S-wave attenuation tomography of upper crust in Japan

Seismic attenuation (Q-factor) can be estimated by extracting the amplitude-frequency information contained in seismic waveforms. We applied M-L amplitude tomography to estimate attenuation of upper crust in Japan. More than 60000 Sg-wave maximum amplitude data from 5559 events recorded by 971 stations were selected from the dense High-Sensitivity Seismographic Network (Hi-net) under the condition that epicentral distance is less than 2 degrees; event depth is less than 10km. The lateral S-wave Q-factor variations of upper crust at 1Hz in Japan were obtained, and the result indicates that the low Q values exist in the central Japan islands, and have almost the same distribution with volcanoes; the low-Q zones also exist in non-volcanic regions at the Kyoto and Kobe prefectures, and eastern Shikoku with dense faults there; in addition, low Q was found between eastern coast and Japan trench. These suggest that the high attenuation (low Q value) results from high temperature, cracked rocks and thick sediment. The high Q values mainly exist between the front of volcanoes and the Japanese east coast.