Journal Article Tomographic image of crust and upper mantle off the Boso Peninsula using data from an ocean-bottom seismograph array

Ito, Aki  ,  Yamamoto, Yojiro  ,  Hino, Ryota  ,  Suetsugu, Daisuke  ,  Sugioka, Hiroko  ,  Nakano, Masaru  ,  Obana, Koichiro  ,  Nakahigashi, Kazuo  ,  Shinohara, Masanao

69p.118 , 2017-08-24 , SpringerOpen
We determined the three-dimensional structure of the crust and upper mantle off the Boso Peninsula, Japan, by analyzing seismograms recorded by ocean-bottom seismometers and land stations between 2011 and 2013. We employed seismic tomography to determine the P-and S-wave velocity structures and earthquake locations simultaneously. The tomographic image shows that the mantle parts of the Pacific and the Philippine Sea plates have high-velocity anomalies. The upper boundary of the Philippine Sea plate is delineated as approximately 2-6 km shallower than that previously estimated from land-based data for the area 140.5°E-141.5°E and 35°N–35.5°N. A pronounced low-velocity anomaly in P-and S-waves with low-V-p/V-s ratio (1.5-1.6) was observed at depths shallower than 20 km in the overriding North American plate. This anomaly may be caused by the presence of rocks with a low-V-p/V-s ratio, such as quartzite, and the water expelled from the subducted Pacific and Philippine Sea plates.

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