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Oceanic transform fault seismicity and slip mode influenced by seawater infiltration
Nature Geoscience ( IF 18.3 ) Pub Date : 2021-08-05 , DOI: 10.1038/s41561-021-00778-1
Arjun Kohli 1 , Monica Wolfson-Schwehr 2 , Cécile Prigent 3 , Jessica M. Warren 4
Affiliation  

Oceanic transform faults that offset mid-ocean ridges slip through earthquakes and aseismic creep. The mode of slip varies with depth and along strike, with some fault patches that rupture in large, quasi-periodic earthquakes at temperatures <600 °C, and others that slip through creep and microearthquakes at temperatures up to 1,000 °C. Rocks from both fast- and slow-slipping transforms show evidence of interactions with seawater up to temperatures of at least 900 °C. Here we present a model for the mechanical structure of oceanic transform faults based on fault thermal structure and the impacts of hydration and metamorphic reactions on mantle rheology. Deep fluid circulation is accounted for in a modified friction-effective pressure law and in ductile flow laws for olivine and serpentine. Combined with observations of grain size reduction and hydrous mineralogy from high-strain mylonites, our model shows that brittle and ductile deformation can occur over a broad temperature range, 300–1,000 °C. The ability of seawater to penetrate faults determines whether slip is accommodated at depth by seismic asperities or by aseismic creep in weak, hydrous shear zones. Our results suggest that seawater infiltration into ocean transform faults controls the extent of seismicity and spatiotemporal variations in the mode of slip.



中文翻译:

海水入渗影响的大洋转换断层地震活动和滑动模式

抵消大洋中脊的大洋转换断层在地震和抗震蠕变中滑动。滑动模式随深度和沿走向而变化,一些断层带在温度 <600 °C 的大型准周期性地震中破裂,而其他断层带则在高达 1,000 °C 的温度下通过蠕变和微地震滑动。来自快速和慢速滑动转变的岩石显示出与海水相互作用的证据,温度至少达到 900 °C。在这里,我们提出了一个基于断层热结构以及水化和变质反应对地幔流变学影响的大洋转换断层力学结构模型。深层流体循环在改进的摩擦有效压力定律和橄榄石和蛇纹石的延性流动定律中得到了解释。结合对高应变糜棱岩的晶粒尺寸减小和含水矿物学的观察,我们的模型表明,脆性和韧性变形可以在 300-1,000°C 的宽温度范围内发生。海水穿透断层的能力决定了滑动是由地震凹凸体在深度还是由弱含水剪切带的地震蠕变来调节的。我们的研究结果表明,海水渗入海洋转换断层控制着地震活动的程度和滑动模式的时空变化。

更新日期:2021-08-05
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