Slip Modes Along a Structurally-Driven Earthquake Barrier in Chile

Oceanic ridges often collocate with seismic barriers and episodic aseismic slip. However, how subducted seafloor topography drives interactions between slow and fast slip remains unclear. Here, using GNSS, InSAR and seismicity, we show interactions between a deep slow slip event (SSE) and a nearby shallow earthquake sequence that occurred in 2020 in northern Chile. These events overlap with the subducted Copiapo ridge, which has served as a barrier for historical earthquake ruptures. Gravity field data and seismic tomography reveal that the SSE nucleated in a region hosting a subducted seamount. Six months later, the seismic sequence dynamically triggered the acceleration and migration of the deep SSE, while afterslip and aftershocks propagated up to another subducted seamount at shallower depth. Our findings suggest that subducted seamounts influence fault hydromechanics, where high pore-pressure and rate strengthening material promote continuous slip release, reducing slip deficit. This process is modulated by SSEs and low magnitude seismic sequences.