The limits of the seismogenic zone in the epicentral region of the 26 Dec. 2004 Great Sumatra Andaman earthquake: results from a seismic refraction and wideangle reflection surveys and thermal modeling
Abstract
The 26th December 2004 Sumatra earthquake (Mw=9.1) initiated around 30 km depth and ruptured 1300 km of the IndoAustralian/Sunda plate boundary. During the Sumatra-OBS survey a wide angle seismic profile was acquired across the epicentral region. A seismic velocity model was obtained from combined travel time tomography and forward modeling. Together with reflection seismic data from BGR's SeaCause II cruise, the deep structure of the source region of the great earthquake is revealed. Four to five km of sediments overlie the oceanic crust at the trench and the subducting slab can be imaged down to a depth of 35 km. We find a crystalline backstop 120 km from the trench axis, below the forearc basin. A high velocity zone, of mantle velocity at the lower landward limit of the ray-covered domain, at 22km depth, marks a shallow continental Moho, 170 km from the trench. The deep structure obtained from the seismic data was used to construct a thermal model of the forearc in order to predict the limits of the seismogenic zone along the plate boundary fault. Assuming 100-150°C as its updip limit, the seismogenic zone is predicted to begin 5-30 km from the trench. The downdip limit of the 2004 rupture as inferred from aftershocks is within the 350-450°C temperature range, but this limit is 210-250 km from the trench axis and is much deeper than the forearc Moho. The deeper part of the rupture occurred along the contact between the mantle wedge and downgoing plate. It is shown that it actually initiated along this deep mantle part of the thrust that is normally predicted to be aseismic by current models describing the seismogenesis in subduction zones.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.T23B1922D
- Keywords:
-
- 3025 MARINE GEOLOGY AND GEOPHYSICS / Marine seismics;
- 3060 MARINE GEOLOGY AND GEOPHYSICS / Subduction zone processes;
- 7230 SEISMOLOGY / Seismicity and tectonics;
- 7240 SEISMOLOGY / Subduction zones