Seismic structure and tectonics of the continental wedge overlying the source region of the Iquique Mw8.1 2014 earthquake

Abstract

On April 1, 2014, a large earthquake (Mw = 8.1) ruptured the central part of a historic seismic gap in northern Chile. In order to study the relationship between the co-seismic rupture characteristics and the crustal structure of the subduction zone, we processed a trench-perpendicular seismic reflection profile acquired across the zone of maximum slip and generated a P-wave velocity model. The results show a frontal prism in the continental wedge characterized by low velocities that increase rapidly towards the shore and acted as a barrier for trenchward propagation of aftershocks. Landward, a transition zone with increasing upper crust velocity (4-5 km/s) concentrates most of the aftershocks. In addition, a trench-ward dipping set of fault zones is observed along the continental wedge associated to the Iquique forearc basin formation (1.5 km thick at the depocenter on this profile). We identify three stratigraphic units within the basin. A landward tilt and thickness increase is detected in each stratigraphic unit, along with growth strata and domino structures, suggesting landward migration of syn-extensional deformation in response to basal subduction erosion. By extrapolating our results to the plate boundary and based on published focal mechanisms of intra-crustal seismicity, we find a strong spatial correlation between the Iquique basin and the highest slip area for the 2014 earthquake, suggesting long-term extensional deformation due to coseismic tensional stresses.