The 16 April 2016, M_W 7.8 (M_S 7.5) Ecuador earthquake: A quasi-repeat of the 1942 M_S 7.5 earthquake and partial re-rupture of the 1906 M_S 8.6 Colombia–Ecuador earthquake

The 2016 Ecuador M _W 7.8 earthquake ruptured the subduction zone boundary between the Nazca and South American plates. Joint modeling of seismic and tsunami observations indicates an ∼120 km long rupture area beneath the coastline north of the 1998 M_W 7.2 rupture. The slip distribution reveals two discrete asperities near the hypocenter and around the equator. Their locations and the patchy pattern are consistent with the prior interseismic geodetic strain, which showed highly locked patches also beneath the coastline. Aftershocks cluster along two streaks, one aligned nearly parallel to the plate convergence direction up-dip of the main slip patches, and the other on a trench-perpendicular lineation south of the 1958 rupture zone. Comparisons of seismic waveforms and magnitudes show that the 2016 event and 1942 earthquakes have similar surface wave magnitude M_S 7.5), overlapping rupture areas, and similar main pulses of moment rate. The same area ruptured as the southernmost portion of the larger earthquake of 1906 (M_W 8.6, M_S 8.6). The seismic behavior reflects persistent heterogeneous frictional properties of the Colombia–Ecuador megathrust.