New Hybrid Back-Projection Method and High-Frequency Radiation Events in Great Earthquake

2019 Fiscal Year Final Research Report

• Project/Area Number: 16K05529
• 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: University of Tsukuba
• Principal Investigator: YAGI Yuji 筑波大学, 生命環境系, 教授 (50370713)
• Co-Investigator(Kenkyū-buntansha): 深畑 幸俊 京都大学, 防災研究所, 准教授 (10313206)
• Project Period (FY): 2016-04-01 – 2020-03-31
• Keywords: 震源過程

Outline of Final Research Achievements

In this study, we developed a new Hybrid Back-projection (HBP) method that simultaneously estimates the focal mechanism and the high frequency radiation source, and then applied this method to great earthquakes to understand the nature of the high frequency radiation source. To obtain appropriate results with reasonable computational cost, we decided to limit the estimated fault parameters to the slip angle. Applying the new method to the to the 2008 Sichuan earthquake, we found that the high frequency radiation sources are associated with discontinuous changes of the fault geometry and the slip vectors. We also discussed the theoretical background of HBP method and proposed a new formulation for estimating the HBP results related to the slip-rate function.

Free Research Field

地震学

Academic Significance and Societal Importance of the Research Achievements

建造物にダメージを与える高周波地震動の発生の原因を理解することは、将来の地震被害を予測する上で重要であるだけではなく、地震の不規則な破壊伝播過程を理解する上でも重要である。本研究は、断層形状の変化が破壊伝播に及ぼす影響を地震波形から求める手法を開発して、実地震に適用した。本研究によって、断層形状や断層すべりが急変する領域で、高周波が励起されていることが実データの解析から明らかになった。