indebted to my thesis advisers, Seiya Uyeda and Hiroo Kanamori, for their continued thoughtful advice and encouragement. I spent a year in the 1970s as a postdoc at the University of Cambridge, where I learned a lot from Dan McKenzie about the plate tectonic view of Earth. I then spent 20 years at the early stage of my career at Nagoya University, where I enjoyed everyday discussions and conversations through which we shared surprise and excitement among the colleagues and students in different fields.

I, as a seismologist, have been interested in subduction dynamics and interaction of the solid Earth with the atmosphere and oceans. My findings in the first category include near-trench occurrence of tsunami earthquakes, subduction of untransformed oceanic crust, and, most importantly, stagnant slabs in the mantle transition region. Findings in the second category include Earth’s background free oscillations (Earth’s hum). Most of these findings were made in collaboration with my colleagues. In particular, I am grateful to Masayuki Obayashi, Kiwamu Nishida, and Hiroko Sugioka for their long-continuing collaborations in seismic tomography, Earth hum analysis, and ocean bottom seismology, respectively.

About 20–30 years ago I was involved in building a broadband seismographic network in the western Pacific in a Japanese initiative as part of the international collaborative effort of covering Earth’s surface with broadband seismic stations. I now belong to the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), where I am excited about deploying geophysical instruments at the ocean bottom in the hope to expand the scope of seismology beyond the solid Earth.

As such, I would have been unable to conduct my research without generous support from many people. I express my sincere gratitude to all of them, including my family.

—Yoshio Fukao, Japan Agency for Marine-Earth Science and Technology, Yokohama

Brian Kennett was awarded the 2017 Inge Lehmann Medal at the AGU Fall Meeting Honors Ceremony, held on 13 December 2017 in New Orleans, La. The medal is for “outstanding contributions to the understanding of the structure, composition, and dynamics of the Earth’s mantle and core.”



Brian Kennett’s innovations in theoretical seismology, as well as his profound and ­wide-­ranging observational studies, have had a lasting impact in geodynamics and geochemistry and have significantly improved the practice at international data centers for seismology.

In Cambridge, where he obtained his Ph.D. in 1973, he developed the first method to compute complete seismograms in layered models with control of reverberations. He combined this with observational studies of seismic waves at intermediate and high frequencies—work that eventually led to the ­two-­volume book The Seismic Wavefield. This is already a classic, broad in scope, encompassing ­near-­field strong ground motions to wave propagation on a global scale. After moving to Australia, he pioneered, with Rob van der Hilst, the first ­continent-­wide mobile array of broadband seismographs (­SKIPPY).

Brian took the lead in constructing a reference Earth model that gave accurate predictions of the travel times of the seismic phases for earthquake source location. With Bob Engdahl he developed the iasp91 model and further improved this by the addition of new travel time data on core phases (ak135). These models are now used by most international organizations as standards for the routine determination of earthquake locations and by a number of research groups performing ­high-­resolution seismic tomography using the travel times of seismic phases.

Of great importance has been his development of joint seismic tomography using the arrival times of both P and S waves to extract robust constraints on the distribution of bulk and shear moduli at depth. This work sparked an extremely productive effort among seismologists, mineral physicists, and geodynamicists to shed insight into the material nature of mantle heterogeneity. A lasting outcome from this endeavor is quantitative interpretations of ­3-D Earth structure in terms of thermal and compositional variations of the mantle in their relevant phase assemblages that link seismic and geodynamic interpretations of Earth structure in a consistent way.

In addition to his scientific work, Brian has been a mentor of numerous seismologists and a leader of the international seismological community, as president of the International Association of Seismology and Physics of the Earth’s Interior; editor of Geophysical Journal International for 20 years, Physics of the Earth and Planetary Interiors, and Earth and Planetary Science Letters; and nationally as director of the Research School of Earth Sciences in Canberra.

—Guust Nolet, Université de la Cote d’Azur, Nice, France; also at Princeton University, Princeton, N.J.


It is a singular honor to be awarded the AGU Inge Lehmann Medal for the facets of my work connected with the deeper Earth. I thank my nominator, Guust Nolet, and my supporters for their efforts on my behalf.

My research has been primarily based in seismology, with both observational and theoretical components directed at the understanding of seismic wave trains. These studies have also involved occasional collaborative forays into mineral physics and geodynamics. I have tended to work on seismological results at higher frequencies with particular emphasis on fine structure within the Earth that is likely to have the closest relationships to geochemistry and petrology.

Most of this work has been undertaken at the Australian National University, where Ted Ringwood encouraged my early work on the mantle, though he did not always like the answers obtained. Thanks to the push by Anton Hales for improved seismic travel times, I collaborated with Bob Engdahl and Ray Buland on the development of models that are now used for routine location by major international agencies. With the availability of travel times that are consistent between P, S, and the depth phases, it is possible not only to get better locations, notably in depth, but also to generate improved phase readings that can underpin ­high-­resolution tomographic imaging. Following reprocessing, the arrivals of both P and S waves can be exploited in joint tomography that allows the characterization of different heterogeneity regimes, as well as the delineation of major structures. With multiple images a more direct answer can be sought for the relative influences of temperature and composition.

New results frequently require a new approach. With Rob van der Hilst we established the first ­continent-­wide mobile array in the ­SKIPPY experiment across Australia. Among many other results, intriguing evidence of ­high-­frequency scattering in the inner core was brought to light in work with George Poupinet, thanks to a fortunate distribution of seismic events around Australia. Improved knowledge of shallow structure, utilizing adaptive stacking procedures and novel array designs, has also contributed to greater transparency for the influence of deep structure.

None of these efforts would have been possible without the unwavering support of my wife, Heather, my companion on a more than ­40-year journey exploring the Earth in depth.

—Brian Kennett, Australian National University, Canberra

Shun-ichiro Karato was awarded the 2016 Inge Lehmann Medal at the AGU Fall Meeting Honors Ceremony, held on 14 December 2016 in San Francisco, Calif. The medal is for “outstanding contributions to the understanding of the structure, composition, and dynamics of the Earth’s mantle and core.”



Prof. Shun-ichiro Karato is a thoroughly deserving recipient of AGU’s 2016 Inge Lehmann Medal for his seminal research in mineral and rock physics and its implications for our understanding of the structure and dynamical processes of the Earth’s mantle and core. Shun has built a formidable reputation as one of the foremost -mineral/-rock physicists of his generation by always choosing interesting and rewarding research problems and tackling them with a mix of creative experiments and original analysis and interpretation.

It is a characteristic of his work that experimental results are always placed in a wider context. This involves the use of appropriate models for material behavior, often drawn from the field of materials science, and a typically bold and provocative discussion of the application of the new insights to the behavior of the Earth. He has made multiple important contributions to our understanding of the deformation of Earth materials by developing and applying new experimental approaches for the study of the rheology of the —high—-pressure minerals of the transition zone and lower mantle, culminating in an —opposed—-anvil “rotational Drickamer” apparatus capable of –high–strain deformation in torsion at pressures reaching those of the uppermost lower mantle. This technique has recently allowed the first –large–strain deformation experiments on the wadsleyite and ringwoodite phases of the transition zone and the bridgmanite + ferropericlase mixture of the lower mantle, within their —high—-pressure stability fields, providing new insights into dislocation slip systems and rheology.

Shun has had a sustained interest in the influence of grain size, water, and partial melting upon rheology ever since his pioneering work in the 1980s delineating the boundary between the dislocation and diffusional creep regimes in –fine–grained olivine aggregates. The capacity of phase transformations occurring under conditions far from thermodynamic equilibrium to drastically reduce grain size and thus influence the rheology of the cool interiors of subducting slabs has also been emphasized. He first suggested that partial melting of the mantle might strengthen it by removing water from minerals into the melt. He has also actively explored the link between deformation and the development of fabric with important implications for seismic anisotropy in the upper mantle and in the inner core, where he has suggested a role for the magnetic field. Shun has been an influential thinker about seismic wave attenuation and dispersion. In recent years, he has led studies of the effect of water in nominally anhydrous minerals on their electrical conductivity, rheology, and deformation fabrics.

The breadth and depth of Prof. Karato’s contribution to our understanding of the mechanical behavior of geological materials are well illustrated by his powerful synthesis Deformation of Earth Materials, published by Cambridge University Press.

—Eiji Ohtani, Tohoku University, Sendai, Japan; and Ian Jackson, Australian National University, Canberra, ACT, Australia


Thank you Eiji and Ian for your kind nomination of me for the Lehmann Medal. Thank you also to those who supported this nomination and the committee members. It is my great pleasure to receive this honor for what I have done during the last ~40 years of my life.

I was born in Fukuoka, Japan, 4 years after the end of the Second World War and became a student of the University of Tokyo in 1968. That was a special year. In 1968, the model of plate tectonics was established, and the student rebellion spread throughout the world and there was no lecture at the University of Tokyo for more than a year. But this was the year in which I learned the most. I became an independent student and finished my Ph.D. without a supervisor. When I was struggling to become a scientist, luckily enough I had a chance to spend a few years at Australian National University (ANU) in Canberra. The time in Canberra was just so wonderful both scientifically and personally. In a very relaxed atmosphere, people there conducted –world–class scientific studies. For the first time in my life, I got rigorous training as an experimentalist. I also learned that there are different styles of conducting scientific studies. Developing “bold” hypotheses and testing them with rigorous approaches is one way of doing science that I learned at ANU.

