Time-Lapse Monitoring for Detection of Transient Stress Changes in Geysers Geothermal Field

该项目旨在通过将地震发生与改进的地震学和大地测量学对深部瞬时应力变化的观测联系起来，提高我们对地震成核和触发机制的认识。该项目的重点是位于加州的间歇泉地热田，该地热田是北美最活跃的孕震带之一。间歇泉地区是研究时间变化的理想天然实验室，因为间歇泉地区存在许多已知的构造和环境引起的应力变化源。在过去的35年里，蒸汽的抽取和流体的注入似乎在以前的地震区引发了地震。生产活动会引起地热储层的物理变化。与EarthScope干涉合成孔径雷达数据一起，来自加州间歇泉密集的本地和区域地震网络的大量高质量连续地震数据为我们提供了构建地下变形源及其随时间变化的详细视图的机会。 拟议研究的主要组成部分是通过观测地震波场的时间变化绘制孕震深度的瞬时应力变化图，并利用干涉合成孔径雷达测量的其他限制。该项目探讨了从三分量地震噪声波场推断出的地震速度和面波各向异性的时间变化，以表征应力引起的裂缝特性变化（例如，裂纹密度和取向）。该项目的另一项活动是研究远程触发地震和地震震颤的时空特征。通过整合不同的数据类型，该项目的结果提供了间歇泉地区储层特征的增强四维成像。与劳伦斯伯克利国家实验室（LBNL）和美国地质调查局合作，我们正在实施一个数据采集系统，用于从LBNL地震网络收集完整的连续地震数据。我们收集的连续地震数据存档在北方加州地震数据中心（NCEDC）。所有数据都可以通过NCEDC在互联网上向社区提供。

This project aims to improve our understanding of the mechanics of earthquake nucleation and triggering by relating earthquake occurrence to improved seismological and geodetic observations of transient stress changes at depth. The project is focused on the Geysers Geothermal Field in California that is one of the most active seismogenic zones in North America. The Geysers area is an ideal natural laboratory for studying temporal variations is the fact that there are a number of known tectonic and environmentally induced sources of stress change in the Geysers area. Over the past 35 years, it appears that steam withdrawal and fluid injection have induced earthquakes in previously aseismic areas. The production activities would cause physical changes in the geothermal reservoir. Together with EarthScope InSAR data, large volumes of high-quality continuous seismic data from dense local and regional seismic networks at the Geysers, California afford us the opportunity to construct a detailed view of the subsurface deformation sources and their variability in time. The main component of the proposed studies is to map transient stress changes at seismogenic depths through the observation of temporal variations in the seismic wavefield, with additional constraints from InSAR measurements. The project explores temporal variations in seismic velocity and surface-wave anisotropy inferred from the three-component seismic noise wavefield, in order to characterize stress-induced changes in the crack properties (e.g., crack density and orientation) at depth. The other activity of this project examines spatiotemporal characteristics of remotely triggered earthquakes and seismic tremor. By integrating diverse data types, the results from this project provide an enhanced four-dimensional imaging of reservoir characterizations at the Geysers area.In collaboration with Lawrence Berkeley National Laboratory (LBNL) and U.S. Geological Survey, we are implementing a data acquisition system for collecting complete continuous seismic data from the LBNL seismic network. Continuous seismic data that we collect are archived at the Northern California Earthquake Data Center (NCEDC). All data are available to the community over Internet through the NCEDC.