JpGU-AGU Joint Meeting 2017

講演情報

[EE] ポスター発表

セッション記号 S (固体地球科学) » S-IT 地球内部科学・地球惑星テクトニクス

[S-IT25] [EE] New constraints on the asthenosphere and its role in plate tectonics

2017年5月20日(土) 15:30 〜 17:00 ポスター会場 (国際展示場 7ホール)

コンビーナ:William Bythewood Hawley(University of California Berkeley)、川勝 均(東京大学地震研究所)、日置 幸介(北海道大学大学院理学研究院地球惑星科学部門)、Thorsten W Becker(Jackson School of Goesciences, The University of Texas at Austin)

[SIT25-P05] Waveform modeling of BBOBS data for old oceanic lithosphere-asthenosphere system

*丸山 純平1竹内 希1川勝 均1 (1.東京大学地震研究所)

Analysis for a base of lithosphere, at nearly 100 km depth, is still difficult because of a lack in observation data which contain a pure information for the lithosphere-asthenosphere system (LAS). Recent developments in seafloor in-situ observation and waveform analysis enable to determine more detailed structure of the LAS. In this study, we modeled broadband seismic waveforms of outer-rise earthquakes occurring after the Tohoku earthquake around the Japan trench that are observed by 5 broad-band ocean bottom seismometers(BBOBSs) at the northwest pacific seafloor; the traveling paths of these seismic waves are entirely within the old (~130Ma) ocean LAS, and can be used to constrain the average 1-D velocity structure under ’normal ocean’. Because the observation data contain much short-period noise, the waveforms need to be applied appropriate bandpass filters: periods 6-100s for P wave, 33-100s for Rayleigh wave, and many octave-range filters for Love wave. We compared observed and synthetics waveforms, and then adjusted our model. Very preliminary analysis indicated that (1) crust is 3% faster in P wave or 0.5 km thinner than the PA5 model (Gaherty et al., 1999), (2) LID is 20km thicker or 2% slower than PA5, but (3) the model has still strong trade-off between crust thickness and crust velocity, and between LID thickness and LID velocity. As a result, the depth of lithosphere-asthenosphere boundary (LAB) or G-discontinuity is not constrained uniquely. Further analysis for multiply bounced S-waves (e.g., ScS, SS, SSS) should constrain more detailed structure for the depth.