The 2018 Mw7.5 Palu earthquake, a gradually accelerating super-shear rupture stopped by stress shadows in a complex fault system
Abstract
What controls the initiation, propagation and termination of an earthquake rupture? Answers to this fundamental question are critical to better understanding earthquake physics and preparing for future seismic events. Here we combine seismological, geodetic and geological observations, as well as written records to address this question for the 2018 Mw7.5 Palu earthquake.
Epicenters relocated using regional seismic data show that the mainshock, probably triggered by a Mw6.1 foreshock, started on a less active, near-vertical strike-slip fault. The rupture then propagated unilaterally towards the south through at least two transpressional step-overs, along a distance of 50 km, before it reached the more active Palu-Koro fault (slip rate nearly 5 cm/yr). As revealed by SAR/InSAR images, back-projection, multiple point source and finite fault inversions, the first 50 km of the rupture did not reach to the surface, and the rupture speed increased gradually from 2.4 to 3.3 km/s. There is no clear geomorphological signature of a strike-slip fault for this part of the rupture. Once the rupture reached the east-dipping Palu-Koro fault, the rupture accelerated to 4.1 km/s (super-shear). The slip extended from the surface to 12 km depth, along a 50-km long fault segment, with nearly 8 m of surface offset at the city of Palu. The geomorphological signature of this fault segment is clear. The smooth geometry and mature nature of this fault segment probably allowed the rupture to accelerated to super-shear. The rupture then overcame a 5-km transtensional step-over and continued on a west-dipping fault segment for 20 km before it stopped. As inferred from written historical records, the southern fault segment likely slipped during the Ms 6.3 earthquake in 1907, while a fault segment further to the south produced a Ms 7.3 event in 1909, through a length of more than 40 km. These events likely created a stress shadow that could have played a role in stopping the 2018 event. The 2018 event has likely loaded these faults segments to the south, increasing their seismic hazard. This event provides insight into the complex interactions of earthquake dynamics and fault structure. Dynamic rupture simulations aimed at forecasting future events must consider these complexities.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMNH23F3550W
- Keywords:
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- 4313 Extreme events;
- NATURAL HAZARDSDE: 4315 Monitoring;
- forecasting;
- prediction;
- NATURAL HAZARDSDE: 4341 Early warning systems;
- NATURAL HAZARDSDE: 4564 Tsunamis and storm surges;
- OCEANOGRAPHY: PHYSICAL