The 2007 Mentawai earthquake sequence on the Sumatra megathrust
Abstract
The Sumatra Megathrust has recently produced a flurry of large interplate earthquakes starting with the giant Mw 9.15, Aceh earthquake of 2004. All of these earthquakes occurred within the area monitored by the Sumatra Geodetic Array (SuGAr), which provided exceptional records of near-field co-seismic and postseismic ground displacements. The most recent of these major earthquakes, an Mw 8.4 earthquake and an Mw 7.9 earthquake twelve hours later, occurred in the Mentawai islands area where devastating historical earthquakes had happened in 1797 and 1833. The 2007 earthquake sequence provides an exceptional opportunity to understand the variability of the earthquakes along megathrusts and their relation to interseismic coupling. The InSAR, GPS and teleseismic modeling shows that 2007 earthquakes ruptured a fraction of the strongly coupled Mentawai patch of the megathrust, which is also only a fraction of the 1833 rupture area. It also released a much smaller moment than the one released in 1833, or than the deficit of moment that has accumulated since. Both earthquakes of 2007 consist of 2 sub-events which are 50 to 100 km apart from each other. On the other hand, the northernmost slip patch of 8.4 and southern slip patch of 7.9 earthquakes abut each other, but they ruptured 12 hours apart. Sunda megathrust earthquakes of recent years include a rupture of a strongly coupled patch that closely mimics a prior rupture of that patch and which is well correlated with the interseismic coupling pattern (Nias-Simeulue section), as well as a rupture sequence of a strongly coupled patch that differs substantially in the details from its most recent predecessors (Mentawai section). We conclude that (1) seismic asperities are probably persistent features which arise form heterogeneous strain build up in the interseismic period; and (2) the same portion of a megathrust can rupture in different ways depending on whether asperities break as isolated events or cooperate to produce a larger rupture. The stress distribution on the portion of the Sunda megathrust that had ruptured in 1833 and 1797 was probably not adequate for the development of a single major earthquake of the coupled zone in 2007. Since the moment released in 2007 amounts to only a fraction of the deficit of moment that had accumulated as a result of interseismic strain since 1833, the potential for a large megathrust event in the Mentawai area remains large.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.T52B..03K
- Keywords:
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- 7215 Earthquake source observations (1240);
- 7230 Seismicity and tectonics (1207;
- 1217;
- 1240;
- 1242);
- 8170 Subduction zone processes (1031;
- 3060;
- 3613;
- 8413)