Towards the Understanding of Deep Crustal Faulting and Fluid Movement through the Analysis of Long Period Earthquakes at Clearlake, CA

通过分析加利福尼亚州克利尔莱克的长期地震来了解深部地壳断层和流体运动

• 批准号: 2051759
• 负责人: Douglas Dreger
• 金额: $ 13.9万
• 依托单位: University of California-Berkeley
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-05-01 至 2024-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2051759&HistoricalAwards=false
• 关键词: Towards; Understanding; Deep; Crustal; Faulting

Volcanos pose serious threats to human societies yet can be sources of geothermal energy. Clear Lake Volcanic Field is a volcanic steam field located in California. It hosts numerous geothermal power plants. Although it has not erupted for 11,000 years, it exhibits volcanic-type seismic activity such as tremors and long-period (LP) events. LP events are produced by fluids surging through cracks and faults in the Earth’s crust. Studying these events allows better understanding fluid movement and fault dynamics. This is important economically and to better assess seismic and volcanic hazards. However, seismic signals from LP events are small and challenging to detect and analyze. Here the researchers investigate these events at Clear Lake Volcanic Field. They use seismology which is the study of seismic waves generated by earthquakes and travelling through the Earth. The waves are detected at the surface and analyzed. The researchers leverage on existing data. They combine state-of-the-art analytical techniques to better identify and locate the LP events. They examine the dynamic properties of the events (stress drops), their scaling with magnitude, and when possible the focal mechanisms of the earthquakes that produced them. The improved catalog of LP events, high-resolution locations, and focal mechanisms is used to investigate the fluid transport system in the region. The project outcomes – which include refined methods and development of hybrid approaches to improve LP event analysis – could be applied at other volcanic systems. The one-year project also supports a collaboration between academia and the industry, and educational outreach to the public. The study is based on existing catalog of seismic waveform data that have shown to include LP events. These events are compared to non-volcanic tremor and low-frequency earthquakes at other places along the San Andreas fault system. The researchers search the continuous waveform data set using adaptive waveform template matching to identify LP events related to events already in the catalog. They develop new templates - based on waveform similarity - to further interrogate the data and detect and catalog new LP events. They use the double-difference location method to develop a high-resolution catalog. The detected events are analyzed using spectral modeling methods to estimate the scalar seismic moment and corner frequency; the goal is to assess possible scaling properties of the LP earthquakes. The team also utilizes three-component waveform data to determine focal parameters from moment tensor inversion. LP events are small and challenging to model and therefore require efforts toward the refinement of methods and the development of hybrid approaches to extract more reliable results. Because of their small magnitude, the researchers need to explore combined inversion scheme that utilizes a source-type inversion of both waveforms and first-motion polarities, possibly expanding the method to utilize body wave amplitude ratios. The results of the multipronged analysis will be used to investigate potential fault structure and the fluid transport system of the Clear Lake Volcanic Field. It will also allow evaluating whether continued study is warranted with a possible portable array deployment to improve coverage to better investigate LP earthquake seismicity.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

火山对人类社会构成严重威胁，但可以成为地热能源的来源。清澈的湖水火山田是一个火山蒸汽田位于加州。 它拥有许多地热发电厂。虽然它已经有11，000年没有喷发了，但它表现出火山型的地震活动，如地震和长周期（LP）事件。 LP事件是由地壳中的裂缝和断层中涌动的流体产生的。研究这些事件可以更好地理解流体运动和断层动力学。这在经济上很重要，也有助于更好地评估地震和火山灾害。然而，来自LP事件的地震信号很小，并且检测和分析具有挑战性。在这里，研究人员调查这些事件在清澈的湖水火山场。 他们使用地震学，这是研究地震产生的地震波，并通过地球旅行。 波在表面被检测并被分析。 研究人员利用现有数据。它们结合了联合收割机最先进的分析技术，以更好地识别和定位LP事件。他们检查事件的动态特性（应力下降），它们与震级的比例，以及可能时产生它们的地震的震源机制。LP事件，高分辨率的位置和震源机制的改进目录被用来调查该地区的流体输送系统。项目成果-包括改进方法和开发混合方法以改进LP事件分析-可应用于其他火山系统。这个为期一年的项目还支持学术界和工业界之间的合作，以及对公众的教育宣传。这项研究是基于现有的地震波形数据目录，已显示包括LP事件。这些事件相比，非火山震颤和低频率地震在其他地方沿着圣安德烈亚斯断层系统。研究人员使用自适应波形模板匹配搜索连续波形数据集，以识别与目录中已有事件相关的LP事件。他们基于波形相似性开发新的模板，以进一步询问数据并检测和编目新的LP事件。他们使用双差定位法来开发高分辨率的星表。检测到的事件进行了分析，使用频谱建模方法来估计标量地震矩和拐角频率，其目标是评估可能的LP地震的标度特性。该团队还利用三分量波形数据来确定矩张量反演的焦点参数。LP事件很小，建模具有挑战性，因此需要努力改进方法和开发混合方法，以提取更可靠的结果。由于它们的震级很小，研究人员需要探索联合反演方案，该方案利用波形和第一运动极性的源型反演，可能将该方法扩展到利用体波振幅比。多管齐下的分析结果将用于调查潜在的断层结构和清澈的湖水火山区的流体输送系统。 它还将允许评估是否有必要通过可能的便携式阵列部署来继续研究，以提高覆盖范围，从而更好地调查LP地震地震活动性。该奖项反映了NSF的法定使命，并且通过使用基金会的知识价值和更广泛的评估被认为值得支持影响审查标准。