A combined geodetic and seismic model for the Mw 8.3 2015 Illapel (Chile) earthquake

The 2015 September 16 Mw 8.3 Illapel earthquake occurred on the subduction megathrust offshore of the Chilean coastline between the towns of Valparaiso and Coquimbo. This earthquake is the 3rdevent with Mw>8 to impact coastal Chile in the last 6 years. It occurred north of both the 2010 Mw 8.8 Maule earthquake and the 1985 Mw 8.0 Valparaiso earthquake. While the location of the 2015 earthquake is close to the inferred location of a large earthquake in 1943, comparison of seismograms from the two earthquakes suggests the recent event is not clearly a repeat of the 1943 event. To gain a better understanding of the distribution of coseismic fault slip, we develop a finite fault model that is constrained by a combination of static GPS offsets, Sentinel 1a ascending and descending radar interferograms, tsunami waveform measurements made at selected DART buoys, high rate (1 sample/sec) GPS waveforms and strong motion seismic data. Our modeling approach follows a Bayesian formulation devoid of a priori smoothing thereby allowing us to maximize spatial resolution of the inferred family of models. The adopted approach also attempts to account for major sources of uncertainty in the assumed forward models. At the inherent resolution of the model, the posterior ensemble of purely static models (without using high rate GPS and strong motion data) is characterized by a distribution of slip that reaches as much as 10 m in localized regions, with significant slip apparently reaching the trench or at least very close to the trench. Based on our W-phase point-source estimate, the event duration is approximately 1.7 minutes. We also present a joint kinematic model and describe the relationship of the coseismic model to the spatial distribution of aftershocks and post-seismic slip.