1. Linking water content with seismic velocity
2. Tunnel samples provide evidence of fault characteristics
3. Ancient quake history revealed in Roman ruins
4. Special section on climactic Atlantic variability
5. Carbon sequestration may adversely affect deep sea life
6. Distinguishing climate controls at the equator
7. New model for fluid-filled fault zones
8. Dynamic strain from earthquakes increases stream flow
9. Calculating ice thickness on Europa
10. Seasonal water melting may have eroded Martian dunes

A new model that can be used to estimate the water content in the Earth's mantle using seismic-wave velocities may shed new light on earthquake seismicity and volcanism in subduction zones. Carlson and Miller present the first study relating the amount of water stored in partially serpentinized peridotites to seismic-wave velocities measured in the laboratory. Serpentine, a mineral that contains appreciable water in its structure, forms from peridotite, which is a rock commonly found in Earth's upper mantle. The partially serpentinized rock is an efficient method of transporting water to the mantle in subduction zones, where the liquid can affect earthquake seismicity and the formation of ash and melted material ejected from volcanoes. The authors estimated the wave speed through the deep-underground materials and show that a slight decrease in wave velocity reflects an increase in the water (and serpentine) content in the rocks below.

Title: Mantle wedge water contents estimated from seismic velocities in partially serpentinized peridotites

Authors:
Richard L. Carlson, D. Jay Miller, Texas A & M University, College Station, Texas.

Source: Geophysical Research Letters (GRL) paper: 10.1029/2002GL016600, 2003

Rock samples taken from a tunnel that runs through an active fault zone in Japan have provided evidence to indicate the structure and hydrogeology of the fault. Forster et al. examined rocks from boreholes deep within the Active Fault Survey Tunnel in Japan and used data from the fault's fluid content to infer the permeability and porosity within the Mozumi-Sukenobu fault. Such measurements, including a chlorofluorocarbon analysis to estimate the age of the water entering the tunnel through the zone's porous rocks, can help researchers better understand the fault's hydraulic structure and estimate the conditions leading up to an earthquake. Their results support the hypothesis of a fluid-saturated fault zone model that contains an interlayered sequence of low-velocity porous and non-porous rocks that weakens seismic waves generated by earthquakes.

Title: Hydrologic properties and structure of the Mozumi Fault, central Japan

Authors:
Craig B. Forster, University of Utah, Salt Lake City, Utah;
James P. Evans, Ronald Jeffreys, Utah State University, Logan, Utah;
Hidemi Tanaka, University of Tokyo, Tokyo, Japan;
Tsuyoshi Nohara, Japan Nuclear Cycle Development Institute, Jorinji, Izumi, Tokishi Gifu, Japan.

Source: Geophysical Research Letters (GRL) paper: 10.1029/2002GL014904, 2003

An analysis of ancient archaeological remains in southern Italy believed to be Hercules's sanctuary indicates that earthquakes and tremors along a nearby fault line likely affected Romans dating back to the 3rd century BCE. Galli and Galadini examined the ruins of structures destroyed by seismic activity over the centuries and found that estimating the date of the collapsed structures can provide an accurate measure of the region's seismological history. The authors also used the historical information to determine the slip rate since the original sanctuary was destroyed and identified the parameters of an active fault system, which was responsible for other strong earthquakes in the recent past. Their study indicates that earthquakes along the fault line affected the life and building plans for ancient Romans, who had to deal with the same earthquake hazards as in present times.

Title: Disruptive earthquakes revealed by faulted archaeological relics in Samnium (Molise, southern Italy)

Authors:
Paolo Galli, Seismic Survey of Italy, Rome, Italy;
F. Galadini, National Research Council, Rome, Italy.

