Why did the Kumamoto earthquake stop within the Aso Caldera?: Termination of fault rupture explored by geodetic observation and numerical simulation

2022 Fiscal Year Final Research Report

• Project/Area Number: 18K03810
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 17040:Solid earth sciences-related
• Research Institution: Geospatial Information Authority of Japan (Geography and Crustal Dynamics Research Center)
• Principal Investigator: Kobayashi Tomokazu 国土地理院(地理地殻活動研究センター), その他部局等, 研究室長 (40447991)
• Co-Investigator(Kenkyū-buntansha): 安藤 亮輔 東京大学, 大学院理学系研究科(理学部), 准教授 (10455256) ; 松尾 功二 国土地理院(地理地殻活動研究センター), その他部局等, 主任研究官 (80722800) ; 中埜 貴元 国土地理院(地理地殻活動研究センター), その他部局等, 研究官 (60511962)
• Project Period (FY): 2018-04-01 – 2023-03-31
• Keywords: 断層破壊の停止 / 内陸地震 / 火山 / 地殻変動 / ＳＡＲ / 重力 / 密度構造 / 3次元動的破壊数値シミュレーション

Outline of Final Research Achievements

Conducting crustal deformation analysis using synthetic aperture radar satellite data, we have successfully revealed that the fault slip for the 2016 Kumamoto earthquake progressively converged just after penetrating a few km into the Aso caldera. We inferred the density contrast structure using gravity data, and found that a low-density body exists in the shallow part of the western edge of the caldera at a depth of a few km. The fault slip penetrated the low-density region, and then dissipated. It is suggested that a hydrothermal environment has developed in the region, resulting in a high-temperature crustal structure which could prevent from further brittle rupture. Our numerical simulation of dynamic rupture indicates that the presence of low stress field in the caldera is closely related to the terminus of fault rupture.

Free Research Field

地震学

Academic Significance and Societal Importance of the Research Achievements

内陸地震における断層末端のすべりの様子とその周囲の地殻構造を従来にない高い空間分解能で捉えたことにより、火山地域における高温の地熱地帯が断層破壊の停止に強く関与していたことを明らかにした。このことは、地震と火山の相互作用が断層破壊の停止の要因を考える上で重要な視点となり得ることを当該研究分野に示すものである。