Structural evolution of backthrusting in the Mentawai Fault Zone, offshore Sumatran forearc

Abstract

[1] We present the interpretation of newly acquired high-quality industry-standard deep seismic reflection and swath bathymetry data to provide insight into the structural style and evolution of the Mentawai Fault Zone (MFZ). The MFZ lies along the boundary between the accretionary wedge and the proposed continental backstop. This zone exhibits arcuate ridges on the seafloor, convex toward the east. Beneath these ridges the structures developed as landward-vergent imbricated backthrusts in the inner part of the accretionary wedge and higher-angle backthrusts that deformed the forearc basin sediments. In the forearc high, anticlines were developed due to the seaward-vergent forearc high thrusts originating in the accretionary wedge. The imbricated backthrusts may have initiated during the Early-Middle Miocene contemporaneously with the slide and back-rotation of forearc high thrusts. In the Late Miocene, the higher-angle backthrusts were initiated. Continuous contraction induced the frontal higher-angle backthrusts and formed a fold-thrust belt toward the east during the Pliocene. The folds and thrusts were disturbed by diapirs and mud volcanoes. Backthrusting and fold-thrust belts developed in the MFZ may explain the compressional features observed at the boundary between the accretionary wedge and continental backstop along the southern Sumatra margin. The backthrusts along the MFZ are waning in activity and hence the risk of a large earthquake and associated tsunami at the present time should be small.

Deformasi Kompleks Di Pulau Simeulue, Sumatra: Interaksi Antara Struktur Dan Diapirisme

“…Di sepanjang busur muka Sumatera terdapat Zona Sesar Mentawai (MFZ) yang terpetakan dimulai dari sekitar Kepulauan Mentawai hingga di ujung selatan Busur Muka Sumatera (Mukti et al, 2012;Diament et al, 1992). Zona sesar ini terbentuk di antara pulau-pulau prisma akresi dengan cekungan busur muka.…”

“…Sepanjang busur Sumatra, salah satu struktur geologi yang unik adalah ditemukannya bukti adanya sesar anjak balik (backthrust) di daerah prisma akresi (Mukti et al, 2012). Apabila struktur sesar anjak balik ini dicermati pada penampang seismiknya, akan tampak bahwa sesar anjak balik pada segmen yang telah mengalami gempa besar akan menunjukkan adanya penguatan sinyal seismiknya (Singh et al, 2011b).…”

“…Data seismik juga menunjukkan bahwa sesar anjak balik ini menerus hingga ke dasar samudera (Singh et al, 2011a). Pada bagian selatan cekungan muka busur Sumatra di Kepulauan Mentawai, diketahui bahwa sesar anjak balik ini berkaitan dengan adanya kubah lumpur (mud diapir) (Mukti et al, 2012).…”

“…Bidang sesar dengan dip berarah palung juga teridentifikasi pada satu bidang sesar di bagian utara pulau dengan nilai N330 0 E / 20 0 dengan pitch 20 0 S. Bidang sesar ini mengganggu endapan sedimen lempung di atasnya, sehingga mungkin saja lokasi ini merupakan manifestasi kubah lumpur (Gambar 9C). Contoh kasus pada bagian selatan cekungan mukabusur Sumatra mengungkapkan bahwa kubah lumpur ini berkaitan dengan sesar anjak balik (Mukti et al, 2012) …”

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

“…Structural information is 45 known from active seismic reflection and refraction studies for a significant number of profiles (e.g. Franke et al, 2008;Dean et al, 2010;Klingelhoefer et al 2010, Mukti et al, 2012, Shulgin et al 2013. The Mentawai fault (Diament et al, Solid Earth Discuss., https://doi.org /10.5194/se-2017-128 Manuscript under review for journal Solid Earth Discussion started: 4 January 2018 c Author(s) 2018.…”