Estimating Frictional Properties of Faults from Geodetic Data

该奖项由2009年美国恢复和再投资法案(公法111-5)资助，产生地震的大型断层表现出广泛的滑动行为，包括导致间歇性地震的粘滑运动，没有快速地震滑动的稳定和稳定滑动，以及没有地震的振荡或非稳定滑动。滑移行为的这一范围可以通过应用摩擦定律来理解和模拟，这些摩擦定律是由天然或合成岩石样品的实验室滑动实验得出的。这些实验获得的摩擦参数被实施在埋藏在地球上的断层的数值模型中，以预测断层的滑动行为。在这些模型中实现的摩擦参数的微小变化可以导致显著不同的滑动行为。例如，参数的微小变化可以从粘滑、地震产生的滑动行为转变为稳定、稳定的无地震滑动行为。因此，了解这些参数在断层上的分布对于地震危险性评估是至关重要的。这项工作的目的是利用S地表在断层附近的运动测量来推断断层上的摩擦参数。旧金山湾区东部的海沃德断层和圣胡安鲍蒂斯塔附近的圣安德烈亚斯断层的测量结果将与断层滑动的数值模型进行比较。这些地点的数据记录了远距离地震引发的断层的瞬时滑动事件。此外，还将系统地检查各种现有的断层蠕变模拟方法，以评估简化假设对模型推断的影响，从而更清楚地了解使用这些方法可以更好地解决断层的摩擦性质。考虑了速率状态摩擦的模型在解释反映断层滑动性质的广泛观测方面非常成功，包括余滑、余震的衰减率、俯冲带的幕式滑动、无声地震以及地震周期的一般特征。引用速率状态摩擦的数值研究使用了实验室得出的摩擦参数，为了简单起见，这些参数通常被假设为只随深度变化。目前尚不清楚实验室摩擦力值与真实断层的相关性有多大。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)Large faults that generate earthquakes exhibit a wide range of slip behaviors including stick-slip motion resulting in episodic earthquakes, stable and steady sliding without fast earthquake slip, and oscillatory or non-steady slip sliding without earthquakes. This range in slip behaviors can be understood and modeled through the application of friction laws derived from laboratory sliding experiments with natural or synthetic rock samples. The friction parameters obtained from these experiments are implemented in numerical models of faults imbedded in the earth in order to predict the slip behavior of faults. Small changes in the friction parameters implemented in these models can lead to dramatically different sliding behaviors. For example, small changes in parameters can change from stick-slip, earthquake producing slip behavior to steady, stable sliding behavior without earthquakes. Knowledge of the distribution of these parameters on faults is therefore essential for earthquake hazard assessment. The object of this work is to use measurements of motions of the Earth?s surface near faults to infer friction parameters on faults. Measurements from the Hayward fault in the eastern San Francisco Bay Area and from the San Andreas fault near San Juan Bautista will be compared with numerical models of fault slip. Data from these locations recorded transient slip episodes on the faults triggered by distant earthquakes. Also, various existing methodologies for modeling fault creep will be systematically examined to assess the influence of simplifying assumptions on model inferences and therefore provider a clearer understanding of how well the frictional properties of faults can be resolved using such approaches.Models incorporating rate-state friction have been remarkably successful in explaining a wide range of observations reflecting the nature of fault slip including afterslip, decay rates of aftershocks, episodic slip at subduction zones, spontaneous silent earthquakes, as well as general features of the earthquake cycle. Numerical studies invoking rate-state friction employ laboratory-derived friction parameters which are often assumed, for simplicity, to vary only with depth. It remains unclear to what extent the laboratory friction values are relevant to real faults.