Rapid Imaging of Large Earthquake Rupture Zones with P waves - Figure 1

Rapid Imaging of Large Earthquake Rupture Zones with P waves: Application to the 28 March 2005 Sumatra Mw 8.7 Earthquake Suggests Bilateral Rupture Figure 1. Images of back-projected P-wave energy for the March 28, 2005, Mw = 8.7 Sumatra earthquake. (a) The GSN station distribution with respect to the epicenter. (b) Estimated relative seismic energy release with plus symbols showing spatial centroids at different times. (c) Estimated slip using a simple energy/moment scaling relationship. Aftershock locations and selected focal mechanisms are also plotted. The thick gray contour outlines our estimate of the fault plane.
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We image the rupture zone of the March 28, 2005, Sumatra Mw 8.7 earthquake by directly back-projecting teleseismic P waves to their source. We use broadband, vertical-component seismograms recorded by the Global Seismic Network and the Japanese Hi-net network. Our resulting images agree favorably with the aftershock distribution and the location of the Harvard centroid moment tensor. The back-projected energy suggests that the rupture was 120 s long and propagated at 2.9-3.3 km/s from the hypocenter in two directions delayed by about 50 s: first towards the northeast for about 100 km and then toward the southeast for about 200 km. The seismic radiation throughout the rupture zone is characterized by periods between 2-10 s. However, the southern half of the rupture zone generated additional longer-period energy between 10-30 s. The rupture occurred over a surface area of about 70,000 km2, which is fairly consistent with a Mw 8.7 event on a nearly horizontal fault plane. It appears that this earthquake is similar to the 1861 Mw 8.3-8.5 thrust event in its location, size, and geometry.


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