Similarities in the rupture process and cascading asperities between neighboring fault patches and seismic implications: The 2002–2009 Sumbawa (Indonesia) earthquakes with moment magnitudes of 6.2–6.6

Abstract

The Flores Thrust is a southward-dipping, low-to-moderate angle submarine active fault in the eastern Sunda-Banda back-arc (Indonesia). Significant shallow-depth destructive earthquakes have been reported along this fault zone. From 2002 to 2009, one of its fault segments, called the Sumbawa segment, experienced five earthquakes with moment magnitude (MW) values of 6.2–6.6. In this study, we performed finite-fault rupture inversions for these earthquakes, constrained with teleseismic body and surface waveforms, to investigate the characteristics of earthquake ruptures along this fault zone. We obtained the source-time-functions and finite-fault rupture models for these five earthquakes. Results indicated that ruptures often propagated along-strike or down-dip. The ruptures were initiated from the middle crust (depth of approximately 12–17 km) and exhibited a comparable initiation behavior to their entire rupture. The rupture speeds and stress drops were approximately 2.0–2.5 km/s and 1.0–2.0 MPa, respectively. Five cascading asperities ruptured neighboring fault patches and did not overlap each other. The characteristics of earthquake source parameters and rupture processes obtained in this study are robust and helpful for future regional seismic hazard assessment and earthquake early warning studies. These cascading asperities might be related to the fault immaturity of the western Flores Thrust. Alternatively, these earthquakes may act as asperities located at the down-dip patches of the Sumbawa segment, and its shallower section still has a potential of ruptures with MW > 7.0.