Precise structure at the top of subducted plate and its relationship with the plate dynamics revealed by integrated interpretation for controlled source seismic data

2018 Fiscal Year Final Research Report

• Project/Area Number: 15K05264
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Solid earth and planetary physics
• Research Institution: The University of Tokyo
• Principal Investigator: IWASAKI Takaya 東京大学, 地震研究所, 教授 (70151719)
• Project Period (FY): 2015-04-01 – 2019-03-31
• Keywords: プレート境界構造 / 反射波 / プレート境界摩擦特性 / 制御震源地震探査 / 波形解析 / 波線理論

Outline of Final Research Achievements

This study aimed at developing integrated analysis method to determine the fine structure at the top of the subducted plate boundary. My method is based on the asymptotic ray theory, which was efficiently improved in this study to realize high accuracy and stability for evaluating both the travel times and amplitudes in the complex structure models. Seismic data collected in the Kii Peninsula in 2006 were reinterpreted by my method. The results obtained indicate the detailed structural variation at the top of the Philippine Sea plate and structures of the MTL and accretionary complexes in the overriding SW Japan arc crust. The reflection property at the plate boundary is significantly changed from its seismogenic part to the steady slip part. The structure in the SE Japan arc is characterized by the northward dipping reflectors. Particularly, the Sanbagawa metamorphic belt is composed of xx-km thick reflectors, whose top corresponds to the MTL.

Free Research Field

制御震源地震学

Academic Significance and Societal Importance of the Research Achievements

本研究では，制御震源データの総合波形解析法によって，プレート境界の精密な構造推定を行うことを目指し，人工震源からの幾何学的減推を正しく評価し，プレート境界面における反射特性を求める手法を開発した．この手法は，プレート境界域にとどまらず，様々な地質構造の領域でも適用できるものである．
本研究では，紀伊半島下のプレート境界の形状，そこでの反射特性を求めた．このような知見は，単にプレート境界構造だけでなく，この領域で発生する巨大地震の理解に貢献するものである．また，上盤側島弧において明らかになった構造は，島弧地殻発達のプロセスの理解に重要である．