2016 Ecuador earthquake and rupture mode along the Ecuador-Colombia subduction zone

A large earthquake (Mw 7.7) occurred on 16 April 2016 within the source region of the 1906 earthquake, which has been interpreted as a megathrust earthquake (Mw 8.8) that ruptured the source regions of smaller earthquakes in 1942 (Mw 7.8), 1958 (Mw 7.7), and 1979 (Mw 8.1). We analyzed the mainshock and aftershocks of the 2016 earthquake using regional broadband seismic data in Ecuador and Colombia. We performed teleseismic slip inversion of the mainshock of the 2016 earthquake using waveform data from the global broadband seismic networks. Our CMT inversion of the 2016 earthquake indicated an Mw 7.7 event with a dip-slip mechanism at a depth of 25 km. Our slip inversion indicated that the rupture propagated from north to south with the maximum slip of 2.2 m. CMT solutions of the aftershocks were characterized dominantly by dip-slip mechanisms, and large aftershocks occurred north and south of the mainshock slip region at shallow depths. The spatial distribution of the 2016 earthquake and its aftershocks correlated with patches of high interplate coupling strength and was similar to the distribution of the 1942 earthquake and aftershocks, suggesting that the 2016 earthquake ruptured the same asperity as the 1942 earthquake for a recurrence interval of 74 years. If this asperity was ruptured by the 1906 earthquake, the 1942 earthquake occurred only 36 years after the 1906 earthquake. Yoshimoto and Kumagai [2016 AGU Meeting] performed tsunami waveform inversion of the 1906 earthquake, which indicated Mw around 8.4 and showed that the main slip occurred near the trench off the source regions of the three historical and 2016 earthquakes. The tsunami inversion results indicate that the 1906 earthquake did not rupture the source region of the 1942 earthquake, which explains the discrepancy in the recurrence interval. These results suggest that the existence of a depth-dependent complex rupture mode along the Ecuador-Colombia subduction zone.