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

该项目旨在通过将利用实验室导出的速率和状态摩擦定律的后滑模型与大地震后变形的大地测量记录进行比较，进一步了解断层摩擦特性的分布。断层耦合的理想化观点涉及地震中破裂的地震间锁定部分，以及锁定区上方和下方的抗震蠕动部分，这与许多板块边界断层的观测结果不一致。例如，圣安德烈亚斯断层被锁定在加州帕克菲尔德以南约15公里深处，但在帕克菲尔德以北，圣安德烈亚斯断层在典型的孕震深度蠕动。1999年台湾集集地震和2003年日本十胜冲地震的运动学滑动反演显示，在典型的孕震深度，沿主震走向沿着有显著的余震。本研究利用这两次地震及2004年加州帕克菲尔德地震的GPS资料，探讨断层的滑动与摩擦性质的分布。实施实验室导出的速率状态摩擦法的后滑数值模型正在开发和实施的地震后GPS时间序列数据的摩擦参数反演。在孕震深度的非滑动观测提出了关于断层摩擦特性和滑动行为沿走向变化的重要问题。一般认为地壳孕震部分的断层是稳态速度减弱。然而，速度减弱摩擦并不总是导致不稳定的滑动和速度增强摩擦并不总是导致稳定的滑动。本研究调查的条件下，允许在滑动行为的空间变化的故障。在帕克菲尔德和十胜冲地震后以1赫兹记录的高速率GPS数据正被用于调查地震期间从动态滑动到地震后稳定蠕变的转变。从不稳定的过渡的性质可以提供对断层上的摩擦性质的进一步约束。

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.