Experimental and theoretical investigation of rock friction at seismic slip rates

地震滑移率下岩石摩擦的实验和理论研究

• 批准号: 0838255
• 负责人: Kevin Brown
• 金额: $ 22.54万
• 依托单位: University of California-San Diego Scripps Inst of Oceanography
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-09-01 至 2012-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0838255&HistoricalAwards=false
• 关键词: Experimental; theoretical; investigation; rock; friction

The PIs present new experimental data and theory that describe the thermal weakening of fine-grained gouges during earthquake slip. They postulate that the particles in fine-grained gouges thermally soften due to an intrinsic decrease in the elastic shear modulus and increases in plasticity in response to rapid heating of the gouge layer. High-speed weaken processes directly bear on earthquake propagation physics and the origin of the anomalously low state of resolved shear stress on many major plate boundary faults systems, hazardous long run out landslides, and the motion on misaligned faults and low angle detachments. They suppose a simple non-linear weakening model and supporting experimental evidence that explains the principal properties of initial high velocity weakening phase in terms of a thermally controlled increase in the plasticity and decrease in yield strength of the contacting asperities in fault in response to frictional heating. It relies on the well understood concepts of rock plasticity at elevated temperatures and stresses and accounts for the factor observed of 3 to 4 weakening seen in high speed friction tests by considering both the Wachtman-Anderson relationship for the temperature dependent decrease of the elastic modulus and the hyperbolic sine creep law to account for asperity creep at elevated stresses and temperatures. They plan to test the assumption that flash weakening is a truly adiabatic process where the heat caused by the friction is confined to a very thin thermal boundary layer along the asperity contact leaving the bulk of the asperity and attached grains uninvolved in the heating and deformation. The initial data experimental data confirms there is a systematic evolution of the friction coefficient from ~0.5 to as low as 0.15 as velocities increase from 0.14 m/s to 2.5 M/s. However, it does not support the simplified current simple form of the flash-weakening hypothesis. To constrain the theoretical development They will do the following: (1) Obtain thermal record of the average temperatures in the shear zone so we can properly constrain the temperature dependence of the gouge rheology. (2) Examine the shear zone fabrics with a SEM at different velocity and normal stresses to look at the nature of the grain size distribution and evidence for the onset of plastic deformation and melting of gouge particles. (3) Check for the effects of composition (clay vs. crystalline rock) and presence of water on the friction properties. (4) Modify the rotary shear apparatus so that it will run 2 to 4 times slower to extend measurements over a wider velocity range.

PI 提出了新的实验数据和理论，描述了地震滑动过程中细粒凿岩的热弱化。他们假设细粒凿孔中的颗粒由于弹性剪切模量的固有降低而热软化，并且响应于凿孔层的快速加热而塑性增加。高速弱化过程直接影响地震传播物理以及许多主要板块边界断层系统上解析剪切应力异常低状态的起源、危险的长期滑坡以及错位断层和低角度滑脱的运动。他们假设了一个简单的非线性弱化模型和支持实验证据，该证据解释了初始高速弱化阶段的主要特性，即响应于摩擦加热，塑性的热控制增加和断层中接触粗糙体的屈服强度的降低。它依赖于在高温和应力下岩石塑性的众所周知的概念，并通过考虑弹性模量与温度相关的下降的 Wachtman-Anderson 关系，解释了在高速摩擦试验中观察到的 3 至 4 次弱化的因素。双曲正弦蠕变定律可解释在升高的应力和温度下的粗糙蠕变。他们计划测试以下假设：闪光弱化是一个真正的绝热过程，其中摩擦引起的热量被限制在沿着粗糙体接触的非常薄的热边界层中，而使大部分粗糙体和附着的晶粒不参与加热和变形。初始数据实验数据证实，随着速度从 0.14 m/s 增加到 2.5 M/s，摩擦系数会系统性地从 ~0.5 演变到低至 0.15。然而，它不支持闪电减弱假设的简化当前简单形式。为了限制理论发展，他们将做以下工作：（1）获得剪切带平均温度的热记录，以便我们可以适当地限制泥浆流变学的温度依赖性。 (2) 使用 SEM 在不同速度和法向应力下检查剪切区织物，以观察晶粒尺寸分布的性质以及塑性变形和凿孔颗粒熔化开始的证据。 (3) 检查成分（粘土与结晶岩）和水的存在对摩擦性能的影响。 (4) 修改旋转剪切装置，使其运行速度减慢 2 至 4 倍，以在更宽的速度范围内扩展测量。