When I was a student, I got fascinated by geodynamics but soon realized that understanding materials properties is a key to putting a strong physical basis on geodynamics. Among various physical properties connected to geodynamics, I chose rheological properties and the role of water on various properties as the topics of my studies. These are the problems in “mineral physics,” but I have been trying to go beyond conventional mineral physics. I focused on issues that are closely connected to geophysical observations.

In studying these problems new approaches are sometimes needed, including technical developments. Developing a new technique is essential but challenging in the busy recent scientific community. I was fortunate to enjoy much support from colleagues including students and postdocs that made this challenge sometimes successful. In particular, I should mention colleagues in Tokyo, Canberra, Minnesota, and New Haven. And, last but not least, I thank my family (my wife Yoko and each of our parents). Without their selfless support I would not be here today. Thank you all.

—–Shun-ichiro Karato, Yale University, New Haven, Conn.

Peter Olson was awarded the 2015 Inge Lehmann Medal at the AGU Fall Meeting Honors Ceremony, held on 16 December 2015 in San Francisco, Calif. The medal is for “outstanding contributions to the understanding of the structure, composition, and dynamics of the Earth’s mantle and core.”



Throughout his career Peter has inspired students and fellow geophysicists with his scientific insight and explanations and has gained international respect as a leader in studies that have improved our understanding of the structure and dynamics of the Earth’s interior. Peter has made significant scientific advances related to both the mantle and core of the Earth, two very different regimes requiring very different research expertise. Peter has accomplished this via two different approaches: numerical modeling and laboratory experiments.

Peter developed some of the original models of tectonic plate motions coupled to convectively driven mantle flows and of heterogeneous chemical composition of the mantle due to subducting slabs and rising plumes. He supported these theories and model simulations with the first laboratory experiments using variable-viscosity corn syrups, which provided explanations for surface observations like “trench rollback” and seismic observations like subducting slab deformation and partial penetration into the lower mantle. Peter is a coauthor of the comprehensive book Mantle Convection in the Earth and Planets (2001), which reviews the huge advances made over many decades in our understanding of mantle dynamics.

Peter has also studied the Earth’s core using numerical simulation and laboratory experiments. He motivated and led the first parametric study of hundreds of planetary dynamo simulations to learn how the structure, intensity, and time dependence of the resulting magnetic fields depend on various parameters of the model. His work led to the identification of different regions in parameter space that determine the frequency of dipole reversals based on convective versus rotational effects. In one region dominated by rotation Peter showed that magnetic dipole reversals do not occur; in another dominated by convection dynamos continuously reverse, and between these two regions the dynamo only occasionally produces dipole reversals. The geodynamo falls into this third parameter regime. Using laboratory experiments, Peter demonstrated how a rapidly rotating and strongly convecting sphere of fluid produces columnar flow patterns, which are critical for the geodynamo. He also conducted experimental studies of magnetoconvection and the growth of the Earth’s inner core. By organizing and editing Core Dynamics, volume 8 in the Treatise on Geophysics (2007), Peter provided a valuable resource that describes our current understanding of the Earth’s core.

—Gary A. Glatzmaier, University of California, Santa Cruz


Thank you, Gary, for the generous citation and for working with other colleagues to advance my nomination for the Lehmann Medal. I am very aware that recognition like this stems from the efforts of many folks, and it is humbling and deeply satisfying to be selected as a contributor to our understanding of the deep Earth.

I first became an American Geophysical Union member in 1978, and it is remarkable to recall the limited state of understanding of the vast region of the lower mantle at that time. Seismic velocity models and associated geodynamical and mineralogical interpretations were not dramatically different from those available in the days of Inge Lehmann’s seminal work on the inner core. The accumulation of analogue recordings by the worldwide standardized seismological network and advances in numerical methods for computing seismic waves for one-dimensional Earth models had set the stage for moving forward, but few seismologists were working on deep-mantle problems. Indeed, my own work with Don Helmberger was initially focused on quantifying upper mantle lateral variations, and when we first advanced interpretations of deep-mantle discontinuity structure, the general response by the few who cared was rather dismissive skepticism.

Fast-forwarding to today, progress has been dazzling, with a large and vigorous international interdisciplinary research community advancing the frontiers of our knowledge. This is reflected in a proliferation of unpronounceable acronyms like LLSVP (large low-shear velocity provinces), ULVZ (ultralow velocity zones), and pPv (postperovskite) and the integrated efforts by organizations like SEDI (Study of the Earth’s Deep Interior) to understand the detailed chemistry, transport properties, and evolution of the deep mantle and core. Topics such as deep-mantle anisotropy, barely suggested in work preceding 1978, now engage joint seismological, geodynamical, and mineralogical modeling efforts that build upon state-of-the-art capabilities of different disciplinary efforts.

Our understanding of the deep mantle and core is now sophisticated, but great uncertainties and challenges remain; I am sure that the next generation of results will revise some of our current paradigms, and hopefully, it will provide new acronyms that are easier to say.

I’ve been very fortunate to work on seismology of the deep mantle and core with wonderful mentors, colleagues, and graduate students, along with receiving institutional support from great programs at the California Institute of Technology (Caltech), the University of Michigan, and the University of California, Santa Cruz. This recognition is shared among us all, and I deeply appreciate the many collaborations.

—Peter Olson, Johns Hopkins University, Baltimore, Md.

Thorne Lay was awarded the 2014 Inge Lehmann Medal at the AGU Fall Meeting Honors Ceremony, held on 17 December 2014 in San Francisco, Calif. The medal is for “outstanding contributions to the understanding of the structure, composition, and dynamics of the Earth’s mantle and core.”



Thorne Lay has made contributions to our knowledge and understanding of deep Earth structure that have had an exceptional multidisciplinary impact, as have his contributions to the study of earthquakes.

As a graduate student with Don Helmberger in the early 1980s, his discovery of the discontinuity at the top of the D˝ region in the lowermost mantle, now sometimes called the “Lay” discontinuity, attracted the attention of the community to a region of the mantle that previously had been somewhat neglected. At the time, this was quite an achievement, using for the most part analog, noisy data from a not-so-large global seismic network. These observations have since been confirmed by many independent studies. Perhaps most importantly, they have inspired the mineral physics community, culminating in the discovery, 10 years ago, of the postperovskite (pPv) transition in magnesium at pressures and temperatures corresponding to those in the vicinity of Earth’s core-mantle boundary.

Since then, Thorne has been at the forefront of intellectual efforts to characterize the consequences of these findings for the interpretation of complexities in the seismic structure at the base of the mantle, such as the possible double occurrence of the pPv, folded slabs, and partial melting at the base of the mantle.

Even before the pPv transition “explosion,” Thorne and his students, postdocs, and collaborators continued over the years to document lateral variations in the D˝ discontinuity as well as other complexities, such as seismic anisotropy and velocity gradients. He largely contributed to the development of the broad picture that we now have of the fine-scale structure of the D˝ region.

So far, I’ve only described one aspect of Thorne’s research, the one most relevant to the “theme” of the Inge Lehmann Medal. I also wish to mention his important contributions to the question of howmegaearthquake ruptures develop on the rupture plane. Starting as a graduate student with the development of the “asperity” model with Hiroo Kanamori, he has picked up this question very actively in recent years, taking advantage of the newly available high-quality seismic broadband array data, which have coincided with the occurrence of several megaearthquakes in the last decade, and he has often been among the first to document their unusual rupture behaviors.

Finally, it is important to stress Thorne Lay’s community leadership, as manifested by his role in the Incorporated Research Institutions for Seismology and his endless dedication as a spokesman for the solid Earth community, where we often rely on his clear and articulate thinking.

—Barbara Romanowicz, University of California, Berkeley, and Collège de France, Paris, France


Thank you, Barbara, for the generous citation and for working with other colleagues to advance my nomination for the Lehmann Medal. I am very aware that recognition like this stems from the efforts of many folks, and it is humbling and deeply satisfying to be selected as a contributor to our understanding of the deep Earth.

I first became an AGU member in 1978, and it is remarkable to recall the limited state of understanding of the vast region of the lower mantle at that time. Seismic velocity models and associated geodynamical and mineralogical interpretations were not dramatically different from those available in the days of Inge Lehmann’s seminal work on the inner core. The accumulation of analog recordings by the worldwide standardized seismological network and advances in numerical methods for computing seismic waves for one-dimensional Earth models had set the stage for moving forward, but few seismologists were working on deep-mantle problems. Indeed, my own work with Don Helmberger was initially focused on quantifying upper mantle lateral variations, and when we first advanced interpretations of deep-mantle discontinuity structure, the general response by the few who cared was rather dismissive skepticism.

