Characterizing the Variability of Supercycles on the Mentawai Segment of the Sunda Megathrust and Implications for Global Fault Behavior

Thursday, 18 December 2014: 4:00 PM
Kerry Sieh1, Belle Philibosian2, Jean-Philippe Avouac3, Danny Hilman Natawidjaja4, Hong-Wei Chiang1, Chung-Che WU5, Hugo Perfettini6, Chuan-Chou Shen7, Mudrik Rahmawan Daryono8 and Bambang Widoyoko Suwargadi4, (1)Nanyang Technological University, Singapore, Singapore, (2)Institut de Physique du Globe de Paris, Paris, France, (3)California Institute of Technology, Pasadena, CA, United States, (4)Research Center for Geotechnology, Indonesian Institute of Sciences, Bandung, Indonesia, (5)National Taiwan University, Taipei City, Taiwan, (6)ISTerre Institute of Earth Sciences, Saint Martin d'Hères, France, (7)NTU National Taiwan University, Taipei, Taiwan, (8)Indonesian Institute of Sciences (LIPI), Bandung, Indonesia
One of the key lessons of the last decade of great earthquakes is that long paleoseismic records are a vital part of the body of knowledge required for accurate earthquake forecasting, and that the longest, most detailed records provide the best understanding of the complete range of fault behavior. In addition to being the source of one of the decade’s great earthquakes, the Mentawai segment of the Sunda megathrust also has one of the most detailed paleoseismic and paleogeodetic records, thanks to studies of coral microatolls. The high spatial and temporal resolution of these records has illuminated many features that are difficult to discern using most other techniques. Examples of varying types of segmentation, asperity mosaicking, superimposed seismic cycles with varying periods, and time-varying interseismic coupling are all exhibited by this megathrust segment. While the northern end of the segment in the Batu Islands appears to be a persistent barrier to rupture throughout the paleoseismic record, the behavior of the central Mentawai segment is more heterogeneous. Ruptures from both ends generally terminate in this region, yet also often overlap by 100–200 km. This behavior, likely due to smaller-scale heterogeneities in frictional properties of the fault interface, results in the characteristic rupture of the Mentawai segment in a series of events rather than a single end-to-end rupture. Beyond that similarity, it is clear that each of these rupture sequences evolves uniquely in terms of the order and grouping of asperities that rupture. Additionally, the ruptures that begin the sequences frequently alter the distribution of fault coupling, thus influencing the progression of future ruptures. Heterogeneities in fault frictional properties at the scale seen in the Mentawai case are probably common and control the rupture extent, magnitude and distribution of slip in great earthquakes worldwide. Though the details are usually less clear, analogs to the Mentawai supercycles can be found in both subduction and continental faulting environments. The Mentawai example highlights many of the complexities researchers should expect to discover in seismic cycles on major faults around the world.