Source: Geophysical Research Letters (GRL) paper: 10.1029/2002GL016456, 2003

The 1 March issue of Geophysical Research Letters features a collection of papers about climactic tropical Atlantic variability collected during workshops known as the CLIVAR series. The papers were presented during a pair of conferences in 1999 and 2001 to address the science behind the oceanic changes, including efforts to expand and coordinate international observational programs in the tropical latitudes. Garzoli and Servain summarize the research efforts to date to analyze and predict the phenomenon, which is similar and perhaps connected to the El Nino effects and the North Atlantic Oscillation patterns that drive sea surface temperature and climactic changes in the oceans. Such weather circulation patterns directly affect the climate of parts of North, Central and South America, Africa, and the Caribbean. The special section on CLIVAR also includes studies of the rainfall, ocean water currents and circulation, and the atmosphere-water connections in the Atlantic region.

Title: CLIVAR workshop on tropical Atlantic variability

Authors:
Silvia L. Garzoli, National Oceanic and Atmospheric Administration/Atlantic Oceanographic and Meteorological Laboratory, Miami, Florida;
Jacques Servain, Foundation for Meteorology and Water Resources of Ceara State (FUNCEME), Fortaleza, Ce, Brazil.

Source: Geophysical Research Letters (GRL) paper: 10.1029/2002GL016823, 2003

Injecting significant amounts of carbon dioxide into the deep ocean may reduce the amount of the gas in the atmosphere, but will likely affect surface and deep underwater marine life. L. D. Danny Harvey assessed the impact on surface water acidity and carbonate concentrations for various carbon dioxide-injection scenarios in either deep geological reservoirs or in the deep ocean. Carbonate is a vital part of coral reefs and of many microorganisms in the marine food chain. Harvey's analysis examined the effects from models that simulated an increase, a decrease and unchanged quantities of carbon dioxide production, along with improved methods to capture the gas before its emission into the environment, compared to the present rate of carbon dioxide emissions. He found that sequestration would be a useful method of mitigating carbon in the atmosphere only when paired with other carbon dioxide reduction methods, including major reductions in fossil fuel use.

Title: Impact of deep-ocean carbon sequestration on atmospheric CO2 and on surface-water chemistry

Author:
L. D. Danny Harvey, University of Toronto, Toronto, Ontario, Canada.

Source: Geophysical Research Letters (GRL) paper: 10.1029/2002GL016224, 2003

A coupled ocean-atmosphere model study shows that weather conditions outside the tropics affect the climate at the equator as much as the tropical circulation patterns. Liu and Yang found that ocean water warming observed in the tropics is caused by current-induced extratropical water circulation variations, an oceanic "tunnel" of overturning waters, and an atmospheric "bridge" of overturning circulation. The authors suggest that such  an oceanic tunnel is the major source of underwater temperature increases near the equator, while the atmospheric bridge stimulates surface water temperature changes there. They report that, for example, a 2 degree Celsius [4 degree Fahrenheit] warming in the sea surface temperature from outside the tropical regions produces a 1 degree Celsius [2 degree Fahrenheit] increase in the surface and subsurface equatorial ocean temperature. The study is the first to distinguish specific causes for changes in tropical conditions from the non-tropical atmospheric environment and helps to establish the cause of water temperature changes in the tropical seas.  Title: Extratropical control of tropical climate, the atmospheric bridge and oceanic tunnel.

Authors:
Zhengyu Liu, Haijun Yang, Center for Climatic Research, University of Wisconsin-Madison, Wisconsin.

Source: Geophysical Research Letters (GRL) paper: 10.1029/2002GL016492, 2003

Researchers have created a new earthquake model that explains the unprecedented ground motion during a massive quake in Taiwan as the result of fluid lubrication within the fault zone. Ma et al. suggest that lubrication from a viscous fluid within the fault zone could explain the fastest-ever ground motion ever recorded following the Chi-Chi temblor in 1999. The authors found that the northern and southern ends of the fault line exhibited opposite behavior, with the northern end showing large ground velocities, including rapid land movement of 4.5 meters [15 feet] per second, with very little ground displacement. The southern end, however, had significant ground slip and rupture combined with slightly below average ground movement velocity. The authors provide a model that can be used at the site and propose a model where fluid dynamics within the fault explains the earthquake motion and may help explain similar ground movements in the past.