Fast-forwarding to today, progress has been dazzling, with a large and vigorous international interdisciplinary research community advancing the frontiers of our knowledge. This is reflected in a proliferation of unpronounceable acronyms like LLSVP (large low-shear velocity provinces), ULVZ (ultralow velocity zones), and pPv (postperovskite) and the integrated efforts by organizations like SEDI (Study of the Earth’s Deep Interior) to understand the detailed chemistry, transport properties, and evolution of the deep mantle and core. Topics such as deep-mantle anisotropy, barely suggested in work preceding 1978, now engage joint seismological, geodynamical, and mineralogical modeling efforts that build upon state-of-the-art capabilities of different disciplinary efforts.

Our understanding of the deep mantle and core is now sophisticated, but great uncertainties and challenges remain; I am sure that the next generation of results will revise some of our current paradigms, and hopefully, it will provide new acronyms that are easier to say.

I’ve been very fortunate to work on seismology of the deep mantle and core with wonderful mentors, colleagues, and graduate students, along with receiving institutional support from great programs at the California Institute of Technology (Caltech), the University of Michigan, and the University of California, Santa Cruz. This recognition is shared among us all, and I deeply appreciate the many collaborations.

—Thorne Lay, University of California, Santa Cruz, Calif.

Bradford H. Hager was awarded the 2013 Inge Lehmann Medal at the AGU Fall Meeting Honors Ceremony, held on 11 December 2012 in San Francisco, Calif. The medal is for “outstanding contributions to the understanding of the structure, composition, and dynamics of the Earth’s mantle and core.”



In the post–plate tectonics world, efforts to map the structure of Earth’s interior broadened to include a growing preoccupation with the underlying dynamics. Students of global geophysics recognize the important role that previous recipients of the Inge Lehmann Medal played in this effort, but they would also understand the reasons that Bradford Hager of the Massachusetts Institute of Technology must be included in this honored list. Brad has been a central figure in mantle dynamics for the last 30 years, responsible for many fundamental advances in our understanding of mantle structure and flow and their connection to the geological record.

Beginning in the early 1980s, Brad’s development of kinematic and dynamic models of global mantle flow provided a new framework for numerical simulations of mantle convection that remains at the heart of modern global geophysics. His inspired research moved the field away from the two-dimensional Cartesian models that emerged following plate tectonics toward global models that could be related to seismic and rheological structure and directly compared to global data sets. The list of Brad’s contributions during this period remains a critical part of what many believe was a golden age of research in mantle dynamics.

As a graduate student at Harvard working with Rick O’Connell, he demonstrated that seismicity along subducted slabs was inconsistent with the prevailing view of layered mantle flow, and his argument for whole-mantle convection remains a foundation of global geophysics. Later, at the California Institute of Technology, he and Mark Richards elucidated the connection between mantle convection and Earth’s geoid, in particular the physics associated with dynamic topography and mantle viscosity. Their inference that mantle viscosity increased significantly from the upper to lower mantle boldly challenged conventional thought, and it has prevailed.

Brad’s contributions to mantle dynamics have continued unabated. His model for mantle compositional stratification, developed with Louise Kellogg and Rob van der Hilst, catalyzed debate on the nature of mantle thermochemical structure. Furthermore, his argument with Gene Humphreys that a Rayleigh-Taylor instability in the lithosphere was responsible for the origin of the Transverse Ranges in Southern California is a seminal example of research at the interface between mantle flow and the geological record. Moreover, working with Clint Conrad, Brad demonstrated that plate-bending stresses at subduction zones play a critical role in plate dynamics and the overall driving force for plate tectonics. This last example leads me to add another important contribution, namely, that Brad’s students and postdocs, including Mark Richards, Scott King, Mike Gurnis, Mark Simons, Clint Conrad, Lindy Elkins-Tanton, and Brendan Meade, have moved on to notable careers in the advancement of our discipline.

Most citations are to some extent personal, and this one is no exception. I will always remember Brad’s generosity over 20 years ago, at a meeting in Erice, when he sat with a graduate student for two hours and discussed a research problem with patience and deep physical insight. Thanking him for this act of graciousness toward a young student and honoring him with this major award from our entire community are both overdue.

—JERRY X. MITROVICA, Harvard University, Cambridge, Mass.


Thank you, Jerry, for your very kind words. I am delighted, surprised, and honored. I have been very lucky to be in the right places at the right times and with the right people all my career. I can’t think of another person blessed with as many exceptionally talented and passionate students and postdocs as well as fantastic faculty colleagues. I wish that I had the space to do each of you justice here. Thank you all.

I entered graduate school at Harvard during a singular time. My fellow students, including Ed Stolper, Tim Grove, Andy Knoll, and Hap MacSween, both challenged and taught me. Among other gifts, they gave me a practice general exam that made the real exam seem easy. In addition to handing me an outstanding thesis topic, Rick O’Connell ran a seminal seminar on mantle dynamics in which faculty, postdocs, and grad students contributed as equals. Four future Lehmann Medalists were there, including Rick, John Woodhouse, and Barbara Romanowicz, so I got a chance to romp with the big dogs. Adam Dziewonski made me feel like an apprentice big dog myself, including me as second author on his first paper presenting a global tomographic model, fixating me on the challenges of reconciling seismology, geodesy, and geodynamics.

Summer schools provided more chances to engage; Adam, Enzo Boschi, Keith Runcorn, and Nafi Toksöz provided pivotal opportunities during my formative years. I hardly deserve mention for spending a couple of hours with you in Erice, Jerry—I got more out of picking the brains of an up-and-coming star than you got from me.

At Stony Brook I absorbed the importance of mineral physics from Bob Liebermann and Don Weidner, as my good fortune learning from future Lehmann medalists continued.

At Caltech’s Seismo Lab, I felt like a kid in a candy store! Coffee hour discussions with Don Anderson, Hiroo Kanamori, Don Helmberger, and a brilliant cohort of students were exquisitely stimulating. Working with Rob Clayton and Gene Humphreys, as well as with Adam during his sabbatical, on the geodynamical implications of their astonishing tomographic models provided a downright mystical experience. Their tomographic models set the stage for Mark Richards and me to develop a dynamically consistent explanation of Earth’s geoid in terms of mantle flow.

Another stroke of good fortune was the advent of GPS—at last I could do physics outside! Tom Jordan provided me a new candy store—MIT—where Tom Herring, Peter Molnar, and others were initiating GPS studies of regional tectonics. I frolicked with them and others, measuring mountains being built and earthquake strain accumulating and releasing.

Finally, I note how special it is to receive AGU’s medal honoring Inge Lehmann, not only because her discoveries ranged from the inner core to the uppermost mantle but also because she excelled at a time when women scientists were rare. I have been associated with bright, courageous women all of my life. My brilliant mother was forbidden by her father to go to college because she was female. I wish that she could have seen me get an award named for a woman pioneer! She did see my wife, Patty, and our daughters, Emily and Anna, experience the joy of academic pursuits, knowing that they are free to run fast and far with their talents. I end by thanking all these women for inspiring me beyond geodynamics.

—BRADFORD H. HAGER, Massachusetts Institute of Technology, Cambridge

Donald J. Weidner was awarded the 2011 Inge Lehmann Medal at the AGU Fall Meeting Honors Ceremony, held on 7 December 2011 in San Francisco, Calif. The medal is for “outstanding contributions to the understanding of the structure, composition, and dynamics of the Earth’s mantle and core.”



We honor Donald Weidner for his pioneering experiments on the elastic and rheological properties of Earth materials in conjunction with synchrotron X-radiation and for his outstanding leadership in high-pressure mineral physics. For his early work applying Brillouin spectroscopy to measuring the elastic properties of single crystals, Don received AGU’s Macelwane Medal 30 years ago.

With the establishment of the High Pressure Laboratory at Stony Brook University in 1985, Don led the installation of a multianvil, high-pressure apparatus on the superconducting wiggler beamline at the National Synchrotron Light Source of the Brookhaven National Laboratory. Using this apparatus, Weidner and his colleagues have performed pressure-­volume-­temperature measurements of the equations of state for many mantle minerals and developed techniques to use the X-ray diffraction spectra to elucidate the state of deviatoric stress acting on the specimens under high pressures and temperatures. In collaboration with Yanbin Wang, William Durham, and Ivan Getting, Don developed a new type of high-pressure deformation apparatus capable of generating pressures of up to 15 gigapascals and temperatures of up to 2000 K in conjunction with synchrotron X-radiation.

Weidner’s experimental work has always been focused on improving our understanding of the chemical evolution, global structure, and dynamics of the Earth’s mantle. Such an approach is all too infrequent in petrology and mineral physics but is critical in making these experimental results useful to the global geophysical community. These interpretative papers have also been used by Weidner to guide the future thrusts of his experimental laboratory program.

Weidner was the founder and is the director of the Mineral Physics Institute (MPI) at Stony Brook University. MPI served as the headquarters from 1991 to 2002 of the National Science Foundation (NSF) Science and Technology Center for High Pressure Research (CHiPR), for which Weidner served as director and principal investigator, in collaboration with Alexandra Navrotsky, Charles Prewitt, and Robert Liebermann.

The other aspect of Weidner’s career worthy of recognition is his enormous service to the broad mineral physics community. In 2002 he was the principal architect of a new NSF-funded initiative, the Consortium for Materials Properties Research in Earth Sciences (­COMPRES), and served as the founding chair of the Executive Committee. COMPRES is now a flourishing enterprise with 56 U.S. member institutions and 39 foreign affiliates and provides funding for the operation of community facilities at national laboratories and infrastructure development of new technologies for high-pressure experimentation.

