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Solid Earth An interactive open-access journal of the European Geosciences Union

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© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
04 Jan 2018
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Solid Earth (SE).
Structure of the Central Sumatran Subduction Zone Revealed by Local Earthquake Travel Time Tomography Using Amphibious Data
Dietrich Lange1, Frederik Tilmann2,6, Tim Henstock3, Andreas Rietbrock4, Danny Natawidjaja5, and Heidrun Kopp1,7 1GEOMAR Helmh oltz Centre for Ocean Research Kiel, Germany
2Helmholtz-Zentrum Potsdam, Deutsches GeoForschungsZentrum GFZ, Germany
3University of Southampton, United Kingdom
4University of Liverpool, Liverpool, UK
5LabEarth, Indonesian Institute of Sciences (LIPI)
6Freie Universität Berlin, Berlin, Germany
7Christian-Albrechts-Universität zu Kiel, Germany
Abstract. The Sumatran subduction zone exhibits strong seismic and tsunamogenic potential with the prominent examples of the 2004, 2005 and 2007 earthquakes. Here, we invert travel time data of local earthquakes for vp and vp/vs velocity models of the central Sumatran forearc. Data were acquired by an amphibious seismometer network consisting of 52 land stations and 10 ocean bottom seismometers located on a segment of the Sumatran subduction zone that had not ruptured in a great earthquake since 1797 but witnessed recent ruptures to the north in 2005 (Nias earthquake, Mw = 8.7) and to the south in 2007 (Bengkulu earthquake, Mw = 8.5). 2D and 3D vp velocity anomalies reveal the downgoing slab and the sedimentary basins. Although the seismicity pattern in the study area appears to be strongly influenced by the obliquely subducting Investigator Fracture Zone to at least 200 km depth, the 3D velocity model shows prevailing trench parallel structures at depths of the plate interface. The tomographic model suggests a thinned crust below the basin east of the forearc islands (Nias, Pulau Batu, Siberut) at ~ 180 km distance to the trench. Vp velocities beneath the magmatic arc and the Sumatran fault zone SFZ are around 5 km/s at 10 km depth and the vp/vs ratios in the uppermost 10 km are low, indicating the presence of felsic lithologies typical for continental crust. We find moderately elevated vp/vs values of 1.85 at ~ 150 km distance to the trench in the region of the Mentawai fault. Vp/vs ratios suggest absence of large scale alteration of the mantle wedge and might explain why the seismogenic plate interface (observed as a locked zone from geodetic data) extends below the continental forearc Moho in Sumatra. Reduced vp velocities beneath the forearc basin covering the region between Mentawai Islands and the Sumatra mainland possibly reflect a reduced thickness of the overriding crust.

Citation: Lange, D., Tilmann, F., Henstock, T., Rietbrock, A., Natawidjaja, D., and Kopp, H.: Structure of the Central Sumatran Subduction Zone Revealed by Local Earthquake Travel Time Tomography Using Amphibious Data, Solid Earth Discuss.,, in review, 2018.
Dietrich Lange et al.
Dietrich Lange et al.
Dietrich Lange et al.


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