3D P-wave velocity structure of the Northern Ecuadorian seismogenic zone, host to the 2016 M7.8 Pedernales earthquake.

In Ecuador, in the vicinity of the seismic rupture of the 2016 Mw 7.8 Pedernales earthquake, the megathrust fault is also affected by aseismic slip at shallow depths, including slow earthquakes and post-seismic slow slip. 

The Ecuadorian margin is an exceptional natural laboratory. Its relatively narrow marine forearc and shallow megathrust make it an ideal location for studying the relationship between ongoing subduction of topographic highs, such as ridge and seamount, and seismic and aseismic slip behaviour on the plate interface.

The HIPER Project (2020–2022), which aims to better characterize the 3D structure of the Ecuadorian forearc domain, is based on an international collaboration funded by the French Oceanographic Fleet, the French ANR, Karlsruhe Institute of Technology (KIT, Germany), American NSF and IG-EPN (Ecuador). We successfully deployed a large number of OBSs (47), land stations (~200) and nodes (~500) to record both R/V L’Atalante shots and seismic activity.

Here, we present preliminary results from a 3D inversion of P-wave refraction and reflection data, which was performed with TOMO3D. Thanks to our newly developed semi-automatic picking tool, DeepFB, we were able to efficiently compile the catalogue of ~230,000 picks.. DeepFB is a U-Net based neural network designed for robust automatic first-break picking in active-source seismic data. It was extensively applied to our dataset and accounts for approximately 50% of the picked first arrivals. The resulting 3D P-wave velocity model provides new insights into the lateral velocity variations of the Ecuadorian margin and the subducting plate along the trench between latitudes 1°25′N and 0°10′S.