For his significant and distinctive contributions to technological advances in mineral physics, his determination of the physical properties of many mantle minerals and their high-pressure phases, his papers using mineral physics data to determine the chemical composition and mineralogy of the Earth’s mantle, and his leadership of COMPRES, we are pleased to honor Don Weidner with the 2011 AGU Inge Lehmann Medal.

—Robert Liebermann, Department of Geo­sci­ences and Mineral Physics Institute, State University of New York at Stony Brook; and Guy Masters, Scripps Institution of Oceanography, University of California, San Diego, La Jolla


Bob, thank you for your kind words. AGU, thank you for this honor. I particularly appreciate the recognition of the important role that mineral physics plays in understanding the Earth’s interior.

After being raised in the farmland of Ohio, in search of college training I traveled to the mecca of education, Cambridge, Mass. Four years at Harvard and 5 years at the Massachusetts Institute of Technology (MIT) changed my view of the world. The extremes of the excitement and the work of learning opened my eyes to a wholly new view of life. Finally, in graduate school, I had sharpened my student skills to the point that I realized I had a choice: I could either get an A in a course or learn something. But I couldn’t do both. I quickly finished my course work and stepped into the world of research. Once again, my world view made a big change. Scholarship transitioned from a world of drudgery to one of enormous excitement. I’m still in that place today. I have always marveled at the fact that I get paid to do the things that I really enjoy doing.

My Ph.D. thesis was with Kei Aki, studying Rayleigh waves from mid-Atlantic earthquakes. Kei was a great role model: brilliant, insightful, and always a bit surprised that I had missed some obscure study that might have a vague application to my work. It was during this time that my fascination of the deep Earth was baked into my soul. Nafi Toksoz told me of a faculty position at Stony Brook and suggested that I apply. I thus transitioned to Stony Brook directly from graduate school to assistant professor.

Inspired by Prewitt and Papike, who were studying tiny crystals with X-rays, I found a tool to study elastic properties of these small minerals. Brillouin spectroscopy played to my physics undergraduate degree and yet allowed me to focus on the properties of the mantle. I needed samples, and the Japanese had taken the lead in creating high-pressure phases with large volumes. This led to my lifelong friendship with many Japanese colleagues: Akimoto, Yagi, Ito, Kumazawa, Shimomura, Fukanaga, and many more.

Liebermann, Prewitt, and I bought some equipment from the Japanese companies and were ready to push high-pressure studies on a couple of fronts, at which point Prewitt decided to accept the directorship of the geophysical lab and left us. Bob Liebermann and I decided that Bob would take the lead on the in-house system and I would oversee the synchrotron system. At that point I could barely spell synchrotron, and I knew little about X-ray tools. But this has become one of the most fascinating adventures in my career. One can literally see the sample at high pressure and temperature, and Li Li showed us how to make quantitative measurements on it. New observations continue to open up that give insights into the behavior of the material and how that behavior affects the deep Earth.

Success in this journey has been supported by colleagues who are irreplaceable. We simply would not have succeeded without them. Mike Vaughan has been a vital part of the synchrotron effort and a great friend. I have been surrounded by stimulating, brilliant, and capable people such as Li Li and Bill Huebsch. Many people at the National Science Foundation have made a great difference to our field. Robin Reichlin and Sonia Esperanca care about the science and the people.

I must acknowledge my parents, who gave me both the tools and the permission to achieve, and my older brother, Jerry, who was always a great role model and my strongest supporter.

I choose to celebrate with my colleagues and friends, as this award recognizes the contribution of us all.

Thank you.

—Donald J. Weidner, Department of Geosciences and Mineral Physics Institute, State University of New York at Stony Brook

Barbara A. Romanowicz was awarded the 2009 Inge Lehmann Medal at the AGU Fall Meeting Honors Ceremony, held on 16 December 2009 in San Francisco, Calif. The medal is for “out-standing contributions to the understanding of the structure, composition, and dynamics of the Earth’s mantle and core.”



It is my pleasure to introduce Barbara Romanowicz as the seventh recipient of the AGU Inge Lehmann Medal. Barbara’s work covers the full span of seismological studies from the crust to the inner core—not unlike Inge Lehmann’s. Barbara’s transformational contributions come from her investigations of attenuation (Q) in the Earth and, in particular, its lateral variations. This is an enormously difficult research area, since studies of attenuation require measurements of amplitude, and amplitudes, unlike the phase, depend on the details of the laterally varying structure. Barbara’s studies of lateral variations in attenuation began 20 years ago. In 1994, she discovered the pattern of attenuation in the transition zone and its correlation of low-Q with the distribution of hot spots. More recently, she developed a new three-dimensional (3-D) model of Q and pointed out the correlation of occurrence of superplumes in the lower mantle and attenuation in the transition zone.

The other area of Barbara’s fundamental contributions concerns application of asymptotic properties of normal modes to studies of lateral heterogeneity. Following early theoretical developments, she molded it into a tool used to obtain 3-D seismic velocity models. Her models of lateral heterogeneity have improved in the radial and horizontal resolution and are among those most frequently cited. Her work has now expanded to inversion for anisotropy, on both global and regional scales. She published a series of studies on the structure of the inner core, particularly its anisotropy. Most recently, she observed a change in the PKiKP amplitude over a period of 10 years, attributed to short-wavelength topography on the inner core boundary; differential rotation is one possible explanation.

The “Earth’s hum” is a beautiful example of coupling between the atmosphere, oceans, and solid Earth. Winds cause ocean waves that in turn excite free oscillations of the Earth observed in a range of periods from 200 to 500 seconds. Barbara was the first to locate the regions of the oceans where most of the excitation occurs: the North Pacific in winter and Southern Ocean in summer.

While Barbara’s research accomplishments are remarkable and should be sufficient for awarding her a medal, a description of her career would be incomplete without mentioning her contributions to the seismological infrastructure. A very major early effort was the establishment of a global network called Geoscope; with the first stations installed in 1982–1983, this effort preceded the Global Seismographic Network initiative of the Incorporated Research Institutions for Seismology (IRIS). Geoscope fills in vital locations in global coverage and produces excellent data, available to all. Not the least is her role in bringing back to eminence the seismographic network, and seismology in general, at University of California, Berkeley. As the director of the Seismological Laboratory for nearly 20 years, she has developed a number of new programs not only in broadband seismology but also in geodesy. She is leading the effort to establish the Cooperative Institute for Dynamic Earth Research (CIDER), intended to build a new, interdisciplinary approach to solving complex problems in Earth sciences.

In my opinion, Barbara is the most outstanding woman seismologist after Inge Lehmann. I believe it is most appropriate for AGU to award her the medal named after her predecessor.

—ADAM M. DZIEWONSKI, Harvard University, Cambridge, Mass.


Thank you, Adam, for your generous and flattering introduction. Thanks to AGU for deeming me worthy of this honor, and to my graduate students, postdocs, and collaborators, who share this award with me today.

Studies of the Earth’s mantle and core span several sections of AGU. I feel fortunate to be awarded the Inge Lehmann Medal this year, as I know there is a long waiting list of highly deserving colleagues.

Many roads lead to Rome, and a variety of paths lead to becoming a seismologist. In my case, as in many others’, it happened quite by chance. Not unlike Inge Lehmann, my training was in mathematics. After finishing my bachelor’s degree, I happened upon a poster advertising a master’s program in fundamental astronomy, including 2 weeks of training at the Observatoire du Pic du Midi, in the high Pyrenees. At that time, I would have jumped on any opportunity to leave the city and climb mountains.

This led me to the calculation of orbits of spacecraft around the Earth and the Moon that are affected by perturbations in the gravitational field. This was not long after the discovery of lunar “mascons” and when the first high-order descriptions of the Earth’s geopotential from satellite measurements were being produced. For me, it was the first encounter with the study of the Earth’s interior. This ultimately led me to the Institut de Physique du Globe de Paris (IPG) to work toward a Ph.D. with Kurt Lambeck, on the inversion of gravity data. One day I wandered onto the seismology floor at IPG and found Georges Poupinet displaying colorful global maps of seismic travel time anomalies—these were precursors of seismic tomography—and I soon discovered that seismology provides far better constraints on deep-Earth structure than gravity. Thirty years later, I still enjoy seismology as my primary research tool.

I am grateful to Kurt Lambeck for getting me off to a good start, and to Claude Allègre for making IPG a stimulating research environment and for entrusting me with the Geoscope program. I had the privilege of having Kei Aki as a postdoc advisor and Adam Dziewonski as a partner in several rewarding initiatives over the years, starting with the International Federation of Digital Seismograph Networks, the International Ocean Network, and more recently, CIDER. The University of California, Berkeley has been a wonderful place to work for the past 18 years.

I thank my parents for broadening my horizons by bringing me up bilingual and for having the foresight to send me to England at the age of 10, anticipating that a fluent knowledge of English would facilitate whatever career I chose in today’s world.

