Impact of outer-rise slab hydration on the intermediate-depth seismicity: Evidence from near field OBS observation in the southernmost Mariana subduction zone

Intermediate-depth earthquakes (IDEs), i.e., earthquakes at depths of 70 to 300 km, have been observed in subduction zones globally and extensively investigated. However, the seismogenic mechanism of IDEs is still controversial, especially in the southern end of the Mariana Trench, where near-field observations are lacking. By using machine-learning-based methods in three sets of near-field Ocean Bottom Seismogram (OBS) network data, we detected and located more than 1,000 intraplate and interplate earthquakes. The seismogenic volumes in different regions of the subducted plate are different, showing the character of double seismogenic zones (DSZ) and single seismicity layer (SSZ). The seismicity features coincide well with the regional landform, development of outer-rise faults, and hydration scenarios, suggesting a dehydration-related mechanism for the generation of IDEs. The subducted slabs experience different degrees of slab hydration, leading to various seismic behaviors.