Using small events to constrain the physical mechanism governing slow slip

在传统的模型中，断层可能以两种方式之一滑动：稳定地以接近板块速度的速度滑动，或者在地震中以间歇性滑动。然而，在过去的二十年里，研究人员发现了另一种行为：慢滑事件。在慢滑动事件中，大部分板块界面滑动周期性地加速，但在达到地震滑移率之前很久就停止了。令人困惑的是为什么：是什么物理机制允许发生缓慢但间歇性的滑动？理解间歇性的慢滑很重要，因为慢滑事件发生在锁定带的正下方，那里是危险的巨型逆冲地震的发源地。对慢滑的约束可以帮助我们约束地震发育区如何加载到破坏。慢滑甚至可能帮助我们理解大地震是如何开始的，因为控制慢滑开始的物理很可能是支配大地震开始的相同的物理。慢滑也很重要，因为它是丰富的。在大多数仪器齐全的俯冲带上观察到了M&GT；6事件，容纳了深部板块界面滑动的大部分。如果我们要了解地震旋回和俯冲区的应力状态，我们就需要了解慢滑。人们已经提出了许多解释慢滑的物理机制。其中一些模型再现了缓慢但幕式滑动，通常是通过考虑断层流变学的复杂性或断层性质的空间变化。然而，这些模型似乎并不能再现观察到的慢滑事件的所有性质。具体地说，这些模型被设计成缓慢且相对稳定的，因此它们很难再现在慢滑事件中越来越多地被观察到的复杂性。因此，我们似乎需要一个新的或修改过的模式。挑战在于，有许多看似合理的模式可供考虑。因此，在这个项目中，我建议评估几个模型，并确定几个模型属性，这些属性对于再现观察到的慢滑是必不可少的。为了更好地评估这些模型，我建议将它们与现有的大型慢滑事件的观测结果进行比较，以及对卡斯卡迪亚中部更多小型慢滑事件的新数据进行分析。卡斯卡迪亚每年发生数十次小的慢滑事件。它们伴随着地震震动：低幅度、持续的地震振动，被认为是由慢滑事件驱动的无数微小地震组成的。我们将跟踪地震的位置，这样我们就可以看到小的慢滑事件是如何在太空中生长的。此外，我们将利用卡斯卡迪亚独特的高精度PBO钻孔应变仪网络，估计小地震中的无地震滑动强度。我们将使用这些新的分析来评估几个慢滑的数值模型，并约束基本的模型特征。

In conventional models, faults can slip in one of two ways: steadily at rates near plate rate or episodically in earthquakes. However, in the past two decades researchers have discovered another behaviour: slow slip events. In slow slip events, large portions of the plate interface slip accelerate periodically but then stall long before reaching seismic slip rates. The puzzle is why: what physical mechanism allows for slow yet episodic slip?Episodic slow slip is important to understand because slow slip events occur just below the locked zone, which hosts hazardous megathrust earthquakes. Constraints on slow slip can help us constrain how the earthquake-generating region is loaded to failure. Slow slip may even help us understand how large earthquakes start, as the physics governing the beginning of slow slip is likely the same physics that governs the beginning of large earthquakes.Slow slip is also important because it is abundant. M>6 events have been observed on most well-instrumented subduction zones, accommodating large fractions of the plate interface slip at depth. If we are to understand the seismic cycle and the stress state at subduction ones, we need to understand slow slip.A number of physical mechanisms have been proposed to explain slow slip. And a number of these models have reproduced the slow yet episodic slip, usually by allowing for complications in the fault rheology or spatial variations in the fault properties. However, these models have not appeared capable of reproducing all the properties of observed slow slip events. Specifically, the models are designed to be slow and relatively stable, so they struggle to reproduce the complexity that is increasingly observed within a slow slip event. It thus seems that we need a new or modified model. The challenge is that there are many plausible models to consider. So in this project, I propose to evaluate several models and to identify several model properties that are essential to reproducing observed slow slip. To better evaluate these models, I propose to compare them with existing observations of large slow slip events as well as new analysis of data from the more numerous small slow slip events in central Cascadia. Several tens of small slow slip events occur annually in Cascadia. They are accompanied by seismic tremor: low-amplitude, sustained seismic vibrations thought to be composed of numerous tiny earthquakes driven by the slow slip event. We will track the tremor locations, so that we can see how the small slow slip events grow in space. In addition, we will estimate the magnitude of aseismic slip in the small events, using the unique network of high-precision PBO borehole strainmeters in Cascadia. We will use these new analyses to evaluate several numerical models of slow slip and constrain essential model characteristics.