Collaborative Research: High-resolution imaging of the Elgin-Lugoff earthquake swarm sequence and subsurface structures in South Carolina using a dense seismic nodal array

合作研究：使用密集地震节点阵列对南卡罗来纳州埃尔金-卢戈夫地震群序列和地下结构进行高分辨率成像

• 批准号: 2321095
• 负责人: Daniel Frost
• 金额: $ 16.84万
• 依托单位: University of South Carolina at Columbia
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-08-01 至 2025-07-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2321095&HistoricalAwards=false
• 关键词: Collaborative; Research; resolution; imaging; Elgin

A prolonged earthquake swarm sequence started on December 27, 2021, beginning with a magnitude 3.3 earthquake between Elgin and Lugoff in South Carolina, a region with very low prior seismic activity. More than 90 small earthquakes have been reported in this region since then, with the largest magnitude of 3.6 occurring on June 29, 2022. These earthquakes have continued until at least summer of 2023, making this highly unusual for the region. This swarm has had no clear main shock and has no obvious tectonic or anthropogenic causes. So far, standard earthquake locations do not reveal a clear relationship with the pre-existing Eastern Piedmont Fault System. This project will analyze seismic data from a set of instruments deployed by the researchers in October 2022 to better image the fault structure hosting the swarm and the underlying driving force. This project will naturally provide opportunities for public engagement with the impacted community in Elgin-Lugoff, and the broader midlands of South Carolina, where many residents have felt earthquakes for the first time in their lives. This project also provides inclusion and STEM workforce development opportunities, by funding research by undergraduate students from the local South Carolina community to perform research in their own state. Students on this grant will participate in outreach to build STEM literacy through knowledge transfer and further broaden participation in geoscience. This project will also provide funding to support summer internships at both institutions.In October 2022, 85 seismic nodes were deployed for 4 months by the research team over the Elgin-Lugoff swarm to record further earthquakes. These instruments were complemented by one broadband station and one nearby strong motion station operated by the South Carolina Seismic Network. The rich dataset can be used to identify additional smaller earthquakes, which will better image fault structures hosting this swarm sequence and elucidate the driving forces. The work will attempt to reveal small earthquakes during the nodal deployment period, below the detection threshold before this deployment, by using both machine learning and template matching techniques. The team will then relocate these newly detected events with waveform-based techniques, followed by focal mechanism determinations. This information will be used to construct a new model of the seismic velocities beneath Elgin. Using both the more complete catalog and the improved velocity model, the earthquakes earlier in this swarm can be relocated relative to the later ones thus improving the accuracy of the whole catalogue. Results from this project will answer the following questions: 1) does the swarm occur in a diffuse or well-defined region, 2) how the swarm evolved in space and time, and 3) what is the likely process that drives this swarm. The information gained from the analysis will inform on the ongoing tectonic processes in South Carolina, and on East coast seismicity and tectonics generally.This project is jointly funded by the Geophysics program and the Established Program to Stimulate Competitive Research (EPSCoR).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.

2021年12月27日，一个长时间的地震群序列开始，首先是南卡罗来纳州的埃尔金和卢格夫之间发生的3.3级地震，该地区之前的地震活动非常低。自那时以来，该地区报告了90多次小地震，最大震级为3.6级，发生在2022年6月29日。这些地震至少持续到2023年夏天，这对该地区来说是极不寻常的。这个震群没有明显的主震，也没有明显的构造或人为原因。到目前为止，标准的地震位置并没有揭示出与先前存在的东部皮埃蒙特断层系统的明确关系。该项目将分析研究人员于2022年10月部署的一套仪器的地震数据，以更好地成像承载群的断层结构和潜在的驱动力。该项目自然将为埃尔金-卢格夫和南卡罗来纳州更广泛的中部地区的受影响社区提供公众参与的机会，那里的许多居民一生中第一次感受到地震。该项目还提供包容性和STEM劳动力发展机会，资助来自当地南卡罗来纳州社区的本科生在自己的州进行研究。该补助金的学生将参与外展活动，通过知识转移建立STEM素养，并进一步扩大对地球科学的参与。2022年10月，研究团队在埃尔金-卢格夫震群上部署了85个地震节点，为期4个月，以记录更多的地震。这些仪器由南卡罗来纳州地震网络运营的一个宽带台站和附近的一个强震动台站补充。丰富的数据集可用于识别其他较小的地震，这将更好地对承载该群序列的断层结构进行成像，并阐明驱动力。这项工作将尝试通过使用机器学习和模板匹配技术，在节点部署期间，在部署之前低于检测阈值的情况下揭示小地震。然后，该团队将使用基于波形的技术重新定位这些新检测到的事件，然后确定震源机制。这一信息将被用来构建一个新的模型的地震速度下埃尔金。利用更完整的目录和改进的速度模型，可以重新定位该群中较早的地震相对于较晚的地震，从而提高整个目录的准确性。这个项目的结果将回答以下问题：1）蜂群是否发生在一个扩散或定义明确的区域，2）蜂群如何在空间和时间上进化，3）驱动这个蜂群的可能过程是什么。从分析中获得的信息将为南卡罗来纳州正在进行的构造过程以及东海岸的地震活动和构造提供信息。该项目由地球物理计划和刺激竞争性研究的既定计划（EPSCoR）共同资助。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。