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，GPS技术彻底改变了我们追踪全球构造板块边界变形速率的时空变化的能力。通常，根据(A)时间平均场地速度；(B)离散位移；(C)位移速率的时间变化；或(D)将GPS速度转换为应变率来分析这些数据。值得注意的是，在世界各地的板块边界上持续运行的GPS仪器导致了“慢滑事件”的发现，这是一种以前未知的断层滑动形式，涉及跨断层的瞬时无地震滑动(持续数周至数月)，其速率介于稳定的板块边界位移和引发地震所需的滑动速度之间。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，这个项目将采用我们团队最近开发的一种新的基于物理的方法，使用连续GPS(CGPS)数据以比使用现有方法更高的时空分辨率客观地探测和描述慢滑事件。与传统方法不同，我们的新方法(首次)从CGPS时间序列获得水平应力垂直导数(VDoHS)率。VDoHS速率是与这些(和其他)变形事件相关的次表面力的最紧密解析表面力表达式。我们将实施我们的新方法来表征和探测卡斯卡迪亚俯冲带(太平洋西北)和希库兰吉俯冲边缘(新西兰)的慢滑事件(SSE)，这两个地区都被密集的连续GPS网很好地覆盖。此外，由于Hikurangi和Cascadia的SSE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广泛的慢滑事件类型。在世界各地俯冲带板块边界观察到SSE及其相关地震现象，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)降低从大地测量可检测到的SSE的门槛，增加我们对SSE滑动行为全谱的了解；(B)能够客观、高分辨率地识别SSE，并揭示其与巨型逆冲锁定的时间变化的关系；以及(C)促进Hikurangi和Cascadia SSE的详细比较及其与地震活动和地震的关系。我们还预计，我们的方法适用于CGPS时间序列来分析瞬时形变，将为将CGPS数据纳入随时间变化的地震风险模型铺平道路。

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.