Remote Triggering Inside Versus Outside Geothermal Fields

自1992年加利福尼亚州发生7.3兆瓦兰德斯地震以来，全球范围内一直在观察和深入研究区域内大地震的远程触发作用。然而，以往的研究大多是在数百公里的空间尺度上进行的，并没有区分人为环境下的实际业务型地热田和自然环境下的相邻断裂带。提议了一个为期两年的项目，详细分析远程触发的地震活动，以检验这样一种假设，即地热场对远程地震的反应与其附近地区不同，这是因为与地热场内部的人为活动有关的应力状态变化。预期的结果将提高人们对孔隙流体压力对地震孕育和相互作用的影响的认识，并有助于建立远程触发和诱发地震活动的模型，这将对评估未来因远程地震和人类活动而在地热领域造成的地震灾害的可能性具有重要意义。在这项拟议的工作中，选择了加州活动构造背景下对应于三次远距离大地震的三个可操作的地热场。研究的重点是比较每个地热场(~10×10 km~2)及其相邻断裂带(~100×100 km~2)的不同行为。结果将解决以下问题：(1)地热场内外的地震活动速率对每一次远程地震的响应是如何变化的？(2)地热场内外的应力场有何不同？(3)浅层地震和深部地震对远程触发有何响应？(4)地热场内的净生产率与地震活动率之间是否存在相关性？(5)地热场内外的地震速度结构和现场波速比有什么不同？

Remote triggering by large earthquakes at regional distances has been globally observed and intensely studied since the 1992 Mw 7.3 Landers earthquake in California. However, most of the previous studies were conducted at spatial scales of hundreds of kilometers and did not differentiate the actual operational geothermal fields with anthropogenic setting and their adjacent fault zones with natural setting. A two-year project is proposed for detailed analyses of the remotely triggered seismicity to examine hypothesis that geothermal fields respond differently from their vicinity to remote earthquakes due to the stress-state changes that are associated with the anthropogenic activity inside the geothermal field. The expected results will improve knowledge of the effect of pore fluid pressure on earthquake initiation and interaction and contribute to models of remotely triggered and induced seismicity, which will be important for evaluating the potential of future seismic hazards in geothermal fields due to remote earthquakes and human activity. In this proposed work, three operational geothermal fields under active tectonic settings in California corresponding to three large distant earthquakes are selected. The focus of this research is to compare different behaviors between each geothermal field (~10x10 km^2) and their adjacent fault zones (~100x100 km^2) that are split into several subareas. The results will address the following questions: (1) How does seismicity rate change inside and outside the geothermal fields responding to each remote earthquake? (2) How different are the stress fields inside and outside the geothermal fields? (3) How do shallow and deep earthquakes respond to remote triggering? (4) Is there any correlation between the net production rate and the seismicity rate inside the geothermal field? (5) What is the difference in the seismic velocity structure and in situ Vp/Vs inside and outside the geothermal fields?