スペクトルインバージョンによって推定された関東地域の三次元S波減衰構造

The Kanto region, Japan, has often been hit by large earthquakes, such as the 1855 Ansei-Edo Earthquake and the 1923 Kanto Earthquake, and has been damaged by strong seismic ground motion. The distribution pattern of strong ground motion, or seismic intensity, in this region depends on the location of the hypocenter because the three-dimensional seismic wave attenuation structure is complex due to the dual subduction system by the Philippine Sea and the Pacific slabs. Since the S-wave attenuation structure (QS) particularly affects the amount of the ground motion and seismic intensity, the Qs structure is essential for seismic hazards in and around the Kanto. In this study, therefore, we examined the three-dimensional Qs structure in and around the Kanto using the short-period (1-10 Hz) seismic motions. The resultant detailed Qs structure reconfirmed the presence of strong attenuation (low-Qs) zone at the depths of 20-40 km, which lay east to west beneath the border of Ibaraki and Chiba prefectures. Another low-Qs zone was detected beneath the Boso peninsula, reflecting the serpentinization of the easternmost part of the subducting Philippine Sea slab mantle. The three-dimensional Qs structure obtained in this study will improve seismic intensity predictions for earthquakes that occur in and around the Kanto region and will contribute to investigations of hypocenter locations of historical earthquakes.