Last but not least, I wish to thank my husband, Mark Jonikas, for his infinite patience and support, and my children, Martin and Magda, for their cooperation by having slept through the night from the age of 2 months, by having spared us any teenage crises, and by having turned into fine young adults, both now starting their own post-Ph.D. careers in science.

—BARBARA A. ROMANOWICZ, Berkeley Seismological Laboratory, University of California, Berkeley

Ho-kwang Mao was awarded the 2007 Inge Lehmann Medal at the AGU Fall Meeting Honors Ceremony, which was held on 12 December 2007 in San Francisco, Calif. The medal is for “out-standing contributions to the understanding of the structure, composition, and dynamics of the Earth’s mantle and core.”



The Inge Lehmann Medal is awarded in recognition of “outstanding contributions to the understanding of the structure, composition, and dynamics of the Earth’s mantle and core.” When Ho-kwang (Dave) Mao completed his Ph.D. in 1968 at the University of Rochester and moved to the Geophysical Laboratory, a revolution in how we could achieve that understanding was in the making.

Over the following four decades, Dave Mao redefined solid Earth geophysics, demonstrating that the mantle and core are accessible in the laboratory through direct study of their components at high pressures and temperatures. Through diverse, ingenious experimentation, this journey to the center of the planet has revealed the many dramatic ways that Earth materials transform under extreme conditions and established a materials-based understanding of the deep interior.

Dave’s first paper in JGR, based on his M.S. thesis, broke new ground in studies of the core by demonstrating polymorphism in iron alloys. This theme has continued throughout his career, leading to diverse studies of the phase diagram, equation of state, and optical, elasticity, and texture measurements, all at pressures of the core. Work on oxides and silicates that commenced with his Ph.D. thesis addressed the complete range of upper and lower mantle minerals. Dave and his group established the full suite of properties of silicate perovskites, including phase relations with accessory oxides and volatile components. His papers 30 years ago proposed that magnesium-rich silicate perovskite is the most abundant mineral in the planet, a paradigm that remains intact to this day. Recent work is revealing the nature of silicate postperovskite and the core-mantle boundary region.

Dave accomplished this by focusing on the development of instrumentation that could, first, recreate the entire range of pressures and temperatures of the deep interior, and, second, allow accurate measurements under those conditions. His revolutionary refinements of the diamond anvil cell with Peter Bell established that static megabar pressures could be achieved in the laboratory, and steadily advanced the range of accessible pressures to the inner core. A remarkable array of techniques were developed and applied, from lasers to synchrotron radiation to neutron methods. These accomplishments in experimental geophysics have been a windfall for other disciplines, leading to numerous discoveries beyond geoscience.

During my first experiments with Dave, I realized his key to success: an uncanny ability to distill a scientific problem into an experiment, to develop an appropriate technique, and to go into the lab and solve it, all with infectious enthusiasm and a generous spirit. Nearly every leading group in the field of static high-pressure research worldwide has benefited from contact with Dave, or from the people he has trained.

This is Dave’s first medal from AGU, surprising given his numerous other accolades, including membership in not one but three National Academies, his many other medals, and the fact that Dave identifies himself as a geophysicist. Since that first article in JGR, Dave has published some 683 papers with 411 different coauthors; countless others he has influenced directly or indirectly, all testament to a body of work that has profoundly influenced our understanding of the mantle and core. Moreover, this productivity and impact show no sign of deceleration. I present Ho-kwang Mao, the Lehmann Medalist for 2007.

—RUSSELL J. HEMLEY, Geophysical Laboratory, Carnegie Institution of Washington, Washington, D.C.


Thank you, Rus, for those kind words, and thanks to the rest of my colleagues, postdocs, and students at the Geophysical Laboratory and around the world with whom I have had the good fortune and pleasure to collaborate.

It is an honor to receive this medal, named after the extraordinary scientist who discovered the Earth’s inner core. The behavior of iron in lower mantle silicates and the core has been a key and constant thread throughout my career. I would like to thank my Ph.D. advisors, Bill Bassett and Taro Takahashi, who discovered the hexagonal close-packed iron in 1964, and introduced me to the diamond anvil cell. As Rus mentioned, the topic of my masters thesis–and of my first article published exactly 40 years ago was–the equation of state of iron alloys. I then had the good fortune to work with Peter Bell, developing the megabar diamond anvil cell together, and my first megabar article published in JGR in 1979 was on iron. I would also like to thank Rus Hemley for pushing physics and chemistry onto this geophysicist, which greatly expanded my horizon or depth in reaching 3 megabar and high temperatures with X-ray diffraction, imaging, and spectroscopy for crystal chemistry, crystal structure, seismic velocities, and rheological properties, again on iron.

Although there have been significant advances in the field of mineral physics in improving in situ characterization methods and reaching ever more extreme conditions, we still have not reached both inner core pressure and temperatures simultaneously. In the meantime, seismologists have made remarkable progress in increasing our understanding of the Earths deep interior. It is fitting that the first Lehmann medalist was Don Helmberger, who opened so many inner core challenges for us to tackle. Therefore I am accepting this medal as a challenge to all mineral physicists. We have a lot to do to help explain the complex and rich behavior observed in the most remote regions within our planet.

It is particularly apt that Inge Lehmann was a woman, since my life has been profoundly influenced by women. Among the many I would like to thank is my mother, who spurred me to pursue a career in science and would not be satisfied with anything less than excellence. My three daughters, Cyndy, Linda, and Wendy, have been a source of equal parts joy, pride, and befuddlement. My youngest daughter, Wendy, has been foolish enough to pursue a career in experimental mineral physics. Proving that the apple falls not far from the tree, her Ph.D. topic was on the behavior of iron in the D” layer and core.

Last, but far from least, I thank my lovely and patient wife, Agnes. To all who know me, it is clear that she is the real force behind my research and everything in my life. As proof, she had the good sense to forbid me from wearing a 30-year-old tuxedo I had been deluded into believing might still be a good fit. Alas, like the inner core, my midsection has grown a lot over time.

—HO-KWANG MAO, Carnegie Institution of Washington, Washington, D.C.

Thomas H. Jordan was awarded the Inge Lehmann Medal at the 2005 AGU Fall Meeting Honors Ceremony, which was held on 7 December in San Francisco, Calif. The medal honors outstanding contributions to the understanding of the structure, composition, and dynamics of the Earth’s mantle and core.



Tom Jordan entered geophysics when the plate tectonic revolution was already in full swing. The basic tenets had been worked out, but there remained two basic questions: How do continents fit into this essentially oceanic theory, and what is the style of mantle convection that accompanies the motions of the plates?

Answers to these questions had already been proposed by others. In the case of continents, it was argued that continental crust was all that distinguished continental and oceanic lithosphere. The subcontinental mantle and oceanic mantle were thought to be the same, so that the thickness of either type of lithosphere could simply be explained by conductive cooling. This proposal was simple and elegant, requiring only a modest extension of plate tectonic theory to include the continents. There were also early proposals regarding the pattern of mantle convection that necessarily accompanied surface plate motion. The prevailing wisdom at the time was that plate-related convection was superficial, restricted to the Earth’s upper mantle.

It was in such an environment that Tom made fundamental advances toward our understanding of continents and of mantle convection. Based primarily on travel-time measurements of vertically propagating shear waves, combined with observations of gravity and the composition of mantle xenoliths from old continents, he argued that the mantles beneath old continental crust and old oceanic crust were not the same, with old continents being underlain by thick roots of intrinsically lighter material.

At first glance, this proposal appeared to complicate plate tectonics. How could plates move if the continents possessed such thick roots? But he was right. The tectosphere hypothesis that describes the structure and survival of compositionally distinct, basalt-depleted continental lithospheric mantle is now the cornerstone of continental thought and has been confirmed many times over. Earth science is still struggling with the problem of how such ancient continents formed and evolved, but any such hypothesis must account for the formation of continental tectosphere.

Regarding the issue of mantle convection, Tom devised a powerful observational test for convective style, namely, tracing the fate of subducted slabs by way of the expected signature of the cold slabs on seismic velocity. If slabs could be identified in the lower mantle, then this would argue for the participation of the lower mantle in mantle convection. Again a simple test, again a controversial, unconventional result, again a fight, and again a win. Tomographic images produced decades later have confirmed the penetration of slabs into the lower mantle, consistent with whole-mantle convection.

Tom Jordan has made other advances in geophysics that are too numerous to mention. But these two contributions serve to illustrate several of Tom’s qualities that make him a scientist of the first rank: He has a taste for fundamental problems, a profound respect for seismic observations, a facility for theory that permits a remarkably powerful analysis of data, and the love of the fight that enables him to confidently take on conventional wisdom. It is truly a winning combination.

On a personal note, I have interacted with Tom as his student during those wild, controversial years, as a colleague, and as a friend. It is my pleasure to introduce the 2005 winner of the Inge Lehmann Medal, Tom Jordan.

—PAUL G. SILVER, Carnegie Institution of Washington, D.C.


I traveled to my first San Francisco AGU meeting in 1968 while still an undergraduate at the California Institute of Technology, hitchhiking up the hippie highway to see what geophysics was all about. It seems like yesterday, but I realize it was 37 meetings ago. At that time, the Earth’s interior was still represented as a layered sphere, and we had almost no information about the strange structures within its opaque depths. Pioneers like Inge Lehmann who probed this terra incognito were my heroes, so it is a special honor to receive a medal that commemorates her remarkable achievements.

