Theoretical earthquake nucleation, with applications to creep fronts, tremor, and slow slip

摘要该奖项由2009年美国复苏和再投资法案资助（公法111 -5）。传统上，断层被认为以两种方式之一来适应滑动：粘滑运动，其中断层基本上被锁定的长时期被短暂的快速滑动打断（地震），以及板块构造速率下的稳定蠕变（厘米/年）或更少。过去十年中，在许多俯冲带内发现了幕式缓慢滑动和相关震颤，和地震沿着圣安德烈亚斯断层，表明断层的行为是更加多样的。在幕式慢滑中，断层的滑动速率比板块构造速率大1至2个数量级，其准规则间隔约为1年。由于滑动事件持续数周，并延伸到数十至数百公里的区域，它们释放的能量相当于6级或更高的地震。震颤是一种准连续的地震信号，被认为是由无数的小事件组成的，类似于1.5级或更小的常规地震，只是更加缓慢。由于缓慢滑动事件增加了在9级地震中可能发生滑动的断层的浅锁部分的应力速率，因此了解它们可能对减少地震灾害有用。此外，从这项工作中产生的对滑动局部化的更多理解可以用来解释正在进行的监测加州和南非几公里深处地震成核的实验。在过去的几年里，PI与Jean-Paul Ampuero一起工作，以了解变形断层上地震成核的标准速率和状态摩擦方程的含义。他们推导出的解析解对于理解复杂的数值模拟非常有用。本文将这一工作扩展到俯冲带和圣安德烈亚斯断层沿着的慢滑动和震颤的解释，并将数值和解析技术相结合，逐渐形成一种共识，即慢滑动和震颤只是非均匀界面上滑动的不同表现。蠕动锋的平行性似乎是慢滑动非均匀断层的普遍特征，并且在它们碰撞时产生地震滑动速度是非常有效的。本研究的第一个目标是要解决多远，这种蠕变战线可能会传播隔离，和必要的条件，两个碰撞的前锋，以产生地震滑动。这将进行两个标准率andstatesfriction和其他本构关系，已提出了慢滑。一旦蠕变锋碰撞，他们可以产生地震事件的时刻率的历史，这取决于潜在的本构律，是完全不同的，从那些地震学家已经开始期待。辐射阻尼近似弹性动力学和最终完全弹性动力学。由于目前许多信息来自潮汐和地震触发的震颤的观测，这两种形式的触发将被建模。

ABSTRACTThis award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law111-5).Traditionally, faults were thought to accommodate slip in one of two ways: Stick-slip motion,in which long periods where the fault is essentially locked are punctuated by brief episodes ofrapid slip (earthquakes), and steady creep at plate tectonic rates (centimeters per year) or less. Thediscoveries within the last decade of episodic slow slip and associated tremor within numeroussubduction zones, and tremor along the San Andreas fault, show that fault behavior is much morevaried. In episodic slow slip, faults slip at rates 1 to 2 orders of magnitude larger than plate tectonicrates at quasi-regular intervals on the order of 1 year. Because the slip episodes last for severalweeks and extend over areas tens to hundreds of kilometers across, they release energy equivalentto earthquakes of magnitude 6 or more. Tremor is a quasi-continuous seismic signal thought tobe made up of myriad small events similar to regular earthquakes of magnitude 1.5 or less exceptin being more sluggish. Because slow slip events increase the stressing rate on the shallowerlocked portion of faults that can slip in magnitude 9 earthquakes, understanding them may proveto be useful for earthquake hazards reduction. In addition, the increased understanding of sliplocalization that arises from this work can be used to interpret ongoing experiments monitoringearthquake nucleation at several kilometers depth in California and South Africa.Over the past several years the PI has worked with Jean-Paul Ampuero to understand the implicationsof the standard rate-and-state friction equations for earthquake nucleation on deformablefaults. They derived analytic solutions that have been very useful for understanding complex numericalsimulations. This proposal is to extend this work to the interpretation of slow slip andtremor in subduction zones and along the San Andreas fault, using both numerical and analyticaltechniques.A consensus is emerging that slow slip and tremor are just different manifestations of slip ona heterogeneous interface. Propagating creep fronts seem to be a ubiquitous feature of slow slipon heterogeneous faults, and are very effective at generating seismic slip speeds when they collide.Both properties make creep fronts attractive as tremor sources. The first goal of this study is toaddress how far such creep fronts might propagate in isolation, and the necessary conditions fortwo colliding fronts to generate seismic slip. This will be carried out both for standard rate-andstatefriction and for other constitutive laws that have been proposed for slow slip. Once the creepfronts collide, they can generate seismic events with moment rate histories that, depending upon theunderlying constitutive law, are quite different from those that seismologists have come to expect.This will be studied initially using the ?radiation damping? approximation to elastodynamics andultimately full elastodynamics. Because much information is currently coming from observationsof tidally- and teleseismically-triggered tremor, both forms of triggering will be modeled.