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

本研究开发并使用先进的地震学技术和连续波形数据记录的空间密集断层带阵列周围的圣哈辛托断层带（SJFZ）在南加州。对这些数据的分析提供了浅地壳地震速度和衰减系数（可能与时间有关）的详细特征。为了为新技术提供基准，并了解地震特性如何随位置和深度而变化，调查人员使用了安装在断层带内和附近的浅井地震仪记录的数据，以及区域地震网络的记录。这些结果补充了层析成像研究的模型，这些模型通常不能解决地壳浅层的地震特性，并允许开发SJFZ周围的地震结构模型，基本上达到地表。浅部地壳地震特性的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。本研究所发展的分析方法可用于其它地区地下介质地震特性的研究。该研究使用最先进的数据和新颖的地震成像和监测技术来填补关键的观测空白。这些研究解决了以下关键问题：（1）在SJFZ的各个部分和在远离断层的地点，地壳顶部几百米处的地震速度和衰减系数是什么？(2)在什么应力/应变幅下，浅层岩石具有与不同加载机制和周期相关的非线性响应和性质的时间变化（例如，本地和远程地震，潮汐和季节变化）和位置相对于断层带，现场条件参数，和深度？(3)地震性质的时间变化幅度和由各种载荷产生的恢复时间尺度如何随断层带、场地条件和深度而变化？(4)是否存在故障敏感性较高的断层段和/或断层外场地（表现为随时间变化的地震属性），如果发现了这些区域，是否可以识别出这些区域的异常属性，从而解释敏感性升高的原因？这些研究可以大大增加现有的地震速度和衰减系数，非线性响应和地壳顶部几百米的属性的时间变化的现场表征。预计结果将提供基础信息，可能会导致地震地面运动（因此震动危害）以及其他应用程序的更好的理解。

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.