Experimental study of the high-velocity weakening of fault in quartz and its nano-scale deformation structures

2022 Fiscal Year Final Research Report

• Project/Area Number: 20H02007
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 17040:Solid earth sciences-related
• Research Institution: Kyoto University
• Principal Investigator: Tsutsumi Akito 京都大学, 理学研究科, 准教授 (90324607)
• Co-Investigator(Kenkyū-buntansha): 三宅 亮 京都大学, 理学研究科, 准教授 (10324609) ; 伊藤 正一 京都大学, 理学研究科, 准教授 (60397023)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: 岩石摩擦 / 石英岩 / 高速摩擦 / 速度弱化 / 摩擦ヒーリング

Outline of Final Research Achievements

We examined frictional properties of synthetic quartz at a constant normal stress of 1.5 MPa and at various slip velocities V of 0.005-105 mm/s under humidity conditions (0%-80%RH). It is revealed that the steady-state friction of quartz exhibits velocity-weakening behaviors at V > ~1 mm/s, while steady-state values of friction at same slip velocity increase with humidity. Humidity dependence of frictional behavior of quartz was also observed in slide-hold-slide tests performed after slip-weakening of the samples at V = 105 mm/s, in which amount of the frictional aging increases with humidity. Micro-structural observation of the fault zone under a TEM reveals that the fault-zone is composed of a number of stacked ~0.5 μm-thick ultra-thin layers of stacked amorphous silica grains. The observed humidity-dependent friction behavior may be resulted from the formation of capillary water bridges at asperity contacts between the ultrafine-sized amorphous silica grains.

Free Research Field

構造地質学

Academic Significance and Societal Importance of the Research Achievements

岩石の摩擦において，すべり開始前に摩擦面が押しつけられている時間が増加するほど摩擦が大きくなることが知られている．ヒーリングとも呼ばれるこの摩擦強度の時間的増大の性質は，地震時に低下した摩擦の回復過程のみならず，すべり時に摩擦強度が低下する性質を理解する上でも重要である．本研究では人工水晶を用いた実験を行い、断層表面に形成されたナノサイズの摩耗粒子表面に吸着した水が，摩擦の性質に大きく影響していることを明らかにした。