3‐D active source tomography around Simeulue Island offshore Sumatra: Thick crustal zone responsible for earthquake segment boundary

Abstract

[1] We present a detailed 3-D P-wave velocity model obtained by first-arrival travel-time tomography with seismic refraction data in the segment boundary of the Sumatra subduction zone across Simeulue Island, and an image of the top of the subducted oceanic crust extracted from depth-migrated multi-channel seismic reflection profiles. We have picked P-wave first arrivals of the air-gun source seismic data recorded by local networks of ocean-bottom seismometers, and inverted the travel-times for a 3-D velocity model of the subduction zone. This velocity model shows an anomalous zone of intermediate velocities between those of oceanic crust and mantle that is associated with raised topography on the top of the oceanic crust. We interpret this feature as a thickened crustal zone in the subducting plate with compositional and topographic variations, providing a primary control on the upper plate structure and on the segmentation of the 2004 and 2005 earthquake ruptures. Citation: Tang, G.,

What 2‐D multichannel seismic and multibeam bathymetric data tell us about the North Sumatra wedge structure and coseismic response

“…Our proposed backstop geometry (Figure ) lies between 2°N and 5°N, based on our interpretation of the structure and morphology of this part of the accretionary prism, backstop models in subduction settings [ Byrne et al ., ; Gutscher et al ., ; Storti et al ., ], and velocity models [ Klingelhoefer et al ., ; Singh et al ., ; Tang et al ., ]. For the northern region of our study area (Figures and a), we use a velocity model published by Singh et al [] as a basis for our backstop interpretation.…”

“…Furthermore, landward of this tip, the roof of the backstop must be seaward dipping, because it deforms younger wedge sediments into the extended landward vergence zone that we observe toward the Sunda Trench [ Byrne and Hibbard , ]. Velocity models generated for this part of the margin [ Chauhan et al ., ; Klingelhoefer et al ., ; Singh et al ., ; Shulgin et al ., ; Tang et al ., ] confirm that this backstop must also be composed of material with a compressional wave velocity in the ~5.5–6.8 km/s range, signifying a composition that approximates either continental crust or older, lithified accreted sediments overlying such crust.…”

“…Farther southeast, Klingelhoefer et al [] (Figure ) proposed a backstop under the Simeulue Basin based on seismic velocity of 6.3 km/s at ~6 km depth, which defines the proposed backstop roof, while a 6.8 km/s region at ~21 km depth defines its base. Around Simeulue Island, Tang et al [] have also proposed a backstop defined by a roof velocity of 6 km/s at ~8 km depth under the Simeulue Basin, with a dip to ~17 km depth seaward of Simeulue Island.…”

Three-dimensional velocity structure of the outer fore arc of the Colombia-Ecuador subduction zone and implications for the 1958 megathrust earthquake rupture zone

“…Many active source seismic experiments have been conducted over convergent margins, but most of them are 2‐D seismic experiments which do not map the extension and the variability of geologic features along strike. Only a small number of 3‐D refraction experiments have been carried out along subduction zones, e.g., in Chile near Valparaiso [ Zelt et al ., ] or more recently along the Lesser Antilles fore arc [ Evain et al ., ] or on the Sumatra fore arc [ Tang et al ., ]. In this paper we present the results of a 3‐D refraction survey along the Ecuador‐Colombia convergent margin located over the rupture of the 1958 subduction earthquake and the boundary with the rupture of the 1979 earthquake, in order to produce a volumetric image of the seismic velocity structure of this part of the subduction zone.…”

Structure of the Central Sumatran Subduction Zone Revealed by Local Earthquake Travel Time Tomography Using Amphibious Data

“…Bathymetry 10 and topography from the SRTM plus database (Becker et al 2009). Oceanic fracture zones from Cande et al (1989) and Tang et al (2013). Rupture zones of the great 1797 and 1833 earthquakes 15 are based on uplift of coral micro-atolls (Natawidjaja et al 2006).…”