The Mw=8.1 Pisagua Earthquake of 1 April 2014

On 1 April 2014, the Pisagua earthquake ruptured the northern portion of the north Chilean seismic gap that remained devoid of large seismic events in the previous 137 years. The W-phase inversion yields an almost purely double-couple solution consistent with Global CMT and the local slab geometry. This event was preceded by two weeks of intense foreshock activity and followed by a large Mw=7.7 aftershock. In this study, we estimate the detailed rupture process of the mainshock using ALTAR: an innovative Bayesian sampler that is now implemented to run on GPU and allows sampling of posterior PDFs for high-dimensional problems. Our observations include InSAR, high-rate GPS and Tsunami data. We include a full data covariance matrix to account for measurement uncertainties and prediction error. This covariance model enables a physical basis for the relative weighting between available datasets and provides more realistic estimates of uncertainty on the inferred parameters. Our results indicate a compact slip zone located down dip of the hypocenter. The absence of shallow rupture is mainly controlled by tsunami observations. In the same way, the 1995 Antofagasta and the 2001 Arequipa earthquakes did not involve any slip near the trench. Using land-based geodetic data, it is fundamentally difficult to know if shallow portions of the north Chilean subduction zone are seismogenic or not. Therefore, as for the 2011 Tohoku event, we cannot exclude the occurrence of a major event rupturing the southern portion of the seismic gap and driving slip at shallow depth.