AGU journal highlights -- Aug. 1, 2007

Authors: Edmund K. M. Chang and Yanjuan Guo: Institute for Terrestrial and Planetary Atmospheres, Marine Sciences Research Center, Stony Brook University, Stony Brook, New York, U.S.A.

Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL030169, 2007

4. Satellite gravity measurements detect deformation from Sumatra-Andaman earthquakes

Satellite gravity measurements, which have been used to estimate changes in groundwater storage, sea level, and polar ice sheet extent, can also provide a unique way to monitor deformation associated with major earthquakes, supplementing global positioning system measurements which are limited if earthquakes happen off shore. Chen et al. used data from the Gravity Recovery and Climate Experiment (GRACE) to observe and study the effects of seismic deformation due to ruptures from the magnitude 9.3 Sumatra-Andaman earthquake on 26 December 2004 and its companion Nias Earthquake (magnitude 8.7) on 28 March 2005. Through improved filtering methods and more refined processing of GRACE data, the authors find that gravity field disturbances caused by these earthquakes extend over 1800 kilometers (1100 miles) along the Andaman and Sunda subduction zones, and that these disturbances change with time following the earthquake. The authors expect that gravity changes are due to afterslip, viscous relaxation of the upper mantle, or other processes associated with upper mantle recovery after such great earthquakes.

Title: GRACE detects coseismic and postseismic deformation from the Sumatra-Andaman Earthquake

Authors: J. L. Chen and B. D. Tapley: Center for Space Research, University of Texas at Austin, Austin, Texas, U.S.A.;

C. R. Wilson: Center for Space Research, University of Texas at Austin, Austin, Texas, U.S.A.; Department of Geological Sciences, University of Texas at Austin, Austin, Texas, U.S.A.;

S. Grand: Department of Geological Sciences, University of Texas at Austin, Austin, Texas, U.S.A.

Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL030356, 2007

6. Ocean supergyre in southern hemisphere

Mid-latitude oceanic circulation in the southern hemisphere is traditionally thought to consist of distinct, basin-wide, circular currents, or gyres, contained within the Indian, Pacific, and Atlantic oceans. However, model simulations suggest that these gyres are linked by a global-scale 'supergyre' that transfers water to all three ocean basins. From a thorough analysis of temperature and salinity profiles collected since 1950 between 60°S and the equator, Ridgway and Dunn locate this supergyre. Water flows at intermediate depths from the Pacific to the Indian Ocean through a pathway around Tasmania, an observation supported by models but not fully documented by previous field research until now. Consistent with previous observations, the authors find that in the upper layers, Pacific Ocean water principally flows through the Indonesian archipelago into the Indian Ocean. Water from the Indian Ocean then leaks into the Atlantic Ocean around the southern tip of Africa. A pathway on the northern edge of the Antarctic Circumpolar Current returns the gyre waters back to the Pacific. The supergyre is a central agent for distributing intermediate water around the global ocean.