[S22]AM-2

[S22-02] Vs structure of the shallow crust beneath ocean-bottom seismometers: south and north Okinawa trough

〇Ban-Yuan Kuo¹, Pei-Ru Jian¹, Pei-Ying Patty Lin², Ching-Ren Lin¹, Yasushi Ishihara³, Shuichi Kodaira³, Mamoru Nakamura⁴, Chau-Chang Wang⁵ (1.Institute of Earth Sciences, Academia Sinica, 2.National Taiwan Normal University, 3.JAMSTEC, 4.University of the Ryukyus, 5.NARLabs)

We employ a P-wave polarization method to estimate the Vs of the shallow crust beneath ocean-bottom seismometer (OBS) arrays in Okinawa trough. In comparison, we applied this method to F-net in the Tohoku region, Japan. We found that the seafloor beneath OBSs is characterized by Vs of hundreds of m/s, while Vs of the shallow crust of Tohoku is typically 2-4 km/s with the about 1 km/s at volcano sites. The OBSs along the Okinawa trough were probably deployed on the very soft oceanic crust first layer composed of young, uncompact sediment. The observed Ps following the P phase attests to this hypothesis. We are in the process of extending this research to OBSs on old seafloor of the Pacific basin.