Double seismic zone and seismicity in the mantle wedge beneath the Ogasawara Islands identified by an ocean bottom seismometer observation

A double seismic zone, characterized by two distinct planes separated by approximately 30–35 km within the subducting Pacific slab beneath the Ogasawara Islands, has been identified through a temporary ocean bottom seismometer (OBS) network deployed from July to October 2015. This finding aligns with similar observations at other trenches like Japan and Mariana, suggesting consistent geological structures in subduction zones. Additionally, the study revealed unusual seismicity in the mantle wedge at depths of 20–50 km beneath the Ogasawara trough, potentially linked to structural formations at the onset of oceanic slab subduction. The OBS network provided more precise hypocenter locations, horizontally separated by tens of kilometers from previously published data, including those from the Seismological Bulletin of Japan and USGS, which were found to be offset westward by about 30 km.

Nakata, K., Kobayashi, A., Katsumata, A., Hirose, F., Nishimiya, T., Kimura, K., Tsushima, H., Maeda, K., Baba, H., Hanamura, N., Yamada, C., & Kanezashi, M. (2019). Double seismic zone and seismicity in the mantle wedge beneath the Ogasawara Islands identified by an ocean bottom seismometer observation. Earth, Planets and Space, 71(1). https://doi.org/10.1186/s40623-019-1012-z