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The Sumatra Fault and Krakatau: How Regional Extension Shapes Volcanism in the Sunda Strait

Elisa Klein 1, Christian Berndt1, Jens Karstens1, Julie Christin Schindlbeck-Belo1, Jonas Preine2, Michel Kühn3, David Tappin4, Husrin Sameidi5, Sri Ardhyastuti5, Adam Budi Nugroho5, Shofia Karima5, Aditya Pratama5, Morelia Urlaub1

  • Affiliations: 1 RD4, GEOMAR Helmholtz Center for Ocean Research, Kiel, Germany; 2 Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole MA 02543, USA; 3 Lamont‐Doherty Earth Observatory, Columbia University, Palisades (NY), USA; 4 British Geological Survey, UK; 5 BRIN - National Research and Innovation Agency, Indonesia;

  • Presentation type: Poster

  • Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 164

  • Programme No: 2.2.28

  • Theme 2 > Session 2

Abstract

The contrasting subduction dynamics along the Indonesian subduction arc---perpendicular beneath Java and oblique beneath Sumatra---have resulted in the formation of a NW-moving sliver plate offshore Sumatra. The strike-slip motion ceases as the Sumatra Fault bends southward in the Sunda Strait, which hosts the highly active Krakatau volcano, leading to extension and the formation of the Semangko pull-apart basin. Krakatau, which was destroyed by a violent eruption in 1883, and its successor Anak Krakatau are prone to flank instability and are more southerly than volcanoes on Sumatra or Java. While both observations have been attributed to the regional extensional regime in the Sunda Strait having a significant influence on the evolution of Krakatau, the distribution of fault systems around and beneath Krakatau has remained poorly constrained. We integrate high-resolution 2D multichannel seismic data from the 2023 research cruise SO299-2 with an extensive high-resolution sparker seismic dataset acquired around the Krakatau Archipelago in 2018 and 2023 (UKGrant_Ref:NE/S003509/1) to investigate the tectonic controls on volcanism in this region. Our analysis identifies predominantly NW-SW to NNW-SSE striking normal faults, associated with the regional extension in the Sunda Strait. We interpret a major NW-SE striking, SW-dipping normal fault in the northwest of the study area as the north-eastern extension of the Sumatra Fault, which bends southward to form the eastern boundary fault of the Krakatau Graben, a mostly filled graben adjacent to the Semangko pull-apart basin. Krakatau lies on the flank of the horst which probably contributes to its instability and eruptive behaviour.