NS33A-01 INVITED
Near-Surface Geophysics: Advancing Earth Science Through Advances in Imaging
The near-surface of Earth (the top $\sim$100 m) is the region that supports human infrastructure, provides water and mineral resources, and is the interface between solid Earth and atmosphere for many of the biogeochemical cycles that sustain life. Developing an understanding of the processes and properties that occur here is essential for advancing our understanding of many parts of the Earth system. Yet our ability to study, sample, or probe this zone is remarkably primitive. Many investigations rely on drilling, trenching, and direct sampling. But given the pervasive spatial heterogeneity of the region, such methods yield information that is inadequate in terms of the spatial extent and density of sampling. As a result, the Earth science community is turning to geophysical imaging. The area of research that is focused on developing and applying geophysical methods to study this region of Earth is referred to as near-surface geophysics. Near-surface geophysics, as an area of research, includes many types of research, and many types of researchers. Some researchers are drawn to near-surface geophysics due to an interest in specific properties, processes, or applications, which can range from applied to basic science. As examples, near-surface geophysical methods are used for resource exploration and extraction, for the characterization of contaminated sites, for the assessment and design of built infrastructure; and to address scientific questions in neotectonics, volcanology, glaciology, hydrology, sedimentology, archaeology, geochemistry and biogeochemistry. Other researchers are drawn to near-surface geophysics due to an interest in the science of imaging as the driving scientific question. Advances in imaging require investigating the ways in which physical sensors can (or cannot) capture the complexity of a natural system, determining how best to quantify and enhance the spatial and temporal resolution of a measurement, developing new methods for the inversion of geophysical data to obtain an Earth image, and finding ways to transform that image to reveal new information about processes and properties. Near-surface geophysics brings together the science of imaging with the science of Earth; so challenges us to move forward in an integrated way to advance both imaging methods and Earth science.
NS33A-02 INVITED
Application of Geophysical Techniques in Glaciology
Glaciologists are faced with the problem that most processes that control ice motion or the transport of water and sediment occur either deep within the glacier ice or at the interface between it and the underlying substrate. However, glaciers are an ideal environment for the application of many geophysical techniques and they have led to significant advances in our understanding of glaciers and ice sheets. Surface and airborne radar has a long pedigree in glaciology and has been used extensively to map beds of the major ice sheets and isochrones within the ice. Cold ice, such as that in Antarctica is easy for radar energy to penetrate, but the water in warm ice scatters radar energy. For this reason it has proved more difficult to image the beds of outlet glaciers in Greenland. Recent advances, particularly in ground-penetrating radar, have meant that it has been possible to image sediment structures within the ice and to use the reflectivity at the bed capture some aspects of the basal water system. Radar energy does not normally penetrate into the beds of ice masses - which are often wet sediments. However, reflection seismics allows us to image further into the basal environment. Using the impedance contrast across the basal interface it is possible to determine whether basal sediments are frozen or unfrozen, and whether they are actively deforming or the ice is sliding over the bed. These questions are key in understanding the dynamics of an ice mass. As a glacier moves overs its bed, seismic energy can be released that provides information on the nature of the basal environment. These events record different source types and relative friction between regions of the bed (so-called "sticky" and "slippery" spots). Considerable work is required to fully exploit the potential of this technique which requires integration with GPS measurements, locating events, and modeling of source types. Geophysical techniques are an ideal tool for exploring the inaccessible environment beneath ice masses. In this presentation I will outline some of the successes of their use and identify areas where their continued exploitation has great potential.
NS33A-03 INVITED
Improving understanding of volcanic processes and hazards with near-surface geophysics
Near-surface geophysical techniques have become integral tools for addressing a variety of volcanological problems, in particular for better understanding of processes and hazards associated with explosive volcanism. Processes with near-surface signatures can be examined with an array of high-resolution methods that offer imaging capabilities dramatically beyond traditional larger-scale gravity, magnetic, and seismic studies. Recent high-resolution surveys with self-potential (SP) and electromagnetic (EM) methods shed light on fluid flow and degassing processes. Time-domain EM surveys yield remarkable constraints on near-vent water table depths and associated hydrogeologic processes, in terrains where drilling would be prohibitively expensive. Very low frequency (VLF) electromagnetic methods have been used to image near-vent fracture systems, and in some cases to image magmas in the shallow subsurface directly. Resistivity methods, useful in geothermal exploration, are less well-suited to mapping the highly resistive near-surface of young volcanoes. Ground penetrating radar (GPR) surveying, on the other hand, works best in resistive strata and can offer high-resolution 2- and 3-D stratigraphic images in otherwise inaccessible settings. GPR studies can provide constraints on tephra fall and surge deposit volumes and internal structure, the nature of paleosols separating individual eruption deposits, and volcanic block distributions. Microgravity studies illuminate near- surface density changes. Electromagnetic and magnetic instruments in particular can be deployed from helicopters for rapid, high-resolution, and repeated surveying. Finally, the application and cross-correlation of multiple methods is emerging as an essential way to characterize active volcanoes and volcanic processes.
NS33A-04 INVITED
Biogeophysics: A New Frontier for the Geophysical Community
Attempts to understand the role of microbes in altering the physical properties of geologic systems has resulted in the development of a new sub discipline in geophysics called biogeophysics, which breaks the traditional barriers between geomicrobiology, biogeochemistry, and geophysics. Biogeophysics investigates the interaction between microorganisms and subsurface geologic media, and possibly the direct geophysical detection of microbes and microbial cell concentrations. Research in this sub discipline presents a potential for the development and utility of geophysical techniques to measure not only the subsurface physical and chemical properties, as geophysics is conventionally used, but also the properties related to biological activity, processes, and interactions. This new field provides exciting new frontiers for training the next generation of multidisciplinary research scientists and permits geophysics to be interfaced with research in Biogeosciences. This presentation will provide an overview of laboratory and field investigations completed in this new field of biogeophysics and their potential applications in astrobiology, geomicrobiology, biogeochemistry, microbial enhanced oil recovery, and remediation studies.