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Rapidly Estimated Seismic Source Parameters for the 16 September 2015 Illapel, Chile M w 8.3 Earthquake

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Abstract

On 16 September 2015, a great (M w 8.3) interplate thrust earthquake ruptured offshore Illapel, Chile, producing a 4.7-m local tsunami. The last major rupture in the region was a 1943 M S 7.9 event. Seismic methods for rapidly characterizing the source process, of value for tsunami warning, were applied. The source moment tensor could be obtained robustly by W-phase inversion both within minutes (Chilean researchers had a good solution using regional data within 5 min) and within an hour using broadband seismic data. Short-period teleseismic P wave back-projections indicate northward rupture expansion from the hypocenter at a modest rupture expansion velocity of 1.5–2.0 km/s. Finite-fault inversions of teleseismic P and SH waves using that range of rupture velocities and a range of dips from 16°, consistent with the local slab geometry and some moment tensor solutions, to 22°, consistent with long-period moment tensor inversions, indicate a 180- to 240-km bilateral along-strike rupture zone with larger slip northwest to north of the epicenter (with peak slip of 7–10 m). Using a shallower fault model dip shifts slip seaward toward the trench, while a steeper dip moves it closer to the coastline. Slip separates into two patches as assumed rupture velocity increases. In all cases, localized ~5 m slip extends down-dip below the coast north of the epicenter. The seismic moment estimates for the range of faulting parameters considered vary from 3.7 × 1021 Nm (dip 16°) to 2.7 × 1021 Nm (dip 22°), the static stress drop estimates range from 2.6 to 3.5 MPa, and the radiated seismic energy, up to 1 Hz, is about 2.2–3.15 × 1016 J.

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Acknowledgments

We thank Luis Rivera for his program for calculating stress drop for variable slip models, and Charles Ammon for sharing preliminary R1 source time functions and their azimuthal patterns. Sebastian Riquelme provided information on the regional W-phase inversion that helped guide the tsunami alert and evacuation. The IRIS DMS data center was used to access the seismic data from Global Seismic Network and Federation of Digital Seismic Network stations. We thank the editor and two anonymous reviewers for helpful comments on the manuscript. This work was supported by NSF grant EAR1245717 (T. L.).

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Authors and Affiliations

  1. Seismological Laboratory, California Institute of Technology, MS 252-21, Pasadena, CA, 91101, USA

    Lingling Ye & Hiroo Kanamori

  2. Department of Earth and Planetary Sciences, University of California Santa Cruz, Santa Cruz, CA, 95064, USA

    Thorne Lay

  3. Department of Geology and Geophysics, University of Utah, Salt Lake City, UT, 84112, USA

    Keith D. Koper

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  1. Lingling Ye
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Correspondence to Thorne Lay.

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This paper is part of the article collection on “Illapel, Chile, Earthquake on September 16th, 2015”.

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24_2015_1202_MOESM1_ESM.mpg

Supplementary material 1 (MPG 2139 kb) Movie S1: Animation of the back-projection of 0.5–2.0 Hz teleseismic P waves from North America to the source region of the 16 September 2015 Illapel earthquake. Each 0.5-s snapshot indicates the spatial distribution of relative power of the back-projected P wave energy with fourth-root stacking over the source grid. The time varying power in each time frame is shown at the top, with a red line indicating time relative to the origin

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Ye, L., Lay, T., Kanamori, H. et al. Rapidly Estimated Seismic Source Parameters for the 16 September 2015 Illapel, Chile M w 8.3 Earthquake. Pure Appl. Geophys. 173, 321–332 (2016). https://doi.org/10.1007/s00024-015-1202-y

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