[S-IT20] MAGMA, FLUID TRANSPORT, AND SEISMICITY IN THE EARTH'S INTERIOR

[SIT20-11] Attenuation contrast in mantle wedge across the volcanic front of NE Japan that controls propagations of high-frequency S-wave later phases

*Takahiro Shiina¹, Kei Katsumata², Kiyoshi Yomogida², Aitaro Kato³ (1.National Institute of Advanced Industrial Science and Technology (AIST), 2.Graduate School of Science, Hokkaido University, 3.Earthquake Research Institute, the University of Tokyo)

Keywords:Later phase, Intraslab earthquake, S-wave attenuation, Scattering

Distinct later phases of waves containing high-frequency (>8 Hz) components were observed for intraslab earthquakes that occurred at intermediate depths, particularly at depths exceeding 100 km, in the NE Japan subduction zone. These high-frequency later phases showed anomalously large peak-amplitude delays, up to ~50 s after direct S-wave arrivals at stations in the backarc region. Using a source-scanning algorithm, we investigated the locations of passing points affecting the propagation of high-frequency later phases. The passing points were estimated to be in the forearc region in the entire NE Japan, indicating that high-frequency later phases are scattered waves that pass through the forearc region. The propagating high-frequency later phases seem to bypass the backarc mantle wedge, as a consequence of the distinct attenuation contrast in the mantle wedge across the volcanic front in NE Japan. These high-frequency later phase observations suggest that the high-attenuation zone in the backarc mantle wedge controls propagations of the high-frequency waves of intraslab earthquakes, in addition to the scatterers possibly locate in the forearc region.