Isolating along-strike variations in the depth extent of shallow creep and fault locking on the northern Great Sumatran Fault
The Great Sumatran Fault system in Indonesia is a major right-lateral trench-parallel system that can be divided into several segments, most of which have ruptured within the last century. This study focuses on the northern portion of the fault system which contains a 200-km-long segment that has not experienced a major earthquake in at least 170 years. In 2005, we established the Aceh GPS Network for the Sumatran Fault System (AGNeSS) across this segment. AGNeSS observes large displacements which include significant postseismic deformation from recent large megathrust earthquakes as well as interseismic deformation due to continued elastic loading of both the megathrust and the strike slip system. We parameterize the displacements due to afterslip on the megathrust using a model based on a rate- and state-dependent friction formalism. Using this approach, we are able to separate afterslip from other contributions. We remove predicted deformation due to afterslip from the observations, and use these corrected time series to infer the depth of shallow aseismic creep and deeper locked segments for the Great Sumatran Fault. In the northern portion of this fault segment, we infer aseismic creep down to 7.3 ± 4.8 km depth at a rate of 2.0 ± 0.6 cm/year. In the southwestern portion of the segment, we estimate a locking depth of 14.8 ± 3.4 km with a downdip slip rate of 1.6 ± 0.6 cm/year. This portion of the fault is capable of producing a magnitude 7.0 earthquake.
Additional Information© 2012 American Geophysical Union. Received 18 October 2011; revised 9 May 2012; accepted 14 May 2012; published 28 June 2012. We thank the Editor, Tom Parsons, and two reviewers, Danny Hilman Natawidjaja and an anonymous reviewer, for their thoughtful reviews and valuable comments that helped to improve the manuscript. This is Caltech Seismological Laboratory contribution number 10076 and Caltech Tectonics Observatory contribution number 197. This material is supported by the grants-in-aid for scientific research (19253003 and 23740337) of MEXT of Japan.
Published - Ito2012p18973J_Geophys_Res-Sol_Ea.pdf