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

•The 2016 earthquake ruptured ∼120 km along the plate boundary beneath Ecuador.•Teleseismic and tsunami modeling locates ∼2 m slip in a strongly coupled area.•The 2016 rupture zone appears to overlap that of the 1942 event.•The 2016 rupture appears to be the southern part of the 1906 zone.•The 2016 rupture terminates south of the 1958 event.

The 2016 Ecuador MW7.8 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 MW7.2 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 (MS7.5), overlapping rupture areas, and similar main pulses of moment rate. The same area ruptured as the southernmost portion of the larger earthquake of 1906 (MW8.6, MS8.6). The seismic behavior reflects persistent heterogeneous frictional properties of the Colombia-Ecuador megathrust.