Kinematic and spontaneous rupture models of the 2005 Tarapacá intermediate depth earthquake

SUMMARY The 2005 June 13, an intraplate, intermediate depth earthquake (M w = 7.8, 98 km depth) occurred in northern Chile. Previous studies show that this earthquake is a slab-pull event with down dip extensional source mechanism. However, the physical origin and the role in seismic cycle of this kind of event are still under debate. We present a seismological source study from strong motion data, based on the simplified slip patch kinematic parametrization. We find two distinct sources. The main source is almost centred around the hypocentre and triggers the secondary one, situated deeper in the slab. The weaknesses and uncertainties of the kinematic models are partly resolved and discussed by constructing dynamic spontaneous rupture models with two radiative asperities and one embedding zone of non-radiative slip process, a required feature to fulfil the seismic moment constraint. Two kinds of models are compatible with observations: a crack mode model (combined with fast rupture velocity and small zone of non-radiative slip) and a pulse mode model (combined with slower rupture velocity and large zone of non-radiative slip). The fast rupture model is preferred for its physical simplicity. Replacing our result in the geometry and thermal contexts of the subduction, we conclude that the rupture has probably broken the whole lithosphere by encountering little resistance and without being very sensitive to the presence of the double seismic zone. This suggests that the rupture happens along a weak plane, on which large slab instabilities can take place.