Contemporary Cascadia Deformation overDisparate Time Scales: Systematics of Slow Earthquakes and Fore-arc Impingement

利用全球定位系统(GPS)的连续观测可以高精度地确定水平和垂直形变率及其在时间和空间上的变化。本项目主要研究太平洋西北部卡斯卡迪亚会聚边缘目前由GPS确定的四维形变场的两个方面。首先，正在调查卡斯卡迪亚巨型逆冲带上瞬变事件的时空分布。这一部分研究的动机是，根据对Panga网络的分析，初步结果表明，自1992年以来，太平洋西北部至少发生了8次Mw 6.0(当量)的无声地震(持续数天至数月的无震滑动事件)。使用主成分分析对数据进行重新分析，其结果用于空间反演，以确定每个蠕变事件在板界面上的弯矩屈服、空间位置和迁移。其次，迁移的大陆前弧(华盛顿州西部)遇到刚性扶壁(温哥华岛)时的运动学正在通过分析Panga阵列的速度场、建立卡斯卡迪亚边缘和Puget Lowland板内变形的断层几何学和力学块体模型来研究。

Continuous observations using Global Positioning System (GPS) geodesy yield high-precision determination of horizontal and vertical deformation rates and their variation in time and space. This project focuses on two aspects of the current GPS-determined four-dimensional deformation field along the Cascadia convergent margin in the Pacific Northwest. First, the spatial and temporal distribution of transient events on the Cascadia megathrust is being investigated. This part of the study is motivated by preliminary results that indicate at least 8 silent earthquakes (aseismic slip events lasting days to months) with Mw 6.0 (equivalent) occurred in the Pacific Northwest since 1992 based on analysis of the PANGA network. The data are being reanalyzed using principal component analysis the results of which are used for spatial inversion to determine the moment yield, spatial locations, and migration of each creep event across the plate interface. Second, the kinematics of the migrating continental fore-arc (western Washington) as it encounters a rigid buttress (Vancouver Island) are being examined by analysis of the velocity field from the PANGA array, and development of fault geometry and mechanical block models of the intraplate deformation of the Cascadia margin and Puget Lowlands.