Rupture Process During the 2015 Illapel, Chile Earthquake: Zigzag-Along-Dip Rupture Episodes
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We constructed a seismic source model for the 2015 M W 8.3 Illapel, Chile earthquake, which was carried out with the kinematic waveform inversion method adopting a novel inversion formulation that takes into account the uncertainty in the Green’s function, together with the hybrid backprojection method enabling us to track the spatiotemporal distribution of high-frequency (0.3–2.0 Hz) sources at high resolution by using globally observed teleseismic P-waveforms. A maximum slip amounted to 10.4 m in the shallow part of the seismic source region centered 72 km northwest of the epicenter and generated a following tsunami inundated along the coast. In a gross sense, the rupture front propagated almost unilaterally to northward from the hypocenter at <2 km/s, however, in detail the spatiotemporal slip distribution also showed a complex rupture propagation pattern: two up-dip rupture propagation episodes, and a secondary rupture episode may have been triggered by the strong high-frequency radiation event at the down-dip edge of the seismic source region. High-frequency sources tends to be distributed at deeper parts of the slip area, a pattern also documented in other subduction zone megathrust earthquakes that may reflect the heterogeneous distribution of fracture energy or stress drop along the fault. The weak excitation of high-frequency radiation at the termination of rupture may represent the gradual deceleration of rupture velocity at the transition zone of frictional property or stress state between the megathrust rupture zone and the swarm area.
Keywords2015 Illapel Chile earthquake Source process Kinematic waveform inversion Hybrid backprojection Subduction zone earthquake Along-dip rupture propagation
Teleseismic waveforms and the strong motion data from the networks; Antarctic Seismographic Argentinean Italian Network (AI), Canadian National Seismograph Network (CN), GEOSCOPE (G), Global Telemetered Seismograph Network (USAF/USGS, GT), Global Seismograph Network (GSN - IRIS/IDA, II), Global Seismograph Network (GSN - IRIS/USGS, IU), and Red Sismologica Nacional (C1) are downloaded through the IRIS-DMC. Figures were generated with the Generic Mapping Tools (Wessel and Smith 1998). The authors thank Amato Kasahara and Bogdan Enescu for their valuable comments and suggestions. This work was supported by KAKENHI grant 24310133 from the Japan Society for the Promotion of Science. Chilean researchers would like to thank CONICYT grant FONDAP 15110017, FONDECYT 11140424 and the Chile-Japan Joint Project on Enhancement of Technology to Develop Tsunami Resilient Communities, sponsored by the Japan Science and Technology Agency (JST) and the Japan International Cooperation Agency through its SATREPS initiative. We acknowledge the editor and the two anonymous reviewers for their valuable comments and suggestions, which contribute to the significant improvement of the manuscript.
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