Seismicity Distribution Near a Subducting Seamount in the Central Ecuadorian Subduction Zone, Space‐Time Relation to a Slow‐Slip Event

A temporary onshore-offshore seismic network deployed during the 2-year period of the Observacion SISmologica en ECuador project provides a detailed and well-focused image of the seismicity for magnitudes as low as 2.1 at the Central Ecuadorian subduction zone. During this 2-year experiment, the shallow and locked subduction patch shows little evidence of background seismicity that instead occurred downdip of the coupled patch at 20-km depth. In this region, seismicity is possibly controlled by the crustal faults bounding the sedimentary basin of Manabi and the rheology of the upper plate. The dip angle of the interplate contact zone, defined by a smooth interpolation through the hypocenters of thrust events, is consistent with a progressive increase from 6 degrees to 25 degrees from the trench to 20-km depth. Offshore, a seismic swarm, concomitant with a slow-slip event rupturing the highly coupled subduction megathrust, highlights the reactivation of secondary active faults within the thickened crust of the subducting Carnegie Ridge at the leading edge of a large oceanic seamount.