Earthquake supercycles on the Mentawai segment of the Sunda megathrust in the seventeenth century and earlier
Over at least the past millennium, the Mentawai segment of the Sunda megathrust has failed in sequences of closely timed events rather than in single end-to-end ruptures—each the culmination of an earthquake "supercycle." Here we synthesize the sixteenth- and seventeenth-century coral microatoll records into a chronology of interseismic and coseismic vertical deformation. We identify at least five discrete uplift events in about 1597, 1613, 1631, 1658, and 1703 that likely correspond to large megathrust ruptures. This sequence contrasts with the following supercycle culmination, which involved only two large ruptures in 1797 and 1833. Fault slip modeling suggests that together the five cascading ruptures involved failure of the entire Mentawai segment. Interseismic deformation rates also changed after the onset of the rupture sequence, as they did after the 1797 earthquake. We model this change as an altered distribution of fault coupling, presumably triggered by the ~1597 rupture. We also analyze the far less continuous microatoll record between A.D. 1 and 1500. While we cannot confidently delineate the extent of any megathrust rupture during that period, all evidence suggests that individual major ruptures involve only part of the Mentawai segment, often overlap below the central Mentawai Islands, often trigger coupling changes, and occur in clusters that cumulatively cover the entire Mentawai segment at the culmination of each supercycle. It is clear that each Mentawai rupture sequence evolves uniquely in terms of the order and grouping of asperities that rupture, suggesting heterogeneities in fault frictional properties at the ~100 km scale.
Additional Information© 2016 The Authors. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. Received 17 SEP 2016; Accepted 12 DEC 2016; Accepted article online 15 DEC 2016; Published online 26 JAN 2017. All data used in this paper are included in the main text or supporting information. This project was supported by National Science Foundation grants 0208508, 0530899, 0538333, and 0809223 to K.S.; by Sumatran Paleoseismology grant M58B50074.706022; by the National Research Foundation Singapore and the Singapore Ministry of Education under the Research Centres of Excellence initiative through the Earth Observatory of Singapore; by the Research Center for Geotechnology at the Indonesian Institute of Sciences (LIPI); by the Caltech Tectonics Observatory; and by the Gordon and Betty Moore Foundation. Also, the Japanese documentary agency NHK funded a special one-week final field expedition in 2012. U-Th dating was supported by the Taiwan ROC MOST and NTU grants 104-2119-M-002-003, 105-2119-M-002-001, and 105R7625 to C.-C. S. We thank Dudi Prayudi, Imam Suprihanto, John Galetzka, and all the crew members of the K.M. Andalas for field support, Ke (Coco) Lin for assistance with U-Th dating at the HISPEC Laboratory at the National Taiwan University, and Aron Meltzner, Emma Hill, and Lujia Feng for helpful discussions. This paper was improved thanks to thoughtful and thorough reviews by Rob Witter and an anonymous reviewer. This is Earth Observatory of Singapore contribution no. 137 and Caltech Tectonics Observatory contribution 216.
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