The relationship between seismicity and geometry of plate interface near the trench at the western part of Guerrero seismic gap from a recent seafloor experiment

Capturing the spatial and temporal distribution of slow and fast earthquakes offshore at subduction zones becomes fundamental tasks in seismology. Ocean bottom seismometers (OBSs), especially the autonomous type, are useful to measure activities of both fast and slow earthquakes at the ocean bottom away from coastline, simply and with portability. We deployed 9 or 10 OBSs at the western part of the Guerrero seismic gap, off Mexico in two observation periods lasting one year each from 2017 to 2018 and again from 2018 to 2019, to capture both fast and slow earthquakes. Detection of fast earthquakes and their P&S arrivals picking are performed with the Earthquake Transformer (Mousavi et al., 2020). The Earthquake Transformer is applied to continuous trace of OBS records to create a bank of P&S arrivals at each station. After applying phase association for all of the picked phases using the REAL algorithm (Zhang et al., 2019), we invert their hypocenters with the Hypomh (Hirata and Matsu'ura, 1987) assuming horizontal layered seismic structure. Slow earthquakes, especially tectonic tremors, are detected with a modified envelope correlation method (Mizuno and Ide, 2019). We have proposed a silent zone, absent of fast and slow seismicity, located at the western part of the Guerrero seismic gap, where we also identified a negative anomaly on residual gravity and bathymetry, which we interpret as related to variations in the geometry of the subducting plate surface (Plata-Martinez et al., 2021). One of the major aims of reanalysing with the AI-based detector on OBS data is to test the hypothesis that the geometry of the plate interface exerts a control on the occurrence of slow-to-fast earthquakes.Nearly 2500 events in the 2017-2018 period were detected with Earthquake Transformer although approximately 500 earthquakes had been detected in the manual picking. Many events are distributed near the coastline, while they are rarely distributed within the Guerrero seismic gap. The low seismicity zone is well consistent with the negative anomaly in both residual gravity and bathymetry. The landward edge of the silent zone is also still clearly identified; the hypocenters of repeating earthquakes and micro-earthquakes are located in the silent zone.