Collaborative Research: Utilizing GPS Measurements of Postseismic Deformation to Infer Spatial Distribution of Frictional Properties on Faults

这个项目试图通过将利用实验室得出的速率和状态摩擦定律的余滑模型与大地震后的大地形变记录进行比较，来加深我们对断层上摩擦特性分布的理解。断层耦合的理想化观点涉及地震中破裂的地震间闭锁区段，在锁闭区带的上方和下方都有非地震爬行区段，这与从一些板块边界断层上观察到的情况不一致。例如，圣安德烈亚斯断层锁定在加利福尼亚州帕克菲尔德以南约15公里深的地方，但在帕克菲尔德以北，圣安德烈亚斯断层正在典型的地震孕育深度爬行。1999年台湾集集地震和2003年日本东京地震的运动滑移反演表明，在典型的孕震深度，沿着主震的走向，存在显著的余滑。这项研究利用这两次地震和2004年加州帕克菲尔德地震的GPS数据来调查断层上滑动和摩擦性质的分布。正在开发实施实验室导出的速率-状态摩擦定律的余滑数值模型，并在地震后GPS时间序列数据的摩擦参数反演中实施。孕震深度的无震滑动观测提出了断层上的摩擦性质和滑动行为的沿走向变化的重要问题。地壳孕震部分的断层通常被认为是稳态速度减弱的。然而，速度减弱摩擦并不总是导致不稳定滑动，速度增强摩擦并不总是导致稳定滑动。这项研究调查了断层上允许滑动行为空间变化的条件。Parkfield和Tokachi-oki地震后以1赫兹记录的高速GPS数据正被用来研究地震期间动态滑动到地震后稳定蠕变的转变。从不稳定转变的性质可能会对断层上的摩擦性质提供进一步的限制。

This project is seeking to further our understanding of the distribution of frictional properties on faults by comparing afterslip models utilizing laboratory-derived rate and state friction laws with geodetic records of deformation following large earthquakes. The idealized view of fault coupling involving an interseismically locked section that ruptures in earthquakes, with aseismically creeping sections above and below the locked zone, is inconsistent with observations from a number of plate boundary faults. For example, the San Andreas fault is locked above about 15 km depth south of Parkfield, California, but north of Parkfield, the San Andreas is creeping at typically seismogenic depths. Kinematic slip inversions from the 1999 Chi-Chi, Taiwan earthquake and the 2003 Tokachi-oki, Japan earthquake show significant afterslip at typically seismogenic depths, along strike from the mainshocks. This research utilizes GPS data from these two earthquakes and the 2004 Parkfield, California earthquake to investigate the distribution of slip and frictional properties on faults. Numerical models of afterslip implementing laboratory derived rate-state friction laws are being developed and implemented in inversions of postseismic GPS time-series data for frictional parameters. The observations of aseismic slip at seismogenic depths raise important questions about frictional properties on the fault and along-strike variations of slip behavior. Faults within the seismogenic part of the crust are generally assumed to be steady-state velocity weakening. Yet, velocity weakening friction does not always lead to unstable slip and and velocity strengthening friction does not always lead to stable slip. This study investigates the conditions on the fault that allow for the spatial variations in slip behavior. High-rate GPS data recorded at 1 Hz following the Parkfield and Tokachi-oki earthquakes is being used to investigate the transition from dynamic slip during the earthquake to stable creep following the earthquake. The nature of the transition from unstable may provide further constraints on the frictional properties on the fault.