Capturing and comparing slow slip events in Cascadia and New Zealand using a novel, physics-based approach

在过去的15-20年里，全球定位系统技术彻底改变了我们跟踪地球仪周围构造板块边界变形率的时空变化的能力。 通常，这些数据是从以下方面进行分析的：（a）时间平均场地速度;（B）离散位移;（c）位移率的时间变化;或（d）将全球定位系统速度转换成应变率。值得注意的是，在世界各地的板块边界连续运行的GPS仪器导致了？慢滑事件？这是一种以前未知的断层滑动形式，涉及以稳定的板块边界位移和产生地震所需的滑动速度之间的中间速率跨越断层的瞬时地震滑动（持续数周至数月）。 为了突破GPS可以获得的变形过程的空间和时间分辨率的极限，该项目将采用我们团队最近开发的一种新的基于物理学的方法，使用连续GPS（cGPS）数据客观地检测和表征慢滑事件，其时空分辨率高于使用现有方法。与传统方法不同，我们的新方法（首次）从cGPS时间序列中获得水平应力垂直导数（VDoHS）。VDoHS速率是与这些（和其他）变形事件相关联的地下力的最紧密解析的表面表达。我们将实施我们的新方法来表征和检测卡斯卡迪亚俯冲带（太平洋西北部）和Hikurangi俯冲边缘（新西兰）的慢滑事件（SSE），这两个区域都被密集的连续GPS网络覆盖。此外，由于Hikurangi和Cascadia的SSE的持续时间和震级特征存在很大差异，该项目将使我们能够使用新方法研究宽范围的慢滑事件类型。在全球范围内对俯冲带板块边界的SSE和相关地震现象的观测引发了当今地震学研究中最具活力的领域之一。为了促进对SSE过程的全面理解，我们的新方法将（a）降低大地测量可检测SSE的阈值，增加我们对SSE滑动行为的全谱的知识;（B）能够客观、高分辨率地识别SSE，并揭示其与巨型逆冲断层锁定的时间变化的关系，和（c）促进Hikurangi和Cascadia SSE及其与地震活动和震颤的关系的详细比较。我们还预计，我们的方法的适应cGPS时间序列分析瞬态变形将铺平道路，一个急需的方法，将cGPS数据与时间相关的地震危险性模型。

Over the last 15-20 years, GPS technology has revolutionized our ability to track spatial and temporal variations in rates of deformation at tectonic plate boundaries around the globe. Typically, these data are analysed in terms of (a) time-averaged site velocities; (b) discrete displacements; (c) temporal variations in displacement rates, or (d) converting GPS velocities into strain rates. Notably, continuously operating GPS instruments at plate boundaries around the world have led to the discovery of ?slow slip events?, which are a previously unknown form of fault slip that involves transient aseismic slip across a fault (lasting weeks to months) at a rate intermediate between steady plate boundary displacement and the slip velocity required to generate earthquakes. To push the boundaries on the limits of spatial and temporal resolution of deformation processes that can be obtained by GPS, this project will adapt a novel, physics-based approach that our team has recently developed to use continuous GPS (cGPS) data to objectively detect and characterize slow slip events at a higher spatio-temporal resolution than can be done using existing methods. Unlike conventional methods, our new approach (for the first time) obtains Vertical Derivatives of Horizontal Stress (VDoHS) rates from cGPS timeseries. VDoHS rates are the most tightly resolved surface expression of subsurface forces associated with these (and other) deformation events. We will implement our new method to characterize and detect slow slip events (SSEs) at the Cascadia subduction zone (Pacific Northwest) and the Hikurangi subduction margin (New Zealand), both of which are well-covered by dense continuous GPS networks. Moreover, due to the strong differences in the duration and magnitude characteristics of SSEs at Hikurangi and Cascadia, this project will allow us to investigate a broad spectrum of slow slip event types using the new method.The observation of SSEs and associated seismic phenomena at subduction zone plate boundaries worldwide has ignited one of the most dynamic fields of research in seismology today. To advance the overall understanding of SSE processes, our new method will (a) lower the threshold of geodetically detectable SSEs, increasing our knowledge of the full spectrum of SSE slip behavior; (b) enable objective, high resolution identification of SSEs, and reveal the relationship of this to temporal variations in megathrust locking, and (c) foster a detailed comparison of Hikurangi and Cascadia SSEs and their relationship to seismicity and tremor. We also expect that the adaptation of our method to cGPS timeseries to analyse transient deformation will pave the way for a much needed approach to incorporating cGPS data into time-dependent seismic hazard models.