RAPID: Seismic Deployment for Capturing Aftershocks of the September 2017 Chiapas (M=8.1) and Puebla (M=7.1) Mexico Earthquakes

RAPID：用于捕获 2017 年 9 月墨西哥恰帕斯州 (M=8.1) 和普埃布拉 (M=7.1) 地震余震的地震部署

• 批准号: 1764426
• 负责人: Aaron Velasco
• 金额: $ 3.47万
• 依托单位: University of Texas at El Paso
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-11-01 至 2018-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1764426&HistoricalAwards=false
• 关键词: RAPID; Seismic; Deployment; Capturing; Aftershocks

The September 7 Chiapas, Mexico (M=8.1) and the September 19 Puebla, Mexico (M=7.1) earthquakes occurred along a subduction zone, where the oceanic Cocos Plate subducts beneath the continental North American Plate along the Middle American Trench. Both earthquakes caused significant damage and loss of life. Initial United States Geological Survey (USGS) results show that these intermediate depth (50-60 km depth) earthquakes did not occurred along the plates interface, but ruptured the subducting oceanic plate with extensional faulting. These were not the typical subduction plate boundary compressional events along the subduction interface of the Middle American Trench.  Furthermore, the earthquakes were located about 640-km from each other, a far enough distance to suggest no link between them.  We will investigate several questions remaining about these earthquakes including: Will these earthquakes load the upper plate and possibly trigger an equal or larger earthquake on the plate interface? Are these the result of plate bending?  Do the aftershocks migrate to the locked zone in the subduction zone?  Did these intermediate depth earthquakes rupture into the mantle? Why did the intermediate depth earthquakes create so much damage? Are these earthquakes linked due to dynamic stresses? We will address these questions by deploying seismic sensors around these two earthquakes and in between them and analyzing the data collected in coordination with our colleagues in Mexico.We propose to immediately deploy 10 broadband and 50 UTEP-owned nodes (5-Hz, 3-component geophones) seismometers near the epicenters of the September 7 Chiapas, Mexico (M=8.1) and the September 19 Puebla, Mexico (M=7.1) earthquakes to record their aftershocks and to map shallow earth structure near heavily damaged regions. Initial United States Geological Survey (USGS) results show that the two largest earthquakes were unusual: neither earthquake occurred along the plate interface, both were at intermediate depth (50-60 km depth), and both earthquakes ruptured within the subducting oceanic plate with extensional faulting, not the typical subduction plate boundary compressional events along the Middle American Trench.  Furthermore, the earthquakes were ~640-km apart, longer than two fault lengths, a distance at which static triggering forces tend to be very small, suggesting no link between them. The 10 broadband instruments will be deployed for 6 months, while the nodes will be deployed 30 days, since this is the extant of their battery life. The nodes, however, allow for numerous stations to be deployed rapidly in targeted regions, especially regions of extensive damage for site characterization, and this is the first test of these instruments for this type of deployment. We wish to address some key questions on the earthquakes, defined above. Analysis of the data collected will allow for fault plane identification from aftershock locations, stress release and orientation caused by the earthquakes from the determination of fault plane solutions, and for site characterization and site effects to be mapped in regions of extensive damage. Furthermore, the data can be used to image the region to better define the active plate boundaries.

9月7日墨西哥恰帕斯州（M=8.1）和9月19日墨西哥普埃布拉（M=7.1）地震发生在沿着俯冲带，海洋科科斯板块沿着沿着中美洲海沟俯冲到北美大陆板块之下。这两次地震都造成了重大破坏和生命损失。美国地质调查局（USGS）的初步结果表明，这些中等深度（50-60 km深度）的地震并不是沿着板块界面发生的，而是通过伸展断层作用使俯冲的海洋板块破裂。这不是典型的沿着中美洲海沟俯冲界面的俯冲板块边界挤压事件。此外，地震彼此相距约640公里，距离足够远，表明它们之间没有联系。我们将调查关于这些地震的几个遗留问题，包括：这些地震是否会对上层板块产生负荷，并可能在板块界面上引发同等或更大的地震？这些是板弯曲的结果吗？ 余震会迁移到俯冲带的锁定带吗？ 这些中等深度的地震是否破裂到地幔中？为什么中深度地震会造成如此大的破坏？这些地震是由于动态应力而联系在一起的吗？我们将通过在这两次地震周围和之间部署地震传感器，并与墨西哥的同事协调分析收集的数据来解决这些问题。我们建议立即部署10个宽带和50个UTEP拥有的节点9月7日墨西哥恰帕斯地震震中附近的5赫兹三分量地震检波器（M=8.1）和9月19日墨西哥普埃布拉（M=7.1）地震，以记录其余震并绘制严重受损区域附近的浅层地球结构图。 美国地质调查局（USGS）的初步结果显示，这两次最大的地震是不寻常的：两次地震都没有发生在沿着板块界面，都在中等深度（50-60 km深度），而且两次地震都是在俯冲洋板块内破裂的，伴随着伸展断层作用，而不是典型的沿中美海沟沿着的俯冲板块边界挤压事件。此外，这两次地震相距约640公里，比两个断层的长度还长，在这个距离上，静态触发力往往非常小，这表明它们之间没有联系。10个宽带仪器将部署6个月，而节点将部署30天，因为这是它们电池寿命的剩余时间。然而，这些节点允许在目标区域，特别是大面积破坏的区域迅速部署许多台站，以确定场地特征，这是对这些仪器进行此类部署的第一次测试。我们希望解决上面定义的一些关于地震的关键问题，对收集到的数据进行分析，将允许从余震位置识别断层面，通过确定断层面解决方案确定地震引起的应力释放和方向，以及在大面积破坏地区绘制场地特征和场地效应。此外，这些数据可用于对该区域进行成像，以更好地定义活动板块边界。