Title: Evidence for fault lubrication during the 1999 Chi-Chi, Taiwan, earthquake (Mw 7.6)

Authors:
Kuo-Fong Ma, Institute of Geophysics, National Central University, Taiwan;
Emily E. Brodsky, University of California-Los Angeles, California;
Jim Mori, Disaster Prevention Research Institute, Kyoto University, Japan;
Chen Ji, Teh-Ru A. Song, Hiroo Kanamori, California Institute of Technology, Pasadena, California.

Source: Geophysical Research Letters (GRL) paper: 10.1029/2002GL015380, 2003

The ground movement during an earthquake is responsible for changes in the stream flow in a California creek and is the likely cause of increased flow in similar creeks worldwide following quakes. Manga et al. analyzed a history of seismic activity at Sespe Creek in southern California and found that dynamic strain from seismic waves caused the increase in its water flow after large tremors. The watershed experiences significant seismic activity, including more than 50 quakes with a magnitude of 5.0 or higher in the past 100 years, and has seen significant increases in stream flow following three large quakes during that time. The authors found that the observed stream changes have been similar and that while static changes from permanent ground movement caused some flow increases, the seismic waves are the dominant source of the flow increase.

Title: Response of streamflow to multiple earthquakes

Authors:
Michael Manga, Michael Boone, University of California-Berkeley and Lawrence Berkeley National Laboratory, Livermore, California;
Emily E. Brodsky, University of California-Los Angeles, California.

Source: Geophysical Research Letters (GRL) paper: 10.1029/2002GL016618, 2003

A new measurement of the ice thickness on Jupiter's moon Europa estimates the depth of the icy crust and provides a third independent assessment of the satellite's ice shell, allowing researchers a combined method to project its actual depth. Nimmo et al. analyzed topographic images taken near a deep crater on Europa's surface by the Galileo spacecraft and inferred the rigidity of the ice to estimate the ice thickness in the region. The moon is thought to have a liquid water ocean beneath the ice layer that
could potentially contain living organisms, but scientists have not definitively determined how deep a spacecraft would have to burrow to reach the water. The authors conclude that the ice sheet thickness is at least 15 kilometers [9 miles] and most likely approximately 25 kilometers [16 miles] deep and distributed uniformly over the entire satellite. 

Title: Estimates of Europa's ice shell thickness from elastically supported topography

Authors:
Francis Nimmo, University College London, London, United Kingdom;
B. Giese, German Center for Earth and Space Studies, Berlin, Germany;
R. T. Pappalardo, University of Colorado, Boulder, Colorado.

Source: Geophysical Research Letters (GRL) paper: 10.1029/2002GL016660, 2003

Erosion along a Martian dune slope may be caused by seasonal melting of water ice normally frozen within the fine-grained surface material. Reiss and Jaumann suggest that satellite images taken of the high walls of a dune field on Mars indicate that the formations were created by surface material flow similar to mudslides on Earth. Their analysis shows frost forming at various times on the planet's surface, leading them to estimate that liquid water could become stable for a limited time during the summer in the southern hemisphere. The explanation offers an alternative to theories that propose that frozen carbon dioxide may have produced the flows or that geothermal heating could have reached the surface in the past. Because the seasonal melting would only affect the top few centimeters [inch or two] of the land, the researchers conclude that the dune formations formed over several years of freeze-thaw cycles.

Title: Recent debris flows on Mars: Seasonal observations of the Russell Crater dune field

Authors:
Dennis Reiss, R. Jaumann, Insitute of Space Sensor Technology and Planetary Exploration, German Aerospace Center (DLR), Berlin, Germany.

Source: Geophysical Research Letters (GRL) paper: 10.1029/2002GL016704, 2003
 

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