Collaborative Research: Dynamic fault rupture in the presence of 3D heterogenous tectonic stress: the case of the San Andreas Fault in Eastern San Gorgonio Pass

合作研究：三维异质构造应力存在下的动态断层破裂：以圣戈戈尼奥山口东部圣安德烈亚斯断层为例

• 批准号: 1623739
• 负责人: David Oglesby
• 金额: $ 16.45万
• 依托单位: University of California-Riverside
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-08-01 至 2019-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1623739&HistoricalAwards=false
• 关键词: Collaborative; Research; Dynamic; fault; rupture

The San Andreas Fault is the largest and arguably the most dangerous source of earthquakes in Southern California. It has produced very large (magnitude greater than 7.5) earthquakes in the past, and it is likely to do so again, with essentially no warning. One of the key tools that seismologists can use to help anticipate and mitigate the effects of such future disasters is to make numerical (computer) models of potential earthquakes. Current numerical models indicate that an earthquake that propagates from Indio toward Los Angeles, through the San Gorgonio Pass (SGP), can channel ground shaking energy directly toward the Los Angeles Basin, where it is amplified by basin sediments and can lead to very high ground motion. Thus, it is extremely important to determine whether such an earthquake that passes through the SGP is likely (or even possible). This is not a trivial question, as the fault structure in the San Gorgonio Pass is quite complex, with the main San Andreas splitting into a number of smaller faults with different orientations and directions of slip. We will use the most accurate available modeling techniques to address the question of whether an earthquake can propagate through this region, leading to a large, damaging event for the region. We will focus on the eastern SGP, where the Coachella Valley strand of the SAF branches into the Mission Creek, Banning, and Garnet Hill fault strands. Each of these strands has very different structure and apparent activity levels, so an understanding of through-going earthquake potential in the region may hinge on whether there is a preferred rupture path in this region. This project implements numerical models of potential earthquakes in this region to determine which of these strands is the most likely path of an earthquake. The models use fault stresses derived from long-term simulations of fault slip and Earth surface deformation in the region, and give information on potential earthquake rupture path, slip distribution, earthquake size, and ground motion. These innovative earthquake models will also include the effects of rock failure away from the faults, which may have a significant effect on the energy budget of earthquakes. This work constitutes an important advance in the science of earthquake modeling, and it has important broader impacts, including estimates of earthquake size and ground motion in the region, with further implications for engineering, zoning, and emergency response. The question of whether an earthquake can propagate through the San Gorgonio Pass (SGP) region of the San Andreas Fault (SAF) is of tremendous scientific and societal importance. The SGP is a ?pinch point? along this fault system, in which the SAF splits into multiple non-coplanar segments, including both strike-slip and thrust; there may well be no through-going surface to support continuous earthquake rupture in this region [e.g., Yule, 2009]. Numerical models [e.g., Olsen et al., 2008] indicate that an earthquake rupture that propagates through the SGP from southeast to northwest can channel seismic radiation directly toward the Los Angeles Basin, where it is amplified by basin sediments and can lead to very high ground motion. Thus, the question of whether the San Gorgonio Pass serves as a significant barrier to earthquake rupture propagation is of great practical as well as theoretical interest, and it affects ground motion not just locally but in the most populated regions of Southern California. This work aims to help answer this question by performing numerical models of potential earthquakes in this region. Specifically, we will focus on the eastern SGP, where the Coachella Valley segment of the SAF branches into the Mission Creek, Banning, and Garnet Hill fault strands. Each of these strands has very different structure and apparent activity levels, so an understanding of through-going earthquake potential in the region may hinge on whether there is a preferred rupture path in this region. We will use a combination of methods to address this question: coupled long-term and interseismic quasi-static modeling method to determine the on- and off-fault stresses in the region, and a 3D dynamic rupture model that uses these stresses to model potential earthquakes, including rupture propagation, slip, and near-source ground motion. Each of these methods has been well tested individually, but this is the first time that they have been combined in this way. The work will is a significant advance in the field of realistic fault dynamics, in that it is (to the PIs knowledge) the first study to combine a tectonically- and geometrically-consistent heterogeneous stress field with off-fault failure; prior models have had either but not both of these abilities. Earlier homogenous-stress models that incorporate such failure mechanisms [Andrews, 2005; DeDontney et al., 2012; Duan and Day, 2008; Dunham et al., 2011; Gabriel et al., 2013] indicate that off-fault plasticity can have a very strong effect on the energy budget and rupture propagation during an earthquake; we expect the inclusion of these effects in our heterogeneous stress models to be at least as significant. Our work will advance the science of fault dynamics in regions of geometrical complexity, especially fault branches. The methods developed in this project are readily applicable to other earthquake-prone regions with significant fault complexity, such as Northern California. The results have important implications for earthquake occurrence in the SGP, as well as for seismic hazard throughout Southern California. In particular, it has important implications for estimates of potential earthquake size in Southern California, and consequently the generation of strong ground motion and estimation of seismic hazard. This information can be useful for engineering, zoning, and emergency response purposes. In addition, the investigators perform outreach activities to the local Morongo Band Of Mission Indians in San Gorgonio Pass. This funding supports the Ph.D. research of a talented young postdoctoral researcher of Afro-Caribbean ancestry, a significantly under-represented group within the Geosciences.

