5. Tracking earthquake motion with GPS at finer timescales
After a large earthquake, a fault continues to creep aseismically, resulting in measurable ground deformation. Typically, such postseismic motions are measured with Global Positioning System (GPS) receivers. In order to reduce intrinsic GPS noise for these studies, most scientists average all GPS data collected within 24-hour spans. Miyazaki and Larson note that these 24-hour averages make it impossible to separate seismic deformations from the initial aseismic deformations. They study the 2003 Tokachi-Oki event, where the ground signal was further complicated by the rupture of a large aftershock (magnitude 7.4) about an hour after the main shock (magnitude 8). By reducing GPS noise, the authors estimate the displacements due to both earthquakes, along with aseismic motions in the first few hours. By inverting the measurements of surface deformation, they find that slip between the two earthquakes occurred between the two epicentral regions, possibly triggering the aftershock. The authors expect that higher sampling rates for GPS solutions will help scientists gain greater insight into studies of slip propagation and stress transfer.
Title: Coseismic and early postseismic slip for the 2003 Tokachi-Oki earthquake sequence inferred from GPS data
Authors: Shin'ichi Miyazaki: Earthquake Research Institute, University of Tokyo, Tokyo Japan;
Kristine M. Larson: Department of Aerospace Engineering Sciences, University of Colorado, Boulder, Colorado, U.S.A.
Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL032309, 2008; http://dx.doi.org/10.1029/2007GL032309
6. Atlantic sea-surface temperatures affect Indian monsoon
The Indian monsoon is strongly influenced by El NioSouthern Oscillation (ENSO) patterns on interannual timescales, with a drie
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American Geophysical Union