The Spectrum of Fault Slip Behaviors and the Mechanics of Slow Earthquakes

地震代表了储存在构造断层附近岩石中的弹性能量的突然释放，导致了灾难性的破坏。在正常（快速）地震中，破裂带以每秒几公里的速度扩张，断层滑动率达到每秒1到10米。然而，构造断层也会在持续数月或更长时间的缓慢地震中破裂，断层滑动速度为每秒不到一英寸的几分之一。最近的研究表明，构造断层在包括缓慢地震、正常（快速）地震和许多其他形式的滑动模式的频谱中失败。这些缓慢的滑动模式可以将应力转移到快速地震区，并可能引发破坏性的正常地震。然而，我们对慢震的机制知之甚少。这项研究将解决如下问题：是什么决定了慢震的破裂速度？这项工作的一个核心要素是通过连续测量声发射、弹性波速度和振幅以及断裂带摩擦行为，仔细进行重复、缓慢粘滑事件的实验室研究。需要测试的假设包括：1)慢滑破坏是否代表一系列材料的正常（快速）滑动过早停止，2)同一断裂带是否可以承载慢滑和快速滑动行为。慢震是瞬态断层滑动的一种形式，它可能给断裂带的发震部分带来载荷，并引发破坏性地震。慢震的起源和瞬变断层滑动的相关形式尚不清楚。该项目将采取系统的方法来调查：1)慢滑的潜在过程，重点研究摩擦机制和连续介质耦合，这可能解释断层滑动行为的频谱；2)实验室样品的微观结构研究，以评估正常（快）和慢粘滑之间剪切局部化和应变分布的比较；3)断层带弹性特性的声学测量，特别关注破坏的前兆。拟议的研究将扩展摩擦粘滑和正常（快）地震之间的类比，以包括慢滑事件。这些结果将为慢震和其他形式的准动态断层滑动的机制提供见解。获得的所有数据和结果将发表在同行评议的期刊上，并通过公共网站提供。

Earthquakes represent a sudden release of elastic energy that is stored in the rocks adjacent to tectonic faults, driving catastrophic failure. In normal (fast) earthquakes the rupture zone expands at a few kilometers per second, and fault slip rates reach 1 to 10 meters per second. However, tectonic faults also fail in slow earthquakes with rupture durations of months or more and fault slip speeds of a of small fraction of an inch per second or less. Recent work shows that tectonic faults fail in spectrum of slip modes that includes slow earthquakes, normal (fast) earthquake, and many other forms of slip. These slow modes of slip can transfer stress to the fast earthquake zone and potentially trigger damaging, normal earthquakes. However, we know very little about the mechanics of slow earthquakes. This research effort will address questions such as: what determines the rupture speed of slow earthquakes? A central element of this work is carefully conducted laboratory studies of repetitive, slow stick-slip events with continuous measurement of acoustic emission, elastic wave speed and amplitude, and fault zone friction behavior. Hypotheses to be tested include: 1) does slow slip failure represents prematurely arrested normal (fast) slip for a range of materials and 2) can the same fault zone can host slow and fast slip behaviors.Slow earthquakes are one form of transient fault slip that may load seismogenic portions of fault zones and abet damaging earthquakes. The origin of slow earthquakes and related forms of transient fault slip is poorly understood. The project will take a systematic approach to investigate: 1) the underlying processes of slow slip, with focus on the frictional mechanisms and continuum coupling that may explain the spectrum of fault slip behaviors in nature, 2) microstructural studies of the laboratory samples to assess how shear localization and strain distribution compare between normal (fast) and slow stick-slip, and 3) acoustic measurement of fault zone elastic properties, with particular focus on precursors to failure. The proposed study will extend the analogy between frictional stick-slip and normal (fast) earthquakes to include slow slip events. The results will provide insight on the mechanics of slow earthquakes and other forms of quasi-dynamic fault slip. All data and results obtained will be published in peer-reviewed journals and made available via public websites.