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推导的速率和状态摩擦定律的余震模型与大地测量记录的大地震后变形进行比较，进一步了解断层上摩擦特性的分布。断层耦合的理想观点涉及地震中破裂的地震间锁断段，以及锁断带上下的地震蠕动段，这与许多板块边界断层的观察结果不一致。例如，圣安德烈亚斯断层被锁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易震深度蠕动。1999年台湾集集地震和2003年日本德立树地震的运动学滑动反转显示，在主震走向的典型发震深度有明显的余震。本研究利用这两次地震和2004年加州帕克菲尔德地震的GPS数据来研究断层上滑动和摩擦特性的分布。执行实验室推导的速率状态摩擦规律的余震数值模型正在开发中，并用于反演地震后GPS时间序列数据的摩擦参数。地震发震深度的地震滑动观测提出了断层上的摩擦特性和滑动行为沿走向变化的重要问题。地壳发震区内的断层通常被假定为稳态速度减弱。然而，速度减弱摩擦并不总是导致不稳定滑移，速度增强摩擦也并不总是导致稳定滑移。本研究探讨了断层上允许滑动行为空间变化的条件。Parkfield和Tokachi-oki地震后记录的1hz高速率GPS数据被用于研究地震期间从动态滑动到地震后稳定蠕变的转变。从不稳定过渡的性质可能对断层的摩擦特性提供进一步的约束。

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.