Earthquake fracture damage and feedbacks in the seismic cycle: a multidisciplinary study

地震是一种破坏性很强但又不可预测的地球内部动力的表现形式。它们对应于沿着地质断层的快速运动，当它们沿着断层链传播时会产生地震波。断裂沿断层的传播引起了承载断层的岩石的巨大应力和变形，随着沿断层在地质时间尺度上发生多次地震，这些岩石变得越来越受损(即退化)。反过来，断层外岩石的这种损伤又对动态破裂过程产生影响：损伤产生和地震破裂是耦合现象。因此，更好地了解动态损伤过程可以真正提高我们对地震物理的理解，从而有助于更好地预测强震和地震危害。本研究的目的是研究动态破裂如何在围岩中引起损伤，这种损伤的具体特征，以及它如何影响岩石性质，最终建立一个包括破裂传播和断层外损伤之间的耦合的地震破裂模型。提出的方法是多学科的，包括：(1)对南加州圣哈辛托断层周围自然损坏的样品进行现场表征；(2)在实验室进行非常高变形速率下的岩石变形实验；以及(3)开发一种数值模拟方法，通过对实验数据的测试，可以对完全耦合的地震破裂过程进行模拟。到目前为止，动态损伤研究最具挑战性的方面是在与地震破裂相关的变形速率和压力条件下进行岩石变形实验。为了实现这一目标，我们的建议包括设计和建造一种新的变形装置，该装置将允许对岩石样本进行高速压缩和解压测试。这种装置在欧洲将是独一无二的，将覆盖前所未有的各种变形条件。

Earthquakes are a very destructive and yet unpredictable manifestations of the Earth internal dynamics. They correspond to a rapid motion along geological faults, generating seismic waves as they propagate along the fault strands. The propagation of ruptures along faults induces dramatic stresses and deformation of the rocks hosting the fault, which become increasingly damaged (i.e, degraded) as multiple earthquakes occur along a fault over geological timescales. In turn, this damage of the off-fault rocks has an impact on the dynamic rupture processes: damage generation and earthquake rupture are coupled phenomena. A better knowledge of the dynamic damage processes can thus truly improve our understanding of the physics of earthquakes, and hence help to better predict strong motion and earthquake hazard.It is the goal of this proposal to investigate how dynamic ruptures can induce damage in the surrounding rocks, the specific characteristics of this damage, how it affects the rocks properties, and finally to build an earthquake rupture model which includes the couplings between rupture propagation and off-fault damage. The proposed approach is multidisciplinary, and includes: (1) field characterisation of naturally damaged samples around the San Jacinto fault in South California; (2) laboratory rock deformation experiments at very high deformation rates; and (3) the development of a numerical modeling approach, tested against experimental data, which will allow simulations of fully coupled earthquake rupture processes to be performed.By far the most challenging aspect of the study of dynamic damage is to perform rock deformation experiments at deformation rates and pressure conditions relevant to earthquake ruptures. To achieve this, our proposal includes the design and construction of a novel deformation apparatus which will allow high speed compression and decompression tests to be performed on rock samples. This apparatus will be unique in Europe and will cover an unprecedented range of deformation conditions.