Revisiting the 2015 Mw=8.3 Illapel Earthquake. From Kinematic Rupture Inversion to Rupture Dynamics.

The 2015 Mw=8.3 Illapel earthquake is one of the largest mega-thrust earthquakes that have been recorded in the Chilean subduction zone. Previous studies indicate a rupture propagation from the hypocenter to shallower parts of the fault, with a maximum slip varying from 10 to 16 meters. The amount of shallow slip differs dramatically between rupture models with some results showing almost no slip at the trench and other models with significant slip at shallow depth. In this work, we revisit this event by combining a comprehensive dataset including continuous and survey GPS corrected for post-seismic and aftershock signals, ascending and descending InSAR images of the Sentinel-1A satellite, tsunami data along with high-rate GPS and doubly integrated strong-motion waveforms. We follow a Bayesian approach, in which we obtain an ensemble of models, and not a unique solution. The kinematic inversion is done using the cascading capability of the AlTar algorithm, allowing us to first get a static solution before integrating waveform data in a joint model. This approach relies on an error model incorporating measurement and prediction uncertainties. To account for modeling uncertainties of waveform data, we explore the possibility to compute prediction error covariance using a 2nd order perturbation approach. Preliminary kinematic models show a rupture with two main slip patches. Rupture times suggest that an encircling rupture is occurring in the vicinity of the deeper slip asperity as suggested by previous back projection results. To gain insight into rupture dynamics, we use kinematic models to compute the stress evolution on the fault as a function of time. We compute the breakdown work density from the stress evolution and compare the resulting probability density estimates with similar calculations done for other earthquakes.