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Structure of the central Sumatran subduction zone revealed by local earthquake travel-time tomography using an amphibious network

Structure of the central Sumatran subduction zone revealed by local earthquake travel-time tomography using an amphibious network
Structure of the central Sumatran subduction zone revealed by local earthquake travel-time tomography using an amphibious network

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 vpĝ•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 Combining double low line 8.7) and to the south in 2007 (Bengkulu earthquake, Mw Combining double low line 8.5). The 2-D and 3-D 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 3-D 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 ĝ1/4 180 km distance to the trench. vp velocities beneath the magmatic arc and the Sumatran fault zone (SFZ) are around 5 km sĝ'1 at 10 km depth and the vpĝ•vs ratios in the uppermost 10 km are low, indicating the presence of felsic lithologies typical for continental crust. We find moderately elevated vpĝ•vs values of 1.85 at ĝ1/4 150 km distance to the trench in the region of the Mentawai Fault. vpĝ•vs ratios suggest an 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 the Mentawai Islands and the Sumatra mainland possibly reflect a reduced thickness of the overriding crust.

1869-9510
1035-1049
Lange, Dietrich
2bd36fe1-e600-42f0-b150-197a8e14f5f2
Tilmann, Frederik
069b7049-5894-49e5-a2a3-bca816a3893b
Henstock, Tim
27c450a4-3e6b-41f8-97f9-4e0e181400bb
Rietbrock, Andreas
e4656f22-06be-40fe-8f98-7f88c351c434
Natawidjaja, Danny
a5bfe94e-28fc-4cfe-9115-56603838c343
Kopp, Heidrun
c33e910c-127a-437c-843a-139f4c4380d5
Lange, Dietrich
2bd36fe1-e600-42f0-b150-197a8e14f5f2
Tilmann, Frederik
069b7049-5894-49e5-a2a3-bca816a3893b
Henstock, Tim
27c450a4-3e6b-41f8-97f9-4e0e181400bb
Rietbrock, Andreas
e4656f22-06be-40fe-8f98-7f88c351c434
Natawidjaja, Danny
a5bfe94e-28fc-4cfe-9115-56603838c343
Kopp, Heidrun
c33e910c-127a-437c-843a-139f4c4380d5

Lange, Dietrich, Tilmann, Frederik, Henstock, Tim, Rietbrock, Andreas, Natawidjaja, Danny and Kopp, Heidrun (2018) Structure of the central Sumatran subduction zone revealed by local earthquake travel-time tomography using an amphibious network. Solid Earth, 9 (4), 1035-1049. (doi:10.5194/se-9-1035-2018).

Record type: Article

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 vpĝ•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 Combining double low line 8.7) and to the south in 2007 (Bengkulu earthquake, Mw Combining double low line 8.5). The 2-D and 3-D 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 3-D 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 ĝ1/4 180 km distance to the trench. vp velocities beneath the magmatic arc and the Sumatran fault zone (SFZ) are around 5 km sĝ'1 at 10 km depth and the vpĝ•vs ratios in the uppermost 10 km are low, indicating the presence of felsic lithologies typical for continental crust. We find moderately elevated vpĝ•vs values of 1.85 at ĝ1/4 150 km distance to the trench in the region of the Mentawai Fault. vpĝ•vs ratios suggest an 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 the Mentawai Islands and the Sumatra mainland possibly reflect a reduced thickness of the overriding crust.

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Accepted/In Press date: 31 July 2018
e-pub ahead of print date: 21 August 2018

Identifiers

Local EPrints ID: 424389
URI: http://eprints.soton.ac.uk/id/eprint/424389
ISSN: 1869-9510
PURE UUID: 7817c550-eec6-4099-a6c1-898a4b7bafac
ORCID for Tim Henstock: ORCID iD orcid.org/0000-0002-2132-2514

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Date deposited: 05 Oct 2018 11:36
Last modified: 07 Oct 2020 01:44

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