DI012-0008
Upper Mantle P-wave Velocity Structure beneath the Oldest Pacific Ocean Basin from Finite-frequency P-wave Traveltime Tomography
Thursday, 10 December 2020
Poster
Hyunsun Kang, Seoul National University, Seoul, Korea, Republic of (South), Younghee Kim, Seoul National University, School of Earth and Environmental Sciences, Seoul, Korea, Republic of (South), Shu-Huei Hung, Natl Taiwan Univ, Taipei, Taiwan, PeiYing Patty Lin, Department of Earth Sciences, National Taiwan Normal University, Taipei, Taiwan, Takehi Isse, The Univ. of Tokyo, Tokyo, Japan, Hajime Shiobara, The University of Tokyo, Tokyo, Japan, Hitoshi Kawakatsu, Earthquake Research Institute, The University of Tokyo, Tokyo, Japan, Sang-Mook Lee, Seoul National Univ, School of Earth and Environmental Sciences, Seoul, South Korea, Hisashi Utada, Univ Tokyo, Tokyo, Japan, Nozomu Takeuchi, Univ of Tokyo, Ocean Hemisphere Research Center, Tokyo, Japan and Hiroko Sugioka, Kobe University, Graduate School of Science, Hyogo, Japan
Abstract:
Oldest-1 array, consisting of 12 broadband ocean-bottom seismometers (BBOBS) and 7 electro-magnetometers (OBEM), was deployed in 2018-2019 on the 7°x7° area of the oldest Pacific basin (age of ~170 Ma). This experiment was conducted as a collaboration between South Korea and Japan to investigate an early evolution of the oldest Pacific plate, which is a part of the Pacific Array, an international project among several countries.
In this study, we perform finite-frequency traveltime tomography to elucidate the lithospheric-scale seismic structure from the 11 BBOBS data. We measure relative traveltime residuals of P phase of 89 teleseismic events in multiple frequency bands within 8 – 32 s from multichannel cross-correlation. The estimated P-wave traveltime residuals shows a variation of up to ±1 s across the Oldest-1 array. We observe bimodal distribution with early arrival times in the southwest and late arrivals in the northeast of the array site. The checkerboard test results with 17×17×17 nodes show that horizontal resolution of our model is 200 km, and vertical resolution is 300 – 400 km down to 900 km depth. Our preliminary P-wave velocity structure shows slow velocity anomalies at 200 – 500 km depth below northeast of the array site.
