3D Local Earthquake Tomography of the Ecuadorian Margin in the Source Area of the 2016 Mw 7.8 Pedernales Earthquake

• Published in: Journal of geophysical research. Solid earth 2021-03, Vol.126 (3), p.n/a
• Main Authors: León‐Ríos, Sergio, Bie, Lidong, Agurto‐Detzel, Hans, Rietbrock, Andreas, Galve, Audrey, Alvarado, Alexandra, Beck, Susan, Charvis, Philippe, Font, Yvonne, Hidalgo, Silvana, Hoskins, Mariah, Laigle, Mireille, Oregioni, Davide, Meltzer, Anne, Ruiz, Mario, Woollam, Jack
• Format: Article
• Language: English
• Subjects: aftershocks; Earth Sciences; Ecuador; Geophysics; megathrust earthquake; Sciences of the Universe; seismic tomography; subduction zone; velocity structure
• ISSN: 2169-9313; 2169-9356
• DOI: 10.1029/2020JB020701

Based on manually analyzed waveforms recorded by the permanent Ecuadorian network and our large aftershock deployment installed after the Pedernales earthquake, we derive three‐dimensional Vp and Vp/Vs structures and earthquake locations for central coastal Ecuador using local earthquake tomography. Images highlight the features in the subducting and overriding plates down to 35 km depth. Vp anomalies (∼4.5–7.5 km/s) show the roughness of the incoming oceanic crust (OC). Vp/Vs varies from ∼1.75 to ∼1.94, averaging a value of 1.82 consistent with terranes of oceanic nature. We identify a low Vp (∼5.5 km/s) region extending along strike, in the marine forearc. To the North, we relate this low Vp and Vp/Vs (1.85) which we interpret as deeply fractured, probably hydrated OC caused by the CR being subducted. These features play an important role in controlling the seismic behavior of the margin. While subducted seamounts might contribute to the nucleation of intermediate megathrust earthquakes in the northern segment, the CR seems to be the main feature controlling the seismicity in the region by promoting creeping and slow slip events offshore that can be linked to the updip limit of large megathrust earthquakes in the northern segment and the absence of them in the southern region over the instrumental period. Plain Language Summary Using seismic data recorded by the permanent Ecuadorian network and the large emergency installation after the 2016 Pedernales earthquake, we obtained the seismic velocity structure together with precise earthquake locations for the coastal Ecuadorian margin. Our images highlight the heterogeneities of the subduction zone affected by seamounts and ridges comprising the oceanic crust. These features play an important role in controlling the seismic behavior of the margin. While seamounts can contribute to the occurrence of intermediate (M ∼ 7–7.5) megathrust earthquakes in the north, the Carnegie Ridge seems to be the main feature controlling the seismicity in the region by promoting creeping and slow slip events offshore that can be linked to the updip limit of large megathrust earthquakes in the northern segment and the absence of them in the southern region. Key Points 3D Vp and Vp/Vs models were calculated using local earthquake tomography in the region affected by the 2016 Pederna