Constraints on crustal stress from fault slip data and topography

断层滑动数据和地形对地应力的约束

• 批准号: 1722994
• 负责人: Eric Hetland
• 金额: $ 19.8万
• 依托单位: Regents of the University of Michigan - Ann Arbor
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-11-01 至 2022-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1722994&HistoricalAwards=false
• 关键词: Constraints; crustal; stress; fault; slip; Constraints; crustal; stress; fault; slip

Forces in the Earth's crust lead to ongoing deformation, and in most places, crustal deformation results in destructive earthquakes. Crustal forces and deformation are mathematically represented by stress and strain tensors, respectively. Surface deformation is routinely measured through geodetic techniques and gives insight into the crustal strain field. On the other hand, measuring stress directly is difficult and costly. Hence, the crustal stress field is poorly known compared to strain. In the case of earthquakes, strain around faults that have not recently ruptured indicates the rates that those faults are being loaded, while strain during earthquakes yields information on how the faults slipped at depth. It is crucial to note, however, that earthquakes are inherently stress phenomena, with faults continually loaded until the built-up stress on the faults overcomes their strength. Therefore, while monitoring surface strain provides some information on earthquake potential, insight into seismogenic stresses can advance estimations of earthquake hazard. Over the past several decades, progress has been made in quantifying the orientations of the stresses that led to significant earthquakes; however, quantification of the magnitudes of the stresses that caused those earthquakes has been elusive. In places of high topographic relief, topography itself results in significant stresses on faults. Although, topographic fault stress is only one part of the total stress budget, quantifying it allows the magnitudes of stresses that led to significant earthquakes to be constrained. In addition to an understanding of earthquake processes, this research will contribute to a broader understanding of active tectonics and crustal deformation. In this project, the researcher will constrain the orientations and magnitudes of seismogenic stresses that are consistent with recent moderate to large, continental earthquakes. The researcher seeks to answer three primary questions: 1) What are the magnitudes and orientations of tectonic stress in the crust? 2) How do seismogenic stresses compare to coseismic stress changes? 3) Are topographic stresses correlated to coseismic slip? Answering these questions relies on knowing both the topographic and tectonic stress tensor fields. Topographic stresses are the heterogeneous component of stress that perturb a laterally invariant lithostatic stress in regions of topography. Topographic stresses can be quite heterogeneous across faults, adding shear stresses 10 MPa and normal stresses 50 MPa onto a fault. Correlations between variation of topographic fault stresses and coseismic slip across faults, suggest that the topographic stress field modulates rupture patterns. In this study, a radial basis function, finite difference (RBF-FD) method will be developed to calculate topographic stresses. The RBF-FD method allows for heterogeneous elastic properties and densities, holds for high topographic gradient, and computes stresses throughout the subsurface. The study will use Bayesian methods to estimate the tensorial tectonic stresses that when added to the topographic stresses are consistent with known fault slip. To further constrain stress, focal mechanisms and geologic observations nearby to the earthquakes will be included. The researcher will further analyze the estimated stresses, including investigating correlations between topographic stress and coseismic slip, constraining mechanical fault parameters, and comparing inferred stress in different tectonic regimes. Constraints on seismogenic stresses have the potential to yield substantial insight into issues of earthquake mechanics and active tectonics.

地壳中的力导致持续变形，在大多数地方，地壳变形导致破坏性地震。地壳和变形在数学上分别由应力和应变张量表示。表面变形通常通过大地技术来测量，并深入了解地壳应变场。另一方面，直接测量压力是困难而昂贵的。因此，与菌株相比，地壳应激场是鲜为人知的。在地震的情况下，围绕最近未破裂的断层的应变表明这些断层正在加载的速度，而地震期间的应变产生了有关故障如何在深度下滑的信息。然而，要注意的是，地震是固有的压力现象，断层不断加载，直到对断层的累加压力克服了强度。因此，尽管监测表面应变提供了有关地震潜力的一些信息，但对地震构成应力的洞察力可以提高地震危险的估计。 在过去的几十年中，在量化导致巨大地震的压力方向方面取得了进展。但是，量化引起这些地震的应力的量化是难以捉摸的。在高地形浮雕的地方，地形本身会导致断层的重大压力。虽然，地形断层应力只是总应力预算的一部分，量化它允许将大量的压力大小限制，从而受到限制。除了了解地震过程外，这项研究还将有助于对主动构造和地壳变形的广泛理解。在这个项目中，研究人员将限制与最近至大型大陆地震一致的地震源性应力的方向和幅度。研究人员试图回答三个主要问题：1）地壳中构造压力的幅度和方向是什么？ 2）与coseis震动应力的变化相比，地震施加应力如何？ 3）地形应力是否与coseis震滑相关？回答这些问题依赖于了解地形和构造应力张量场。地形应力是压力的异质组成部分，在地形区域扰动了侧向岩性应力。地形应力在跨断层之间可能是异质的，剪切应力增加了10 MPa，正常应力将50 MPa在断层上增加。地形断层应力的变化与跨断层的coseis震滑之间的相关性，表明地形应力场调节破裂模式。在这项研究中，将开发有限差（RBF-FD）方法来计算地形应力。 RBF-FD方法允许异质弹性特性和密度，可用于高地形梯度，并在整个地下计算应力。该研究将使用贝叶斯方法来估计添加到地形应力时的构造应力，与已知的断层滑动一致。为了进一步限制压力，将包括地震附近的焦点机制和地质观测。研究人员将进一步分析估计的应力，包括研究地形应力与coseisic震动之间的相关性，限制机械断层参数，并比较不同构造方案中推断的应力。对地震应力的限制有可能对地震力学和主动构造问题产生大量见解。