The Role of Stress Barriers on the Shape of Future Earthquakes in the Mentawai Section of the Sunda Megathrust

Abstract

The underlying causes of apparent barriers to rupture propagation on earthquake faults that appear strongly to constrain rupture shape and slip distributions, are the ongoing subject of research. Preseismic stress shadows on the rupturing segment, resulting from the history of slip preceding a great earthquake, are proposed here as one possible cause of such barriers. We focus on the Mentawai section of the Sunda megathrust since it is unique in having its long seismic history recorded in shallow water corals, as well as detailed slip distributions for events in the last seismic cycle, and modern geodetic information on the distribution of interseismic coupling. We show that stress shadows left by the moment magnitude (M) 8.7 1797 and M = 8.9 1833 earthquakes on the section persist up to today, and likely acted as barriers to the ruptures in 2007 (M = 8.4 and 7.9) and 2010 (M = 7.8), potentially resulting in much smaller earthquakes than would have occurred otherwise.