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对深部瞬变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理解。该项目的重点是加利福尼亚州的间歇泉地热田，它是北美最活跃的地震孕育区之一。间歇泉地区是研究时间变化的理想自然实验室，因为间歇泉地区有许多已知的构造和环境引起的应力变化来源。在过去的35年里，抽出蒸汽和注入流体似乎在以前无地震的地区诱发了地震。生产活动会引起地热储的物性变化。与EarthScope InSAR数据一起，来自加州间歇泉密集的本地和区域地震台网的大量高质量连续地震数据为我们提供了构建地下形变源及其时间变异性的详细视图的机会。拟议研究的主要内容是通过观测地震波场中的时间变化来绘制孕震深度的瞬时应力变化图，并附加来自InSAR测量的约束。该项目探索从三分量地震噪声波场推断的地震速度和面波各向异性的时间变化，以表征应力引起的深度裂缝性质(例如裂缝密度和方向)的变化。该项目的另一项活动是研究远程触发地震和地震震动的时空特征。通过集成不同的数据类型，该项目的结果为间歇泉地区的储层特征提供了增强的四维成像。我们正在与劳伦斯·伯克利国家实验室(LBNL)和美国地质调查局合作，实施一个数据采集系统，从LBNL地震台网收集完整的连续地震数据。我们收集的连续地震数据保存在北加州地震数据中心(NCEDC)。所有数据都可通过NCEDC通过互联网向社会提供。

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.