Aftershock Activity at Intermediate-Depth Earthquakes in Northern Chile Controlled by Plate Hydration
<p>We investigate the differences of the seismic source and aftershock activity using kinematic inversions and template matching respectively, for the six largest intraslab intermediate-depth earthquakes occurred in northern Chile (Mw ~6.3) since 2010 at depths between 90 and 130 km and recorded by dense strong-motion and broad-band seismic networks. In addition, we developed a thermal model using the finite element method&#160;in the study region with the aim of analyze the impact of temperature on seismic behavior as the oceanic plate subducts.&#160;Our results show that geometries of rupture zones are similar, with semi-axis for an elliptical patch approach about 5 km, and stress drop values between 7 and 30 MPa. On the other hand, the number of aftershocks exhibits clear differences, and their amount decreases with increasing the depth within the slab bounded by the 450 &#186;C isotherm, which represents a limit between a high-hydrated and a dry or low-hydrated region. Furthermore, mainshocks occur at distances from the top of the slab from 7 to 40 km, and all of them exhibit normal focal mechanisms suggesting that the extensional regimen deepens within the slab to the 700-750 &#186;C isotherm-depth. We suggest that in northern Chile the abrupt decrease of aftershocks in the lower part of the extensional regimen is caused by the absence of a hydrated slab at those depths.</p>