Abstract Regarding the occurrence of seismicity on major plate-boundary fault zones, one leading hypothesis is that the processes of lithification is responsible transforming loose, unconsolidated sediment that does not host earthquake nucleation into the frictionally unstable rocks that inhabit the seismogenic zone. Previous laboratory studies comparing the frictional properties of intact rocks and powdered versions of the same rocks generally support this hypothesis. However, systematically quantifying frictional behavior as a function of lithification remains a challenge. Here, we simulate the lithification process in the laboratory by consolidating mixtures of halite and shale powders with halite-saturated brine, which we then desiccate. The desiccation allows precipitation of halite as cement, creating synthetic rocks. We quantify lithification by: (1) direct measurement of cohesion, and (2) measuring the porosity reduction of lithified samples compared to powders. We observe that powdered samples of each halite-shale proportion exhibit predominantly velocity-strengthening friction, whereas lithified samples exhibit a combination of velocity strengthening and significant velocity weakening when halite constitutes at least 30 wt% of the sample. Analysis of the individual rate-dependent friction parameters shows that the occurrence of velocity weakening is due to relatively low values of a for lithified samples. Larger velocity weakening is associated with cohesion of >∼1 MPa, and porosity reduction of >∼50 vol%. Microstructural images reveal that the shear surfaces for powders tend to exhibit small cracks not seen on the lithified sample shear surfaces. Our results suggest that lithification via cementation and porosity loss can facilitate slip instability, supporting the lithification hypothesis for seismogenic slip.

中文翻译：

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实验室控制的石化作用引起的速度减弱摩擦

摘要 关于在主要板块边界断层带上发生地震活动，一个主要假设是岩石化过程负责将没有地震成核的松散、松散的沉积物转化为栖息在发震带的摩擦不稳定岩石。以前的实验室研究比较了完整岩石和相同岩石的粉末版本的摩擦特性，通常支持这一假设。然而，系统地量化作为石化函数的摩擦行为仍然是一个挑战。在这里，我们通过将岩盐和页岩粉末与岩盐饱和盐水的混合物固结在实验室中模拟岩化过程，然后将其干燥。干燥使岩盐以水泥形式沉淀，形成合成岩石。我们通过以下方式量化锂化：（1）内聚力的直接测量，以及（2）与粉末相比，测量锂化样品的孔隙率减少。我们观察到每个岩盐-页岩比例的粉末样品主要表现出速度强化摩擦，而当岩盐占样品的至少 30 wt% 时，岩化样品表现出速度强化和显着速度减弱的组合。对各个速率相关摩擦参数的分析表明，速度减弱的发生是由于岩化样品的 a 值相对较低。较大的速度减弱与大于 1 MPa 的内聚力和大于 50 vol% 的孔隙率降低有关。微观结构图像显示，粉末的剪切表面往往会出现在锂化样品剪切表面上看不到的小裂纹。