Our world view changed radically as we began to observe how plate tectonics and other geosystems actually worked. I remember many of the seminal discoveries by the specific AGU sessions in which they were originally presented. The exploration of three-dimensional mantle structure with the reconnaissance tools of predigital seismology made it clear that not all plates are thin and much of the return flow is not shallow, as we had been taught. Instead, the continental cratons have chemically distinct, advectively thickened keels (which I called tectosphere), stabilized for billions of years within a system of deep mantle convection. I have had a great deal of fun watching the vague outlines of this image come into vivid, multicolor focus through seismic tomography.

People like me get awards like this one because we were lucky to be guided by our mentors, helped by our colleagues, and supported by our families and friends. Charles Archambeau, Gerry Wasserburg, and my father (on his way to Vietnam) kept me pointed toward science when many other directions were possible. Don Anderson, my thesis advisor, taught me to go after the big problems; later, as a friendly adversary in the unending battles about the deep structure of continents, the depth of lithospheric slab penetration, and the nature of mantle convection, he surprised me with his flexible, unconventional interpretations of the observations. From Freeman Gilbert, I learned the value of extending the computational tools for model-based inference and, from Bill Menard, the importance of style and romance in scientific research on land and at sea.

I have had the privilege of studying and teaching at some great universities—Caltech, Princeton University, University of California, San Diego, Massachusetts Institute of Technology, and now the University of Southern California. At each of these institutions, my colleagues made doing science fun and productive, and the strong bonds of scientific collaboration cemented many enduring friendships.

Since our first days in graduate school, Bernard Minster and I have explored many aspects of science together, not to mention life in general. My daughter, Alexandra, has continually reminded me why seeking an understanding of our planetary home is so worthwhile, and my wife, Margaret, has added new dimensions to the journey. A host of brilliant and wonderful students, Paul Silver notable among them, taught me as much as I ever taught them; they were comrades in mental expeditions to the unknown. In particular, Stu Sipkin, Ken Creager, and Art Lerner-Lam each played a special role in the research specified in Paul’s generous citation.

As Paul noted, the early times were rather wild, and we lived them to the max. Nearly four decades in the business have furnished my memory with some pretty tall tales, and though my pace has slowed a bit, the adventures still continue. So, to the young scientists in this audience who have traveled to AGU to see what geophysics is all about, I want to emphasize how satisfying a scientific career can be. You should imagine the day when you will be up here accepting some AGU award. You do not have to rush it—the moment will come soon enough—but in the meantime, I hope you will be able to enjoy, as I have done, the exuberance of scientific discovery.

—THOMAS H. JORDAN, University of Southern California, Los Angeles

Francis A. Dahlen, Jr. was awarded the Lehmann Medal at the AGU Fall Meeting Honors Ceremony, which was held on 10 December 2003, in San Francisco, California. The medal honors “outstanding contributions to the understanding of the structure, composition, and dynamics of the Earth’s mantle and core.”



“I feel honored and pleased to cite my friend and Princeton colleague Tony Dahlen for the Inge Lehmann Medal. Given Tony’s wide range of important contributions, there is actually a choice of AGU honors one might cite him for; his influence extends well beyond those fields that are primarily associated with the Lehmann Medal.

“Tony started his scientific journey as an undergraduate at Caltech. By the time he moved on to graduate studies with George Backus and Freeman Gilbert at Scripps he was already applying his many talents to geophysics. He soon pioneered a series of papers on normal modes that represent the first substantial step away from Earth’s spherical symmetry. In fact, all of the current research on the use of low-frequency seismic data for the determination of the Earth’s three-dimensional structure is based on this early work, its extension to an inverse problem, and subsequent research with Martin Smith and John Woodhouse. His interest in the theory of global tomography has survived until this day: recently, he developed a very elegant and efficient theory to include the frequency-dependent effects of diffraction into body wave tomography, a theoretical improvement that was almost immediately rewarded by the imaging of a large number of mantle plumes. These represent the first concrete seismological evidence that many hot spots originate deep in the mantle, confirming Jason Morgan’s long-standing hypothesis.

“Tony’s research into low-frequency seismology led him to investigate the rotation of the Earth; he discovered the excitation mechanism for the Chandler wobble and he quantified the influence of the oceans on rotational variations of the Earth, enabling us to identify those variations that find their cause in the deep interior. In the 1970s, he incorporated prestress, rotation, and self-gravitation into dislocation theory. His research in this area has made him the preeminent scholar in the theory of the free oscillations of the Earth, and resulted in the definitive treatise ‘Theoretical Global Seismology,’ written with Jeroen Tromp.

“It would be wrong, through, to see Tony as a seismologist per se, since he has also made major contributions to geology. With Dan Davis and John Suppe he developed the concept of critical-taper wedge mechanics in the 1980s to explain fold-and-thrust belts and accretionary wedges. This work is arguably one of the most important contributions to the mechanics of mountain belts in the twentieth century and of great relevance for the understanding of earthquakes in such areas. He resolved a petrological controversy regarding equilibrium conditions for a metamorphic reaction under deviatoric stress, showed that the energy dissipation in accretionary wedges is divided roughly equally between basal friction and work against gravity, and was the first to model the role of erosion in the dynamics and thermal evolution of mountain belts, showing it to be a dominant process, a subject of much current interest.

“Tony’s leading position as a scientist was recognized by memberships in the American Academy of Arts and Sciences and the National Academy of Sciences. He was the recipient of a Guggenheim Fellowship and has served the scientific community in too many capacities to list here. No one deserves this year’s Lehmann Medal as much as he does.”

—GUUST NOLET, Princeton University, N. J.


“It is a great honor to accept this 2003 Inge Lehmann Medal from the AGU, and it is a particular pleasure to receive such a flattering citation from my longtime colleague and close friend, Guust Nolet. The Lehmann Medal is given in recognition of ‘outstanding contributions to the understanding of the structure, composition, and dynamics of the Earth’s mantle and core.’ My contribution to this understanding has been modest and indirect: Together with John Woodhouse, the 2001 Lehmann Medalist, I helped to develop a few theoretical tools which John and other seismologists have used to obtain remarkably detailed 3-D images of the Earth’s interior.

“I had a Tom Sawyer childhood in Winslow, Arizona, and was enabled to attend one of our nation’s finest educational institutions, Caltech, by the award of a generous 4-year scholarship—which I assure you was not granted on the basis of my dubious ability as a football player.

“At Caltech, I was exposed to the excitement of forefront geophysical research by legendary but readily available professors, including Jerry Wasserburg, who was prudent enough not to let me near the glassware in his lab. As a graduate student at Scripps, I had the great good fortune to pursue my Ph.D. studies under the supervision of two of the world’s preeminent geophysicists: George Backus, the 1986 Fleming Medalist, and Freeman Gilbert, the 1999 Bowie Medalist. It has been my privilege to work for my entire career at a third great institution, Princeton, where I have witnessed the transformation of a distinguished classical geology department into a modern department of geosciences, encompassing all of the solid-Earth and fluid-Earth disciplines in the AGU.

“During my 33 years at Princeton, I have been blessed with many exceptional graduate students, including Martin Smith, Gordon Shudofsky, Richard Strelitz, Ivan Henson, Peter Davis, Fred Pollitz, Zheng Wang, Li Zhao, Jeroen Tromp, Junho Um, and Henk Keers. I owe a special debt of gratitude to Jeroen, whose shared passion for theoretical global seismology led us to write a 1000-page, 10,000-equation opus on the topic.

“In 1980, I pointed out a minor algebraic error in a preprint on the mechanics of mountain building by Dan Davis and John Suppe, and they graciously invited me to be a coauthor on what is, by far, my most frequently cited paper. I spent most of the next decade elaborating upon the critical Coulomb wedge model, together with Wu-Ling Zhao, Hongbin Xiao, and Terence Barr.

“For the past 7 years, Guust and I have been seeking to improve the theoretical foundations, resolution, and fidelity of seismic tomography, in collaboration with Henk Marquering, Shu-Huei Hung, Adam Baig, Ying Zhou, Raffaella Montelli, and Guy Masters.

“I am well aware that honors such as the Lehmann Medal generally come in the twilight of one’s career, but I am determined to keep laboring in the theoretical trenches and attending AGU meetings, in order to share in the ongoing evolution of our ‘understanding of the structure, composition, and dynamics of the Earth’s mantle and core.’”

—FRANCIS A. DAHLEN, JR., Princeton University, N.J.

John Woodhouse received the Inge Lehmann Award at the 2001 Fall Meeting Honors Ceremony on 12 December, in San Francisco, California. The award is given for outstanding contributions to the understanding of the structure, composition, and dynamics of the Earth’s mantle and core.



