Elucidation of low-activity active fault, targeting small surface ruptures associated with the 2016 Kumamoto earthquake

2020 Fiscal Year Final Research Report

• Project/Area Number: 17H04730
• Research Category: Grant-in-Aid for Young Scientists (A)
• Allocation Type: Single-year Grants
• Research Field: Geography
• Research Institution: Tokyo Metropolitan University
• Principal Investigator: Ishimura Daisuke 東京都立大学, 都市環境科学研究科, 助教 (00736225)
• Project Period (FY): 2017-04-01 – 2021-03-31
• Keywords: 2016年熊本地震 / 活断層 / 低活動度活断層 / トレンチ調査 / 古地震 / テフラ

Outline of Final Research Achievements

In this study, we conducted paleoseismic trenching surveys at two sites where small displacements appeared along faults far from the principal fault (Futagawa fault) that caused the 2016 Kumamoto earthquake. We investigated whether the faults with small displacements had moved at the same time as the Futagawa fault in the past. The results were consistent with the paleoseismic history of the Futagawa fault at both sites. This means that a low-slip-rate active fault can be triggered with adjacent high-slip-rate active faults like the Futagawa fault. From these facts, we are able to demonstrate a new style of activity of low-slip-rate active faults.

Free Research Field

変動地形学・第四紀地質学

Academic Significance and Societal Importance of the Research Achievements

低活動度の活断層は，単独では長い周期で地震を発生させ，地表に変位を生じさせると考えられ，その地震や変位に対するリスクは低く見積もられがちであった．しかし，本研究では，低活動度活断層の中でも周囲に高活動度の活断層がある場合には，その高活動度活断層の活動に誘発されて低活動度活断層が変位することを示した．このことは，低活動度活断層の多様性を示すとともに，従来の考えに比べて，高い頻度で地表に変位をもたらすことを意味する．今後，このような多様性を実証的な情報をも基に検証することで，より現実的な活断層による変位ハザードの評価に繋がることが期待される．