High variability of stress accumulation, seismic and aseismic release mode along the Peru-Ecuador subduction zone (Invited)

Most geodetic measurements of interseismic strain along subduction zones have led to the view of coupled asperities of variable size usually separated by narrower zones of low coupling. Along the western margin of South America, fast convergence of the oceanic Nazca plate has repeatedly produced M>8 earthquakes and three of the ten largest megathrust earthquakes since 1900. Contrasting with this behavior, the segment comprised between central Peru and central Ecuador has not experienced any great earthquake for at least five centuries. New GPS measurements in Peru and Ecuador first highlight that a along a ~1000km long segment, convergence is predominantly accommodated by aseismic creep along the plate interface, with possible coupling occurring at shallow depth, close to the trench. This area is bounded by highly locked segments, which produced M>8.5 earthquakes in central Peru and northern Ecuador. While the observed low interseismic coupling explains the lack of great earthquakes, this area has experienced two earthquakes that share the characteristics of tsunamigenic earthquakes, indicating a correlation between the mode of stress accumulation along the plate interface and its release. Finally, we have observed several episodes of slow slip, sometimes associated with intense, micro to moderate seismicity. These observations suggest a specific behavior for this segment, which contrasts with the behavior of the neighboring segments.