Earthquake supercycles on the Mentawai segment of the Sunda megathrust in the seventeenth century and earlier. Issue 1 (26th January 2017)

• Record Type: Journal Article
• Authors: Philibosian, Belle; Sieh, Kerry; Avouac, Jean‐Philippe; Natawidjaja, Danny H.; Chiang, Hong‐Wei; Wu, Chung‐Che; Shen, Chuan‐Chou; Daryono, Mudrik R.; Perfettini, Hugo; Suwargadi, Bambang W.; Lu, Yanbin; Wang, Xianfeng
• Is Part Of: Journal of geophysical research. Volume 122:Issue 1(2017)
• Page Start: 642
• Page End: 676
• Publication Date: 2017-01-26
• Subjects: earthquake cycle -- Sunda megathrust -- microatoll -- paleoseismology -- paleogeodesy -- Mentawai Islands; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1002/2016JB013560
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: 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. Plain Language Summary: The Sunda megathrust, a tectonic plate boundary fault which lies offshore west of Sumatra, has ruptured in many historical and recent earthquakes such as the magnitude 9.15 Aceh‐Andaman event in 2004. In order to anticipate the size and timing of earthquakes that are likely to be produced by this fault in the future, a record of past earthquakes is required. Coral skeletons hundreds of years old preserve evidence of past fault ruptures that uplifted the Mentawai Islands southwest of Sumatra. Our detailed analysis of corals that grew in the 17th century and earlier, combined with our past studies of corals from other time periods, reveals the breadth of variability as well as patterns that inform our expectations for future earthquake rupture. We present evidence that earthquakes typically occur in clusters separated by one to two centuries of quiescence, but each earthquake cluster evolves uniquely with different parts of the fault rupturing in various combinations and temporal sequences. Key Points: Five megathrust ruptures occurred below the Mentawai Islands during the seventeenth century, the culmination of an earthquake supercycle As was the case for the 1797/1833 culmination, the pattern of megathrust coupling changed during the rupture sequence Older coral data support our characterization of Mentawai segment megathrust behavior, informing future expectations