Along-strike variations in intermediate-depth seismicity in the southernmost Mariana subduction zone: Impact from the subduction of an oceanic plateau

Abstract

Intermediate-depth earthquakes, i.e., earthquakes occurring at depths of 60 to 300 km, have been observed globally. However, the mechanisms underlying intermediate-depth earthquakes and their potential relationship with shallow subduction zone structures are still poorly understood. Utilizing newly obtained near-field Ocean Bottom Seismometer (OBS) data and a machine-learning-based method (EQTransformer), we have detected and located 613 earthquakes from 5 September 2018 to 22 October 2019. The observation identifies the variations in the distribution patterns of intermediate-depth earthquakes at the junction of the Pacific plate and the Caroline Plateau. Double seismic zones (DSZs) were observed in the Pacific segment, while a single seismic zone (SSZ) was found in the Caroline segment. The consistency between observed seismicity patterns, tectonic geomorphology, outer-rise faulting, and slab P-T modeling strongly suggests intermediate-depth earthquakes are likely related to the dehydration of hydrous minerals. We propose that the seismicity difference between the two segments is attributed to the subducted oceanic plateau, which restricts hydration of the subducting plate thereby suppressing the generation of intermediate-depth earthquakes. Our results emphasize the important influence of oceanic plateau subduction in the generation and distribution of intermediate-depth earthquakes.