“Usually, once you receive the Macelwane Medal, that is it for AGU honors. John Woodhouse is an exception, and even then he has been selected for his second medal sooner than anyone so far. Only 17 years have passed since the meeting in Cincinnati when Freeman Gilbert read the citation for John. But these have been very good years for John and for seismology, in general. Since then, we have produced three-dimensional images of the Earth’s deep interior ranging from the crust to the inner core. We have expanded our global seismographic network from a dreamy design to the reality of well over 100 state-of-the-art stations, most of which transmit data in real time. When John and I were starting the centroid-moment tensor project in 1980, sometimes data from only several stations were available after a wait of 2, sometimes 3, months. Their small dynamic range made the analysis difficult, particularly for large events, when the ground motion exceeded the capacity of the early digital instrumentation. Today, we receive data in real time from over 70 globally distributed observatories, with all events on scale.

“These things are not unconnected. We had the courage to dream, because in the spring of 1983, the time of the earliest planning of the new network, we had the first 3-D models of the upper and lower mantle structure, and it was clear that revolution was in the making. The model of the upper mantle has little changed since then, except for the improved resolution of the details. Models of the lower mantle showed striking upwellings, now called megaplumes, which remained unexplained till today but are certain to be of significance in explaining the behavior of the Earth.

“John Woodhouse received his doctorate in Cambridge, at the famed Department of Applied Mathematics and Theoretical Physics, in 1975. His first contribution that placed him on the ‘fast track’ was a brief paper noting an error in a classical paper by Backus and Gilbert; the error was not in mathematics but in physics. Until 1976, perturbations in normal mode frequencies were calculated using wrong formulae.

“After 2 more years at Scripps and Cambridge, John joined the Harvard faculty in the fall of 1978 as an assistant professor, but he made such rapid progress that he was promoted to full professor in 4 years. From this period came classical papers on coupling of normal modes in an heterogeneous Earth, which paved the way for using splitting of normal modes in 3-D modeling of the Earth’s interior.

“John has a unique gift in his ability to formulate ‘useful theory’; there are few, if any, of his papers that did not lead to important applications in studying the Earth. One such example was the development of the CMT algorithm, and another was an ingenious application of asymptotic properties of normal modes to measuring simultaneously odd and even harmonics of the mantle heterogeneity. Together, these two developments led to a 3-D model of the upper mantle that has been little improved in the last 18 or so years.

“In the landmark year of 1986, John built the first 3-D model of shear velocity of the entire mantle, using splitting functions to derive an even-degree model of the mantle, to show that the large-scale features of heterogeneity are robust over 3 or so decades of frequency. In the same year, he demonstrated that the anomalous splitting of very high phase velocity compressional modes can be explained by anisotropy of the inner core. This was the fiftieth anniversary of its discovery by Inge Lehmann, a very appropriate tribute.

“In 1990, John returned to England to assume a professorship at Oxford. He has built there a leading group in global seismology in Europe, with excellent computational facilities and a complete data archive of global network data. He continues to provide us with fascinating glimpses of the Earth’s deep interior. One hopes that the duties of a department chair will not slow him down.

“With the flood of new data that the U.S. Array project, as a part of Earthscope initiative, will generate, we need John’s skills in developing a better theory, which will be needed to take full advantage of the high-quality, high-density mapping of the Earth’s deep interior. If everything goes well, perhaps there will be another AGU medal for John in 17 years.”

—ADAM M. DZIEWONSKI, Harvard University, Cambridge, Mass.


“Madam President, Ladies and Gentlemen,

“It is a great honor and a great pleasure to receive this award.

“I would like to thank the AGU and the committee, and I also thank my colleagues who must have written quite unreasonable letters.

“To paraphrase Newton, I seem, to myself, to have been playing on the seashore, diverting myself by finding smoother pebbles (for which read tractable problems at long periods) while the ocean of truth lies undiscovered before me. And, of course, there is a vast undiscovered territory in the unknown Earth structure at shorter scale lengths, and also in the properties if seismic waves at shorter periods. A strong motion seismologist, on hearing that I was a long-period seismologist, once said to me ‘Ah—long periods. That is simple,’ to which I responded, immediately on the defensive, ‘Not the way I do it.’As Adam has said, these have been exciting years in the development of ideas about the Earth, and I feel privileged to have been a part of it. It is a particular pleasure tonight that there are many here who are friends and who have, themselves, each made contributions equally deserving of honors. I would like to thank them and to say to them how exciting and rewarding it has been to have been a coworker with you in a great endeavor in this era of dramatic progress.

“There are many factors that have led to these rapid advances. Here I would like to pay tribute to the pioneers of digital seismometry, instrumentation, recording and distribution of data. Albuquerque, IDA, Geoscope, Erlangen have led the way, and IRIS has played a key role in coordinating a global effort, which has truly revolutionized seismology. Let me also pay tribute to the senior seismologists, Adam, of course, prominent among them, who single-mindedly have pursued the vision which has led to this revolution. Peter Medawar said of James Watson, at Cambridge in the 1950s, ‘in addition to being extremely clever, he had something important to be clever about.’ The data streams now available, together with enormous computational resources, give us and future generations of geophysicists, something important to be clever about.

“Medals and honors are sometimes made to mark the end of a long career. I hope and intend that this will not be so in my case. I can take heart from the example of Inge Lehmann. It was only after her retirement at the age of 65, having discovered the inner core some 17 years earlier, that she embarked on the systematic study of upper mantle structure which resulted in the naming of the Lehmann discontinuity in her honor. She was concerned with the regional variation of this feature, and it speaks for her modernity that there are papers at this meeting reporting on this very issue. Trained in mathematics, committed to recording and acquiring data, intimately acquainted with the detailed interpretation of seismograms, Inge Lehmann was a model geophysicist of her own or any other generation.

“It is an honor indeed to receive the Inge Lehmann medal from the American Geophysical Union.”

—JOHN H. WOODHOUSE, Department of Earth Sciences, University of Oxford, U.K.

Richard J. O’Connell was awarded the Inge Lehmann Medal at the AGU Fall Meeting Honors Ceremony, which was held on December 17, 2000, in San Francisco, California. The medal recognizes outstanding contributions to the understanding of the structure, composition, and dynamics of the Earth’s mantle and core.



“Members of the Union, colleagues, ladies and gentlemen, and friends.

“Inge Lehmann was a highly inventive and creative scientist as a young woman and persisted in making outstanding contributions to geophysics, seismology, and Earth structure for over three-quarters of a century. At a time when there were few people in the field and almost no women, she was a singular example of quiet excellence. I often heard of her from Beno Gutenberg and Hugo Benioff. In honor of her contributions, the AGU established the Inge Lehmann Medal for ‘outstanding contributions to the understanding of the structure, composition, and dynamics of the Earth’s mantle and core.’ The quality of an award is really determined by the excellence of the selection committee’s nomination. They have made an excellent choice.

“Rick O’Connell was born in Helena, Montana, the son of a ranching family. I have known him since he arrived at Caltech in 1959 as a physics major. I had the privilege of working with him during his graduate studies where, well before he finished his Ph.D., he had completed a study on the viscosity of the Earth with Don Anderson (1967), and one with me on the dynamics of a phase change (MOHO) that was a whole volume of Reviews of Geophysics (1967). Rick had a combination of unusual traits: 1) a truly deep physical insight into geophysical problems; 2) the good taste to select very important, do-able problems; 3) the ability to carry through and to do an imaginative quantitative analysis without getting lost in the maze, while still respecting nature; and 4) an easygoing, gentle, generous character with good humor.

“Rick was a gentleman cowboy with excellent taste in good food and wines and an abiding interest in art (also with good taste). He did, in those early years, smoke a lot of my cigarettes; but would, after an extensive period of mooching, present me with a carton of cigarettes. Of all the vices enumerated above, the only one he gave up was smoking.

“During his years at Caltech, there was a wonderful comic strip by Stan Lynde called Rick O’Shay. This hero was the modest, gentle, but sharp-shooting, tough and just sheriff of a town in Montana called Conniption-a town of unruly, wild, unkempt inhabitants. Well, Rick O’Connell had his name changed-we all called him Rick O’Shay and he is still Rick O’Shay to me today.

“O’Connell’s pioneering contributions and good taste in the field of geodynamics are world renowned as is his gentle and positive influence as a mentor and colleague of young people in geophysics and the Earth sciences in general. The committee has cited him: for his work on postglacial rebound; for determining that the whole mantle was subject to flow; for his model of the mantle flow associated with plate motions and subduction; for creating a model that globally predicted plate motions in which plate tectonics stir the upper mantle; and for the way he has connected geophysics with geochemistry.

“Madame president, it is a privilege and great personal delight for me to present to you Rick O’Connell, a scholar of great accomplishments and personal grace in a society of sometimes unruly inhabitants. As the recipient of the Inge Lehmann medal, he will, I trust, continue his contributions for the remainder of his 3/4 of a century of science.”

—GERALD J. WASSERBURG, California Institute of Technology, Pasadena, Calif.


“Thank you, Jerry, for your generous and kind remarks.

“When I received the letter from John Knauss informing me that I had been awarded the Lehmann Medal, I was immensely surprised, pleased, and gratified. The study of the Earth’s interior has been mostly the domain of seismologists, who are able to see into the deep Earth. I am pleased that this award has been given for work in geodynamics, and I am honored to represent those who work to relate the Earth’s geologic history to the dynamics of the Earth’s interior.

