How Deep Do Ruptures Penetrate in Large Earthquakes?

大地震中破裂的深度有多深？

• 批准号: 0911221
• 负责人: Bruce Shaw
• 金额: $ 16.46万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-08-01 至 2011-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0911221&HistoricalAwards=false
• 关键词: How; Deep; Do; Ruptures; Penetrate

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Technical Description:In the shallow crust, most of the strain at plate boundaries is relieved during sudden rare large earthquakes. Below the shallow locked portion, strain has often been thought as being relieved through steady creep, or, in the case of layers just below the locked portions, slow decaying afterslip. In the last few years, observations of Episodic Tremor and Slip in subduction zones has caused some rethinking of this simple picture. An even bigger challenge to this picture has come from new theoretical work suggesting rapid coseismic slip during large earthquakes might penetrate much deeper below the locked fault than previously thought. This possibility, that rapid coseismic deep slip may have been, not missed, but rather misplaced, inferred erroneously to be happening at shallower locked depths, has significant implications for our picture of how strain relief occurs at plate boundaries, and for seismic hazard estimates. This work seeks to further explore and constrain this possibility.Two sets of projects are proposed. The first set focuses on a newly identified quantification of the deep slip behavior found to have significant impacts on seismic hazard estimates: the ratio of seismogenic moment to total moment (or seismogenic moment fraction). This ratio is argued to impact magnitude-area scaling, moment balanced estimates of repeat times of large events, and high frequency shaking hazard. Further re-examing the implications of this ratio, and constraining its values forms a core of this set of projects. Examining this ratio in a forward modeling context to capture its robustness to friction and other uncertainties is a central proposed project. Specifically, variations in friction in the seismogenic layer, and frictional forms in the deeper stably sliding layer will be examined, and robustness of this dimensionless ratio explored. Additional projects studying the seismogenic moment fraction and its impact on quantities relevant to seismic hazard will be carried out. In particular, we will examine how well the estimated seismogenic moment fraction corrections indeed match magnitude area scaling and large event repeat times.The second set of projects focuses on measurements which have the potential to provide direct observational constraints of the phenomena of deep slip below the locked portion of faults. Taking advantage of the geometry of dipping faults, where depth and horizontal location are associated, one project will examine the potential to detect deep slip at the surface in dipping fault geometries. In the case of subduction zones, the project aims to see whether slip propagation into zones where Episodic Tremor and Slip occur might be observable during large earthquakes. A final project examines magnitude-area scaling on dipping faults, in light of our new scaling laws.Broader Significance: In addition to the broad areas of earth science touched by this research, including geological, seismological, geodetic, and laboratory observations, there are significant potential practical benefits to society. Current methods for estimating seismic hazard rely on a series of of parameterizations of ruptures to construct probabilities of earthquake occurrence. Uncertainties in the parameterizations lead to uncertainties in the estimates, and added uncertainties mean added costs, when trying to manage risk. It has become increasingly clear that a more physics-based approach would provide better constraints on parameterizations and better hazard estimates. This work hasimportant implications for a number of key parameterizations used in seismic hazard estimates. These seismic hazard estimates have big societal impacts, and are used for setting building codes and earthquake insurance rates. Improving estimates help in better allocating resources to mitigate these hazards, ultimately saving lives and property.

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。技术描述：在地壳浅层，板块边界的大部分应变在罕见的大地震中被解除。在浅锁定部分以下，应变通常被认为是通过稳定的蠕变，或者，在锁定部分以下的岩层中，是缓慢衰减的余震。在过去的几年里，对俯冲带的间歇性震颤和滑动的观察引起了对这一简单图景的一些重新思考。对这一观点更大的挑战来自新的理论研究，该研究表明，大地震期间的快速同震滑动可能比之前认为的更深入锁定断层下方。这种可能性，即快速的同震深滑动可能没有被遗漏，而是错位了，错误地推断发生在较浅的锁定深度，这对我们关于板块边界应变释放如何发生的图景和地震危险性估计具有重要意义。这项工作旨在进一步探索和限制这种可能性。提出了两套方案。第一组侧重于新确定的对地震危险性估计有重大影响的深滑动行为的量化：发震力矩与总力矩的比率（或发震力矩分数）。这一比例被认为会影响震级面积尺度、大事件重复次数的矩平衡估计和高频震动危险。进一步重新审视这一比例的含义，并限制其价值，形成了这组项目的核心。在正模拟环境中检查这一比率，以捕获其对摩擦和其他不确定性的鲁棒性是一个中心提出的项目。具体地说，将研究发震层中的摩擦变化，以及更深层稳定滑动层中的摩擦形式，并探讨这种无量纲比率的鲁棒性。将开展其他项目，研究孕震力矩分数及其对地震危险性相关量的影响。特别是，我们将研究估计的孕震力矩分数校正与震级面积尺度和大事件重复次数的匹配程度。第二组项目侧重于有可能对断层锁定部分以下的深滑动现象提供直接观测约束的测量。利用倾斜断层的几何形状，其中深度和水平位置相关联，一个项目将检查在倾斜断层几何形状中探测地表深滑动的潜力。在俯冲带的情况下，该项目旨在观察在大地震期间是否可以观察到滑动传播到间歇性震颤和滑动发生的区域。最后一个项目检查了倾斜断层的震级面积缩放，根据我们的新缩放定律。更广泛的意义：除了本研究涉及的广泛的地球科学领域，包括地质学、地震学、大地测量学和实验室观测外，还有对社会的重大潜在实际效益。目前估计地震危险性的方法依赖于一系列的破裂参数化来构造地震发生的概率。当试图管理风险时，参数化中的不确定性会导致评估中的不确定性，而增加的不确定性意味着增加的成本。越来越清楚的是，更基于物理的方法将对参数化提供更好的约束和更好的危害估计。这项工作对地震灾害估计中使用的一些关键参数化具有重要意义。这些地震风险评估具有巨大的社会影响，并用于制定建筑规范和地震保险费率。改进估算有助于更好地分配资源以减轻这些危害，最终挽救生命和财产。