HR: 09:00h
AN: G51D-05 INVITED     [Abstracts]
TI: Geodetically Observed Temporal Variation of Crustal Deformation in Southern California and Northern Rim of Tibet
AU: * Shen, Z
EM: zshen@ies.ac.cn
AF: Institute of Geology, China Earthquake Administration, P.O.Box 9803, Qijiahuozi, Beijing, 100029 China
AU: * Shen, Z
EM: zshen@ies.ac.cn
AF: Dept of Earth and Space Science/UCLA, 3806 Geology, 595 Charles Young Drive, Los Angeles, CA 90095-1567 United States
AU: Zeng, Y
EM:
AF: US Geological Survey, 1711 Illinois Ave, Golden, CO 80401 United States
AU: Jackson, D D
EM:
AF: Dept of Earth and Space Science/UCLA, 3806 Geology, 595 Charles Young Drive, Los Angeles, CA 90095-1567 United States
AB: It has been recognized that geologically and geodetically estimated tectonic strain rates often differ from each other. The discrepancy is considered a result of temporal variation in tectonic deformation. Examples of the most common temporal variations are coseismic and postseismic deformations during an earthquake cycle. Fault interactions associated with large earthquakes also result in temporal variation of the deformation field. This is evident by our geodetic measurements in southern California and along the northern Rim of Tibet. During our analysis of the SCEC Crustal Motion Map v3.0, we compared the deformation fields between two time periods of 1980-1992.5 before and 1993-2001 after the 1992 Mw7.3 Landers earthquake. The data of the two time periods are used to invert for fault slip rates in the region. The results show that fault slip rate along the San Andreas fault was increased from 27 mm/yr to 31 mm/yr along the Carrizo Plain section, decreased from 20 mm/yr to 16 mm/yr along the Mojave section, and increased from 20 mm/yr to 24 mm/yr along the Coachella Valley section, respectively. The slip rate changes are consistent with the Coulomb stress changes caused by the earthquake. It brings the post-Landers fault slip rates along the San Andreas fault closer to their geological estimates for the Carrizo Plain and Coachella Valley sections, and away from the geological estimate for the Mojave section, respectively, suggesting significant modulation of the deformation field by the earthquake stress transfer. At the northern Rim of Tibet we derive a right lateral slip rate of 9 mm/yr along the central section of the Altyn Tagh fault, using GPS data observed during 1994-1998. Our recent result places the slip rate at the same section of the fault at about 6 mm/yr using GPS data observed in 1999-2004. Both rates are significantly slower than their geological estimates of around 20 mm/yr. Two M7 earthquakes occurred south of the fault during these time periods may have affected the deformation field in the region. The 1997 Mw 7.6 Manyi earthquake occurred about 400 km southwest and the 2001 Mw 7.9 Kokoxili earthquake occurred about 300 km southeast of the fault, respectively. Modeling of the stress field resulted from the coseismic and postseismic deformation shows decrease (~0.1 bars) in Coulomb stress along the fault during and after both events. Thus the slow fault slip rates could be caused by the decreases in regional stresses induced by those large earthquakes. We are in the process of further modeling the effect of these fault slip rate changes and the result will be reported at the meeting.
DE: 1240 Satellite geodesy: results (6929, 7215, 7230, 7240)
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8163 Rheology and friction of fault zones (8034)
SC: Geodesy [G]
MN: Fall Meeting 2005