INsights into rupture DIrectivity patterns from microseismicity to weak events: implications on induced seismicity by fluid injection processes (INDI)

了解自然地震和诱发地震的成核和破裂增长过程对于评估和减轻对人和基础设施的相应时间依赖性危害非常重要。先进的震源分析，包括点源模型，但也有限源反演，提供信息的破裂几何形状，破裂大小，破裂速度，滑动幅度和配置的主要滑动补丁在地震破裂。此外，破裂的方向性，描述了一个潜在的不对称性破裂传播是最相关的方面出现从这样的反演。了解是什么控制了主要的破裂方向，是预测大地震破裂过程如何演变、最终破裂规模以及后果的关键。该项目的主要目标是评估驱动成核和增长的地震源的物理过程，由流体注入操作刺激，以了解是什么控制破裂前传播的方向。特别是，该项目旨在了解为什么观察到单向或双向破裂模式，以及为什么地震破裂主要沿沿着某个方向传播，讨论与地震前应力条件有关的有限源反演结果。从技术上讲，该研究提案旨在开发在不同空间和震级尺度上进行扩展断层反演和破裂方向性的有效工具，旨在提供有关诱发地震活动的震源特性的详细和可靠信息。我们将区分和调查与不同震级尺度的断裂和断层复活过程相关的诱发地震活动案例：i）与废水处理活动相关的最大诱发地震（例如，俄克拉荷马州地震）; ii）在专门的近场网络中记录的震级小于零的声发射（AE）事件，用于在瑞典的艾斯珀硬岩实验室进行的水力压裂实验。总之，该项目旨在通过以下方式扩展当前的最新技术水平：1）在从中/大诱发地震到水力裂缝的不同尺度上稳健地解决点和有限源参数（破裂持续时间，破裂方向性和破裂大小）。2)了解人为操作和应力扰动是否控制破裂方向性和扩展，从而控制地震震级。3)在诱发地震和自然地震之间架起桥梁：诱发地震发生在触发因素和应力历史更为熟知的环境中，可用于了解构造地震的破裂成核和传播。

Understanding the process of nucleation and rupture growth of natural and induced earthquakes is important for the assessment and mitigation of the corresponding time-dependent hazards to people and infrastructure. Advanced seismic source analysis, including point source models but also finite source inversions, provide information on rupture geometry, rupture size, rupture velocity, slip amplitude and the configuration of main slip patches in an earthquake rupture. In addition, rupture directivity, describing a potential asymmetry in rupture propagation is one of the most relevant aspects to emerge from such inversions. Understanding what controls the dominant rupture direction is key to forecast how the rupture process of large earthquakes may evolve, their final rupture size and thus their consequences. The main target of this project is to assess the physical processes which drive nucleation and growth of seismic sources, stimulated by fluid injection operations, in order to understand what controls the direction the rupture front propagates. In particular, the project aims to understand why uni- or bilateral rupture modes are observed and why earthquake ruptures propagate dominantly along a certain direction, discussing finite source inversion results in relation to the pre-seismic stress conditions. Technically, the research proposal aims to develop efficient tools for extended fault inversion and rupture directivity at different spatial and magnitude scales, aiming to provide detailed and robust information about the seismic source properties of induced seismicity. We will discriminate and investigate cases of induced seismicity related to fracturing and fault reactivation processes at different magnitude scales: i) the largest induced earthquakes related to wastewater disposal activities (e.g Oklahoma earthquakes); ii) acoustic emission (AE) events with magnitude less than zero recorded in a dedicated near field network for hydraulic fracturing experiments that took place in the Äspö Hard Rock Laboratory (Sweden). In summary, this project aims to extend the current state-of-the-art by: 1) Resolve robustly point and finite source parameters (rupture duration, rupture directivity and rupture size) on different scales from moderate/large induced earthquakes to hydraulic fractures. 2) Understand whether human operations and stress perturbation control the rupture directivity and growth, and thus the earthquake magnitude. 3) Bridge the link between induced and natural seismicity: induced seismicity, occurring in environments where triggering factors and stress histories are better known, can be used to learn about rupture nucleation and propagation for tectonic earthquakes.