Detailed seismic imaging and monitoring of the subsurface material around the San Jacinto fault zone

这项研究开发和使用了先进的地震学技术和由加州南部圣哈辛托断裂带(SJFZ)周围空间密集的断裂带阵列记录的连续波形数据。对这些数据的分析提供了浅层地壳的地震速度和衰减系数的详细特征(可能与时间有关)。为了为新技术提供基准并了解地震性质如何随位置和深度变化，调查人员使用了安装在断裂带内和邻近断裂带的浅井地震仪记录的数据，以及区域地震台网的记录。这些结果补充了通常不能解决浅地壳地震性质的层析研究模型，并允许开发基本上直到地表的SJFZ周围的地震结构模型。浅层地壳的地震性质知识与观测到的地面运动和破坏过程特别相关。这些结果可能与许多其他应用有关，包括地壳水文学、地热能、地下水库和储存，以及基础设施的地震安全。本研究开发的分析方法可用于其他地区地下材料的抗震性能研究。这项研究使用最先进的数据和新的地震成像和监测技术来缩小关键的观测差距。这些研究涉及以下关键问题：(1)SJFZ不同地段和断层外场地地壳顶部几百米处的地震速度和衰减系数是什么？(2)浅层岩石在什么应力/应变幅度下具有与不同加载机制和周期(例如，本地和远程地震、潮汐和季节变化)和位置有关的非线性响应和性质的时间变化，与断裂带、场地条件参数、和深度？(3)不同载荷产生的地震性质和恢复时间尺度的时间变化幅度如何与断裂带、场地条件和深度有关？(4)是否有更容易发生故障的断裂段和/或断层外地点(表现为与时间相关的地震性质)，如果发现了它们，能否确定这些地区的异常性质，以解释敏感性升高？这些研究可以大大增强地壳顶部几百米处地震速度和衰减系数、非线性响应和性质的时间变化的可用现场表征。预计这些结果将提供基本信息，可能有助于更好地了解地震地面运动(因此震动危险)以及其他应用。

This study develops and uses advanced seismological techniques and continuous waveform data recorded by spatially-dense fault zone arrays around the San Jacinto Fault Zone (SJFZ) in southern California. Analyses of these data provide detailed characterization of (potentially time-dependent) seismic velocities and attenuation coefficients of the shallow crust. To provide benchmarks for the new techniques and understand how seismic properties change with location and depth, the investigators use data recorded by shallow borehole seismometers installed within and adjacent to the fault zone, as well as recordings from regional seismic networks. These results complement models of tomographic studies that typically do not resolve seismic properties in the shallow crust, and allow development of seismic structural models around the SJFZ essentially up to the surface. Knowledge of seismic properties of the shallow crust is particularly relevant to observed ground motion and failure processes. These results may be relevant to numerous other applications including crustal hydrology, geothermal energy, subsurface reservoirs and storage, as well as seismic safety of infrastructure facilities. The analysis methods develop by this research can be used in studies of seismic properties of the subsurface material in other locations. The research uses state-of-the-art data and novel seismic imaging and monitoring techniques to close critical observational gaps. The studies address the following key questions: (1) What are the seismic velocities and attenuation coefficients in the top few hundred meters of the crust at various sections of the SJFZ and at sites that are off the fault? (2) At what stress/strain amplitudes do shallow rocks have nonlinear response and temporal changes of properties in relation to different loading mechanisms and periods (e.g., local and remote earthquakes, tides, and seasonal variations) and location with respect to the fault zone, site condition parameters, and depth? (3) How do amplitudes of temporal changes of seismic properties and recovery timescales produced by various loadings vary in relation to the fault zone, site conditions and depth? (4) Are there fault sections and/or off-fault sites with higher susceptibly to failures (manifested by time-dependent seismic properties), and if they are found, can anomalous properties in these regions be identified that may explain the elevated susceptibility? The studies can augment significantly the available in situ characterization of seismic velocity and attenuation coefficients, nonlinear response and temporal changes of properties in the top few hundred meters of the crust. The results are expected to provide fundamental information that may lead to improved understanding of seismic ground motion (and hence shaking hazard) as well as other applications.