Slip distribution of the 2015 Mw 8.3 Illapel, Chile earthquake constrained by geodetic and seismological observations

On 16 September 2015, a magnitude Mw 8.3 interplate thrust earthquake ruptured a densely instrumented region in central Chile. The abundant datasets near and around the rupture zone provide a unique opportunity to study the detailed source process of this megathrust earthquake. We investigated the spatial and temporal distributions of the mainshock by a joint inversion of geodetic and seismological observations. Our optimized model shows that the primary slip zone is located in the north of the hypocenter with a maximum slip of 9.2 m, and the rupture scale extends 150 km along strike and 140 km along dip. Considering the strain accumulation, the 9.2 m of peak coseismic slip largely exceeds the 4.9 m slip deficit accumulated since 1943 Mw 7.9 event assuming a full coupling. The total seismic moment is 3.04×1021N·m, equivalent to Mw 8.3. Most seismic moment was released within 140 s. The rupture propagated in main slip asperity with a velocity of 2.0 km/s. We find that the aftershocks distributions have a clear complementary distribution with the co-seismic rupture pattern, aftershock clusters are found at the edge of unbroken barriers, and regions of rapid transition from high to low slip within the main fault area. Our results reveal that the low frequency radiation is associated with the large coseismic slip at the shallower portion of the megathrust whereas the high frequency radiation corresponds to isolated patches at greater depths. Based on the Coulomb stress change caused by the main rupture, 80% of aftershocks with focal mechanism are promoted for failure.