Earthquake generation mechanism based on fault conditions inferred from the rupture process of small earthquakes

2023 Fiscal Year Final Research Report

• Project/Area Number: 20K14569
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 17040:Solid earth sciences-related
• Research Institution: Tohoku University
• Principal Investigator: Yoshida Keisuke 東北大学, 理学研究科, 助教 (20743686)
• Project Period (FY): 2020-04-01 – 2024-03-31
• Keywords: 放射エネルギー / 複雑性 / モーメントレート関数 / 震源パラメータ / 応力降下量 / 放射効率 / 断層状態

Outline of Final Research Achievements

Since 1970, many efforts have been made to estimate the source parameters of small earthquakes. For this purpose, the rupture process and source spectra of small earthquakes were approximated by some specific simple models. However, if there is in fact complexity and diversity in the rupture process and source spectra of small earthquakes, the validity of the results obtained by the above approach may become questionable. In this study, we systematically investigate the rupture processes of small earthquakes using high-quality Japanese seismic data and show that there is great diversity in the rupture processes in small earthquakes. It is easy to find cases where conventional source models cannot be applied. We show that the use of radiated energy as a source parameter of small earthquakes makes it possible to characterize their properties without using assumptions on their source processes.

Free Research Field

地震学

Academic Significance and Societal Importance of the Research Achievements

日本列島の高品質な地震データを用いることにより、大地震だけでなく小地震の破壊過程の多様性を直接推定できることを示した。その結果は、小地震の破壊過程も大地震のそれと同等の複雑性を有している可能性を示し、従来世界中で用いられてきた小地震の震源パラメータ推定手法に大きな問題があることを示した。これまで推定されてきた小地震の特徴量の代替として、地震波の放射エネルギーが使用可能であることを示した。