“Understanding how the Earth works and how the landscapes and seascapes we live in came about has always seemed to me to be an intellectual endeavor that can stand on its own merits, just as exploring the stars does. I have been lucky to be able to follow my interests throughout my life, pursuing understanding of how the Earth works.

“I grew up in Montana, where I had many opportunities to marvel at the magnificent mountains, valleys, and plains-occasionally while sitting on a horse as the Sun came up. Fortunately, my parents were supportive and allowed me to seek answers to how things worked, even at the risk of an explosion in my basement laboratory. They would have been especially gratified by this award.

“They also encouraged me to see a world beyond my father’s ranch, and, prompted by the first snowfall of September, I went to Caltech to study physics. There, Jerry Wasserburg showed me that studying the Earth was just another application of physics, and an unusually interesting one at that.

“Jerry later persuaded me to come back to graduate school at Caltech after I had taken a year off and seen a bit of the world. He showed me the difference between following curiosity and choosing the most promising problem to pursue. Jerry started me on a geodynamical problem-I later learned that the Moho is not a phase change, but I really learned how to construct a model to figure out what such a phase change would do. In the process, Jerry’s broad interests and joy of doing science, and, I hope, a bit of his intellectual style, rubbed off on me.

“As a postdoc, I was again given the opportunity to follow new interests. I had previously worked on post-glacial rebound of the whole Earth, but Don Anderson (with Hartmut Spetzler’s expert guidance) let me discover the fun of laboratory work, measuring high-pressure elastic properties and satisfying my desires to take things apart and then figure out how to put them back together.

“When Ray Siever recruited me to Harvard, I once again found opportunity, inspiration, and superb colleagues, both inside and outside the geology department. One day, Bernie Budiansky walked into my office, and I had the chance to explain geophysics to a first-rate intellect and a person who became a close friend. In return, he taught me mechanics and how to figure out the elastic properties of real rocks. In the mid-1970s, the dynamics of plate tectonics seemed the most important and challenging problem. A seminar with Geoff Davies and Brad Hager (among others) sent us all into geodynamics for good. At the same time, Adam Dziewonski started imaging lateral mantle structure, and the profound confluence of seismology and geodynamics really began.

“During one of those humbling moments-reading reviews of a proposal that didn’t make it-I noted that one reviewer acknowledged that ‘… at least the PI’s students had done good work.’ About that he was right; I have been lucky to work with outstanding students. Brad Hager was the first (I couldn’t have had a better one), and I now interact with his academic progeny, through several generations; I continue to learn from my current students. Throughout my career I have always tried to give my students the same encouragement and freedom to pursue their interests that I have had. As was said about a young Julian Schwinger, ‘The best guidance for such outstanding students is to leave them to their own devices.’

“I am lucky to have the love and understanding-and forbearance-of my family, and I am extremely pleased that they are here tonight. My son Brian is here with his wife Claudia. He has been with me from Caltech to Harvard, with meetings and sabbaticals in between. He has always been a source of good humor, sense, and perspective, and an inspiration for going through life and overcoming difficulties with grace. My wife Susan has good-naturedly adapted to sharing a life with a scientist who is frequently distracted and has horrible work habits. She also taught me about sailing on Buzzards Bay and makes my life more fun than it deserves to be. My stepdaughter Lily shared my commute for several years; I miss her company and the new perspective she brought me.

“I’ve been lucky in my opportunities and in having support from those who allowed and encouraged me to pursue them, as well as in having good colleagues and good students. They all share this award.”

—RICHARD J. O’CONNELL, Harvard University, Cambridge, Mass.

Donald Helmberger was awarded the Inge Lehmann Medal at the AGU Fall Meeting Honors Ceremony, which was held on December 10, 1997, in San Francisco, California. The Lehmann Medal is given in recognition of outstanding contributions to the understanding of the structure, composition, and dynamics of the Earth’s mantle and core.



“One century ago, on June 12, 1897, the great Assam earthquake occurred. It was thoroughly investigated by R. D. Oldham, who was the head of the Geological Survey of India. Oldham used recordings of the earthquake to identify clearly for the first time the S wave and to prepare the first travel time tables for P waves and S waves. Thus began the use of seismological data to infer the internal structure of the Earth. Subsequently, in 1906, Oldham deduced the existence of the fluid core. Gutenberg published his determination of its radius in 1915 and Lehmann discovered the inner core in 1935. Her discovery is the primary basis for the establishment of the award in her name.

“In the late twentieth century it was discovered that the inner core is solid, that it is anisotropic, and that it has a dissipative zone just beneath the inner core boundary. Furthermore, it seems to rotate slightly faster than the rest of the Earth. For the outer core and the base of the mantle it has been discovered that there are patches of very low shear modulus just above the outer core boundary and that the outer core is very nearly a perfect fluid. The cores of the Earth play the major role in the generation of the Earth’s magnetic field and contribute prominently to variations in the length of day. The study of the Earth’s cores has become a major branch of geophysics, the seismological components of the study being dominated by Don Helmberger and his students and postdoctoral fellows. His contributions are manifold, quantitative, and durable. For all that he has accomplished he has been chosen to be the first recipient of the Inge Lehmann Medal of the American Geophysical Union.

“It is usually considered to be bad luck to be a younger member of a large family. One’s older siblings tend to smother one’s individuality. There are exceptions, though. One was Benjamin Franklin, who was preceded by 14 brothers and sisters. Another is Don Helmberger, the youngest of a baker’s dozen. Don grew up in a Catholic family in Minnesota and received his undergraduate education there.

“As a Ph.D. student at the Scripps Institution of Oceanography, Don was supervised by Russell Raitt and me. Don’s performance was a pleasure to us. He used the excellent marine seismic data collected by Russ and carefully archived at Scripps and the method of generalized ray theory for computing synthetic seismograms to produce a Ph.D. thesis that, in retrospect, was considerably ahead of the times. Don, more than anyone else, pioneered quantitative seismology: the comparison of realistic, computed seismograms with observed data to infer deep Earth structure.

“Don’s tenure at the California Institute of Technology has been marked by a sequence of major accomplishments, and he is being honored here for those that relate to the Earth’s cores. Yet it is very important to emphasize that Don is a superb teacher and trainer of research students, as well. His graduates have populated the faculties of the best universities in the country and a handful of them have won the AGU Macelwane Medal. I know that Don is quietly proud of them, just as I am proud of him.

“If Don’s bibliography were restricted only to his contributions to the structure of the Earth’s cores, it would be a tribute to any geophysicist. Those of us who know Don are aware that there is much more than that restricted list. His work on the structure of the crust and upper mantle and his studies of earthquake source mechanisms, very important to the comprehensive test ban treaty, attest to the range of this gifted scientist. To tell more now would be to exceed the scope of this citation. So, we must await another occasion, another time, perhaps another award, to learn more about the career of Donald Vincent Helmberger, Inge Lehmann Medalist.”

—J. FREEMAN GILBERT, University of California, San Diego


“Thank you, Freeman, for your generous remarks and to all of you who have earned this award for me. I am delighted to receive this medal on behalf of all of us wiggly line lovers.

“It is traditional for medalists to describe the particular case of circumstances and good luck leading to their careers. In my case, it is serendipity cubed, having been raised on the shores of Lake Wilbegon (about halfway between Fargo and Brainerd). Recently, I have discovered that Gary Glazmeier was born on the opposite shore, and he too must have observed the Northern Lights and other strange optical phenomenon associated with very cold climates. Perhaps, we both dreamed of studying such stuff, which leads one to think of a rotating core? Or maybe, just some other place that is warmer than Minnesota? I don’t remember, except dreaming is what I do best.

“In the summer of 1960, a cruise to the North Pacific and the Bering Sea, called Leapfrog, provided my first big opportunity to see the Earth without snow on it. George Shor and his wife, Betty, also introduced me to Scripps hospitality at its finest, something totally different than the culture at a 30K university. He and Russ Raitt (a remarkable man) slipped me through the back door of University of California at San Diego as one of their first graduate students. Russ did his Ph.D. work under Millikan at the California Institute of Technology and approached marine geophysics quite differently than other people in the exploration business. He conducted research in the ocean as if it were a laboratory, no easy task as I quickly learned (100-knot winds, etc.). The pressure history of each shot was measured and logged, the recording system calibrated in absolute strengths, and all assembled nicely into operator form. After taking Freeman’s course in theoretical seismology, it was easy to construct synthetics by simply performing convolutions, since they did all work.

“My next good fortune was meeting Frank Press, who offered me a postdoc at the Massachusetts Institute of Technology. There, Nafi Toksoz introduced me to real seismograms and deep Earth structure. Ralph Wiggins and I started modeling upper mantle triplications with this data, which seems to have set the course of my career.

“After a year at Princeton, I joined the Seismology Lab at Caltech. Team teaching with Dave Harkrider, looking at seismograms with Hiroo Kanamori, and trying to keep up with Don Anderson’s triple puns have been most interesting, but working with talented graduate students has been the most rewarding.

“Thank you all for sending your best students to Caltech. Keep it up, and I promise to use the new broadband data to sharpen some of our crude images and perhaps, to image a plume all the way from the core-mantle-boundary to the surface (dream).”

—DONALD HELMBERGER, California Institute of Technology, Pasadena

Honors Contacts

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