Effects of the seamount subduction on earthquake generation: inferred from friction experiments

2021 Fiscal Year Final Research Report

• Project/Area Number: 17K14406
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Geology
• Research Institution: Chiba University
• Principal Investigator: Sawai Michiyo 千葉大学, 大学院理学研究院, 助教 (20760995)
• Project Period (FY): 2017-04-01 – 2022-03-31
• Keywords: 海山 / 沈み込み / 地震 / 摩擦

Outline of Final Research Achievements

Subducted seamounts are traditionally thought to affect seismic faulting along a subduction zone megathrust by increasing the normal stress on the subduction interface and to act as asperities, although recent studies suggest that they can act as barriers for rupture propagation or may promote slow slip behavior or creep. In this project, we conducted friction experiments on gouges of a greenstone to reveal the frictional strength of seamounts and the effect of temperature on frictional stability and investigated how the seamounts act at subduction zones. Our results showed that at low temperatures frictional strength was notably greater than those of typical subduction zone materials, and that frictional stability decreases with increasing temperature, i.e. with increasing depth. These results suggest that a seamount may act as a barrier for rupture propagation on a shallow portion, and can be a site of earthquake nucleation on a deep portion of a subduction zone.

Free Research Field

岩石力学

Academic Significance and Societal Importance of the Research Achievements

アスペリティ形成のひとつの要因として海山が有力視され、さらにアスペリティは、海溝型巨大地震からスロー地震に至るまで多くの現象を理解するための鍵と考えられている以上、海山の摩擦特性を理解することはアスペリティと地震発生を考える上で何が鍵となるのかを紐解く一端になりうる。本研究によって、海山は深く沈み込むほど不安定な挙動を示す一方、比較的温度の低い沈み込み帯の浅い領域では安定な挙動を示すことが明らかになったが、今後、数値計算などにこのような結果から制約を与えることにより、沈み込み帯で発生する多様な地震活動に対する理解がさらに深まると期待される。