Study on a practical fault dip estimation method using a gravity gradient tensor

2021 Fiscal Year Final Research Report

• Project/Area Number: 17K01325
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Natural disaster / Disaster prevention science
• Research Institution: Kyoto University (2020-2021); University of Toyama (2017-2019)
• Principal Investigator: Kusumoto Shigekazu 京都大学, 理学研究科, 教授 (50338761)
• Project Period (FY): 2017-04-01 – 2022-03-31
• Keywords: 断層傾斜角 / 重力偏差テンソル / 伏在断層 / 活断層

Outline of Final Research Achievements

This study showed that fault type of an arbitrary buried fault could be determined by the combination of the horizontal gradient of the gravity anomaly and the maximum eigenvalue of the gravity gradient tensor. After determining the fault type, we can estimate the fault dip for a normal fault by the maximum eigenvector of the gravity gradient tensor and the dip for a reverse fault by the minimum eigenvector of the tensor, respectively.
As fundamental indicators or development of a technique for quantitatively evaluating the depth direction reliability of the fault dip estimated by the gravity gradient tensor, the relationships between the pseudo-depth of the causative layer and the power spectrum of each of the six components of the gravity gradient tensor due to the layer were derived. In addition, we suggested an algorithm estimating the pseudo-depth of the causal layer from the power spectrum of gravity anomaly automatically.

Free Research Field

テクトニクス・物理探査

Academic Significance and Societal Importance of the Research Achievements

断層やカルデラ壁といった構造境界の傾斜角は，それらの形成メカニズムを議論するうえで重要な役割を果たすだけでなく，ハザードマップ作成時にも重要な役割を果たす。特に断層傾斜角は，地震時の被害状況予測に不可欠な強震動シミュレーションで重要な意味をもつ。しかしながら，大規模地震波探査といった高額な探査手法は別として，実際の断層傾斜角の見積もりでは，既存の探査・解析手法では難しい。このようなことを考えた場合，重力偏差テンソルの固有値，固有ベクトルを用いた断層タイプの判定と断層傾斜角推定の自動化は，地球科学やその周辺分野および応用分野に及ぼす意義は大きい。