圣安德烈亚斯的断层是南加州最大的，可以说是最危险的地震来源。 过去，它曾产生非常大的（大于7.5）的地震，并且很可能再次这样做，基本上没有警告。 地震学家可以用来帮助预测和减轻这种未来灾难的影响的关键工具之一是制造潜在地震的数值（计算机）模型。 当前的数值模型表明，通过San Gorgonio Pass（SGP）传播从Indio到洛杉矶的地震可以将地面摇动向洛杉矶盆地引导，并通过盆地沉积物扩大，并可以导致非常高的地面运动。 因此，确定通过SGP的地震是否可能（甚至可能），这是非常重要的。 这不是一个微不足道的问题，因为San Gorgonio Pass中的故障结构非常复杂，主要的San Andreas分为许多较小的断层，具有不同的方向和滑动方向。我们将使用最准确的可用建模技术来解决地震是否可以通过该地区传播的问题，从而导致该地区发生的大型破坏性事件。 我们将重点关注东方SGP，SAF分支的Coachella Valley链进入Mission Creek，Baning和Garnet Hill的断层链。 这些链中的每一个都有非常不同的结构和明显的活性水平，因此了解该地区的整个地震潜力可能取决于该地区是否有首选破裂路径。 该项目实现了该地区潜在地震的数值模型，以确定这些链中的哪一个是地震最有可能的路径。 模型使用该区域中断层滑动和地面表面变形的长期模拟得出的断层应力，并提供有关潜在地震破裂路径，滑动分布，地震大小和地面运动的信息。 这些创新的地震模型还将包括岩石故障远离断层的影响，这可能会对地震的能量预算产生重大影响。 这项工作构成了地震建模科学的重要进步，并且具有更广泛的影响，包括对该地区地震规模和地面运动的估计，对工程，分区和应急响应产生了进一步的影响。地震是否可以通过圣安德烈亚斯断层（SAF）的San Gorgonio Pass（SGP）地区传播的问题具有巨大的科学和社会重要性。 SGP是“捏点”？沿着这种断层系统，其中SAF将其分为多个非跨层段，包括滑滑和推力；很可能没有遍地的表面来支持该地区的连续地震破裂[例如，Yule，2009]。 数值模型[ 因此，圣戈戈尼奥通行证是否是地震破裂传播的重要障碍的问题，既实用又具有理论利益，并且不仅在当地，而且在南加州人口最多的地区都会影响地面运动。 这项工作旨在通过在该地区进行潜在地震的数值模型来帮助回答这个问题。 具体来说，我们将重点关注东部SGP，SAF分支的Coachella Valley段进入Mission Creek，Banning和Garnet Hill的断层链。 这些链中的每一个都有非常不同的结构和明显的活性水平，因此了解该地区的整个地震潜力可能取决于该地区是否有首选破裂路径。 我们将使用方法的组合来解决这个问题：长期和微观的准准静态建模方法耦合，以确定该地区的内部和异化应力，以及一个3D动态破裂模型，该模型使用这些压力来模拟潜在的地震，包括破裂，滑移，滑移和接近选择的地面运动。 这些方法中的每一种都经过了单独测试，但这是它们第一次以这种方式组合。 这项工作将是现实断层动态领域的重大进步，这是（就PIS知识而言）是第一个将构造和几何矛盾的异质应力场与损坏失败相结合的研究。先前的模型具有这些能力，但不是两种能力。 早期结合了这种失败机制的同质压力模型[Andrews，2005; Dedontney等人，2012年； Duan and Day，2008年； Dunham等，2011； Gabriel等人，2013年]指出，在地震期间的能量预算和破裂繁殖可能会产生非常强烈的影响；我们期望将这些效应纳入我们的异质应力模型中至少具有重要意义。我们的工作将推进几何复杂性区域（尤其是断层分支）区域中断层动力学的科学。该项目中开发的方法很容易适用于其他具有明显断层复杂性的易于地震的地区，例如北加州。结果对SGP的地震发生以及整个加利福尼亚州的地震危害具有重要意义。特别是，它对南加州的潜在地震规模的估计具有重要意义，因此产生了强大的地面运动和地震危险的估计。 此信息对于工程，分区和应急响应目的可能很有用。此外，调查人员还向圣戈尔贡尼奥帕斯（San Gorgonio Pass）的当地莫朗戈（Morongo）印第安人摩根哥乐队（Morongo Band）进行外展活动。 这项资金支持博士学位。对非洲加勒比血统的一位才华横溢的年轻博士后研究员的研究，这是一个地球科学中代表性不足的群体。