Fault Trace and Slip in the 2008 Mw 7.9 Sichuan, China Earthquake From InSAR Observations

Details Fault Trace and Slip in the 2008 Mw 7.9 Sichuan, China Earthquake From InSAR Observations Fault Trace and Slip in the 2008 Mw 7.9 Sichuan, China Earthquake From InSAR Observations

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.g33c0714l&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #G33C-0714

Other

1209 Tectonic Deformation (6924), 1240 Satellite Geodesy: Results (6929, 7215, 7230, 7240), 1242 Seismic Cycle Related Deformations (6924, 7209, 7223, 7230), 6924 Interferometry (1207, 1209, 1242), 7212 Earthquake Ground Motions And Engineering Seismology

Scientific paper

The 2008 Mw 7.9 Sichuan, China earthquake was one of the most devastating events in recent times, and claimed more than 80000 lives. Six adjacent pairs of ascending ALOS PALSAR images and three independent pairs of descending ENVISAT ASAR images were processed for both interferograms and SAR pixel offsets. Three additional pairs of ENVISAT ASAR wide-swath (ScanSAR) interferograms were also processed. In the rugged terrain and heavy vegetation of the Longmen Shan, coseismic deformation signals cannot be resolved by the C-band interferograms, although there is some coherence in the flat plains and less steep areas further into the plateau; In contrast, coherence at L-band is generally good and deformation is well resolved. This highlights the main advantage of L-band over C-band, i.e. less temporal decorrelation due to its capability to penetrate more deeply in vegetation. The shallower 38° incidence of PALSAR also helps in the high-relief areas. No useful signals can be resolved in either C-band or L-band interferograms within c.5-30 km along the faults because the large deformations of more than one pixel cause localized misregistration. SAR pixel offsets provide an unambiguous measurement of the surface displacement, and the presence of macroscopic surface features such as ridges, lake shorelines or roads often make the technique successful even in incoherent regions. Both our PALSAR and ASAR offset maps clearly show the fault trace of this large event, and their patterns are nicely consistent with each other, however the PALSAR along-track offsets are heavily contaminated with large wavelike features that are likely due to transient ionospheric disturbances. Based on InSAR observations, we model the large event with four sub-faults: (1) the strikes and lengths of the sub-faults are determined using offset maps; (2) the fault geometries are estimated using interferometric phases and range offsets with the strikes and lengths fixed; (3) fault slip is re- determined with fixed fault geometries. It appears that our preliminary models can explain more than 90% of the observed deformation signals, suggesting the average slips in the northern sub-faults were smaller than those in the southern one. The latter had a significant thrust component and the other segments had predominantly right-lateral slip. Note: (1) COMET: Centre for the Observation and Modelling of Earthquakes and Tectonics; (2) The first three co-authors are in alphabetical order.

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