Hydrothermal Friction Experiments on Simulated Basaltic Fault Gouge and Implications for Megathrust Earthquakes
Hydrothermal Friction Experiments on Simulated Basaltic Fault Gouge and Implications for Megathrust Earthquakes
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DOI：
10.1029/2022jb025072
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发表时间：
2022-12
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影响因子：
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通讯作者：
H. Okuda;A. Niemeijer;M. Takahashi;A. Yamaguchi;C. Spiers
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作者：
H. Okuda;A. Niemeijer;M. Takahashi;A. Yamaguchi;C. Spiers
俯冲带中板块边界断层（滑脱）处地震滑动的成核作用与俯冲沉积相的摩擦性质有着广泛的联系。然而，最近的地震学和地质观测表明，至少在某些情况下，在孕震区的深度范围内，俯冲洋壳中会发生滑脱。为了了解海洋地壳物质的摩擦特性及其对地震成因的影响，我们在100-550°C的温度下对蚀变玄武岩的模拟断层泥进行了热液摩擦实验。摩擦系数μ在大多数温度条件下约为0.6，但在最高温度和最低速度条件下观察到低μ至0.3。μ的速度依赖性（a−B）随温度的升高而变化，在100°C时从正变为负，在1450 °C时从负变为正。与来自沉积相的断层泥相比，蚀变玄武岩断层泥在更宽的温度范围内表现出潜在的不稳定速度减弱。显微结构观察和微物理解释推断，通过钠长石的压溶蠕变，增透颗粒流和粘性压实之间的竞争促成了（a-B）中观察到的转变。俯冲过程中洋壳的蚀变通过与间隙水的相互作用产生钠长石和钠长石的细粒，导致其摩擦强度降低，孕震潜力增加。因此，剪切变形可能局限于蚀变洋壳内，导致在孕震带的深度范围内发生大规模逆冲断层地震的可能性更大。
Nucleation of earthquake slip at the plate boundary fault (décollement) in subduction zones has been widely linked to the frictional properties of subducting sedimentary facies. However, recent seismological and geological observations suggest that the décollement develops in the subducting oceanic crust in the depth range of the seismogenic zone, at least in some cases. To understand the frictional properties of oceanic crustal material and their influence on seismogenesis, we performed hydrothermal friction experiments on simulated fault gouges of altered basalt, at temperatures of 100–550°C. The friction coefficient (μ) lies around 0.6 at most temperature conditions but a low μ down to 0.3 was observed at the highest temperature and lowest velocity condition. The velocity dependence of μ, (a−b), changes with increasing temperature from positive to negative at ∼100°C and from negative to positive at ∼450°C. Compared to gouges derived from sedimentary facies, the altered basalt gouge showed potentially unstable velocity weakening over a wider temperature range. Microstructural observations and microphysical interpretation infer that competition between dilatant granular flow and viscous compaction through pressure‐solution creep of albite contributed to the observed transition in (a−b). Alteration of oceanic crust during subduction produces fine grains of albite and chlorite through interactions with interstitial water, leading to reduction in its frictional strength and an increase in its seismogenic potential. Therefore, shear deformation possibly localizes within the altered oceanic crust leading to a larger potential for the nucleation of a megathrust earthquake in the depth range of the seismogenic zone.