Intraslab seismicity migration simultaneously with an interface slow slip event along the Ecuadorian subduction zone

Slow slip events (SSEs) are transient slip episodes taking place along the plate interface of subduction zones. They usually occur synchronously to tectonic tremors and/or seismic swarms, but the relationship between slip and seismicity remains unclear. Here, we study a well-instrumented seismic swarm-SSE sequence near a highly coupled segment along the Ecuadorian subduction zone. GPS data reveal that a one-week long SSE developed along the subduction interface at shallow depth (5–15 km) with an equivalent moment magnitude (Mw) of 6.3. During that period, a local temporary seismic network recorded >700 earthquakes with magnitudes ranging between 1.0 and 4.6. The distribution of seismicity illuminates a steep intraslab fault downdip of an oceanic relief, striking almost parallel to the trench. This seismicity migrates along strike of this active structure at a velocity of 10–15 km/day. This velocity is commonly observed in the case of slow slip propagation. Our observation suggests that the interplate SSE might have triggered a slow slip along the the intraslab active structure, which in turn drove the intraslab seismicity. In addition, at the northern part of the intraslab faults, a cluster of seismicity shows a radial expansion compatible with a fluid diffusion process. Overall, our study highlights the dynamical interaction between an interplate slow slip and an intraslab seismic swarm with the interplay of an intraslab aseismic slip propagation and fluid diffusion, both controlling the migration of seismicity. •Synchronous Slow Slip Event and seismic swarm document multiple physical processes on shallow portion of subduction zone.•Subvertical crustal cluster in-slab is synchronous to the acceleration phase of interplate SSE.•Its seismicity pattern agrees with the propagation of an in-slab slow slip rupture.•Velocity migration of a later cluster is consistent with pore pressure diffusion processes.