[J08-P] Poster

[J08-P-15] Three-dimensional P- and S-wave attenuation tomography in the Ryukyu Arc, Japan

^○Masanao Komatsu, Hiroshi Takenaka (Graduate School of Natural Science and Technology, Okayama University, Okayama, Japan)

We investigate 3D seismic Qp and Qs structures in the Ryukyu Arc. It is important to estimate the 3D Q structure in this region, since there are highly active volcanoes and seismicity between the Okinawa Trough and the Ryukyu Trench. We use seismic waveform data recorded by seismic observation networks of NIED, JMA and Kagoshima University, from 2004/06 to 2014/05. We select 4,353 seismic events, which the range of JMA magnitude is greater than or equal to 3.0 and less than or equal to 6.0. The corner frequency of the source spectrum for each event is estimated by using scaling law before calculating the attenuation quantity t*. The t* is estimated from the amplitude decay rate from the source-corrected spectra between 3.0-30.0 Hz. 21,089 P- and 17,939 S-wave t* are obtained. We then invert the P- and S-wave t* data to 3D Qp and Qs distributions by a tomographic technique using the non-negative least squares method. For the inversion, the coordinate center is located at (127.0E, 26.5N). The coordinate system is rotated counterclockwise 42 degrees from north. We confirm that this axis rotation can improve the result of the checkerboard resolution tests (CRTs). Our estimated Qp and Qs structures has remarkable features: low-Qp and Qs zones exist beneath the Okinawa Trough, where is an extensional field along the rift. Low-Qp and Qs patches are located beneath active volcanoes in the Tokara islands. These patches may indicate upwelling of high temperature materials from top of the high-Qp and Qs Philippine Sea (PHS) slab. Low-Qp and Qs spots are also located in the forearc side. Especially, these spots in Kikai Island and Hateruma Island may denote sediment or accretionary prism.