Study on improvement estimation of site effect of seismic waves and validation of underground velocity structure model

2023 Fiscal Year Final Research Report

• Project/Area Number: 20K05044
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 25030:Disaster prevention engineering-related
• Research Institution: Kyoto University
• Principal Investigator: Iwata Tomotaka 京都大学, 防災研究所, 教授 (80211762)
• Co-Investigator(Kenkyū-buntansha): 染井 一寛 一般財団法人GRI財団, その他部局等, 研究員 (40750584)
• Project Period (FY): 2020-04-01 – 2024-03-31
• Keywords: スペクトルインバージョン / 地震波サイト増幅特性 / 震源特性 / 伝播経路特性 / 地盤構造モデル / 破壊伝播速度 / 応力降下量 / 珠洲市正院

Outline of Final Research Achievements

A new formulation of the spectral inversion method including finite source fault effects in the source characteristics is developed and applied to the strong motion data of the 2016 Kumamoto earthquake sequence. The parameters of rupture propagation direction, rupture velocity, and rupture pattern are estimated. It is found that the source parameter estimation can be obtained reliably when station coverage are fine. When the stress drop was estimated based on the source terms estimated by this method, the distribution of the stress drop was less varied than that by the conventional method, but the characteristics of each event (magnitude, depth, and location) remained.
Using the obtained site amplification factor of each station obtained by the spectral inversion, we assumed that the site amplification was caused by the underground velocity structure below the station and validated the existing underground velocity structure model.

Free Research Field

強震動地震学

Academic Significance and Societal Importance of the Research Achievements

強震観測点の増加により、多数の波形データを使う環境が整ってきている。従来の地震波特性の分析手法を高度化し、震源特性及びサイト増幅特性を複数のパラメータにおいて分析するための定式化を行うことで、従来より詳細な震源特性とサイト増幅特性を求めることができる。震源特性は将来起きる地震像の拘束に利用され、サイト増幅特性は、強震動予測に必要な地盤構造モデルの高度化に活用でき、これらにより将来起きる地震時の強い揺れの予測精度を上げ、地震被害の軽減につなげることができる。