Fault geometry and rupture patterns of the 2018 Lombok earthquakes - complex thrust faulting in a volcanic back-arc setting
Abstract
A series of destructive earthquakes occurred near Lombok, Indonesia in August 2018, beginning with a Mw 6.4 earthquake and followed by two Mw 6.9 events. Lombok is a volcanic island on the Sunda arc system - the earthquakes are unique examples of tectonically-driven thrust faulting next to an active volcano. Focal mechanisms of major events in the sequence indicate an east-west striking fault, consistent with the Flores thrust further to the west. The earthquakes pose several questions including how a major tectonic fault system interacts with an active volcano.
We address these questions with a comprehensive seismic analysis of the earthquake sequence including moment tensors from modelling of local and regional waveforms; centroid depths from modelling teleseismic waveforms; microseismicity obtained by a temporary nodal and broadband array deployment. Our results show that the major earthquakes have a strike parallel to the northern coast of the island. Earthquake depths increase gradually from ~10km in the west to ~18km in the east. The rupture process of the first Mw 6.9 earthquake, which has a rupture directivity to the west, is rougher than the second, deeper Mw 6.9 event, that ruptured towards the east, suggesting different frictional properties on these fault planes. The thermal and potentially fluid effects associated with the volcano's magma chamber are likely to play an important role in modulating the rupture smoothness and down dip extend of the events. Shallower faults were also activated in the aftershock sequences, indicating a complicated fault system in the region.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.S51E0440W
- Keywords:
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- 7209 Earthquake dynamics;
- SEISMOLOGY;
- 7215 Earthquake source observations;
- SEISMOLOGY;
- 7230 Seismicity and tectonics;
- SEISMOLOGY;
- 7290 Computational seismology;
- SEISMOLOGY