Limits of the seismogenic zone in the epicentral region of the 26 December 2004 great Sumatra‐Andaman earthquake: Results from seismic refraction and wide‐angle reflection surveys and thermal modeling

Abstract

[1] The 26 December 2004 Sumatra earthquake (M w = 9.1) initiated around 30 km depth and ruptured 1300 km of the Indo-Australian -Sunda plate boundary. During the Sumatra-OBS (ocean bottom seismometer) 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 the SeaCause II cruise, the deep structure of the source region of the great earthquake is revealed. Four to five kilometers 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 fore-arc basin. A high-velocity zone at the lower landward limit of the ray-covered domain, at 22 km 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 fore arc 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 fore-arc Moho. The deeper part of the rupture occurred along the contact between the mantle wedge and the downgoing plate.

The thermal structure of the subduction thrust within accretionary and erosive margins

“…This correlation is generally understood in terms of a change in frictional properties along the fault, either the brittle-ductile transition or the intersection of the subduction thrust with hydrated mantle (Hyndman et al, 1997;Peacock and Hyndman, 1999). However earthquakes that extend below the shallow mantle wedge at Sumatra, northeastern Japan, and the Mariana trench are leading to challenges of this view (Dessa et al, 2009;Emry et al, 2011;Heuret et al, 2011;Hino et al, 2000;Klingelhoefer et al, 2010;Simoes et al, 2004). The updip extent of observed seismicity appears well correlated with temperatures along the subduction thrust between 100°and 150°C (Hyndman andWang, 1993, 1995;Hyndman et al, 1997;Oleskevich et al, 1999).…”

Tsunami Wave Analysis and Possibility of Splay Fault Rupture During the 2004 Indian Ocean Earthquake

“…6a, the observation of surface deformation in this area is strong evidence in support of the notion that there was localized coseismic deformation in the area of the proposed splay fault during the 2004 earthquake. KLINGELHOEFER et al (2010) observed many landward and seaward vergent faults in the accretionary prism to the northwest of Salaut Besar. One of these landward vergent structures roughly correlates with the observed surface deformation and may indicate the presence of a family of such faults in the area (MELTZNER et al, 2010).…”

Bathymetry of the Indonesian Sunda margin-relating morphological features of the upper plate slopes to the location and extent of the seismogenic zone

“…Several studies were conducted in the area north of Simeulue island at 3 • N to 4 • N using MCS and wide-angle seismic studies Dessa et al, 2009;Klingelhoefer et al, 2010) as well as gravity and thermal modelling (Klingelhoefer et al, 2010). All of them obtain similar depths for the updip limit of the SZ in that region.…”