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

9月7日墨西哥恰帕斯(M=8.1)和9月19日墨西哥普埃布拉(M=7.1)地震沿着俯冲带发生，大洋科科斯板块沿着中美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公里深)的地震并不是沿着板块界面发生的，而是伴随着伸展断层而破裂的俯冲洋板。这些都不是典型的沿中美海沟俯冲界面的俯冲板块边界挤压事件。此外，这些地震彼此之间的距离约为640公里，足够远的距离表明它们之间没有联系。我们将调查关于这些地震的几个剩余问题，包括：这些地震是否会加载上板块，并可能在板块界面上引发相等或更大的地震？这些是板块弯曲的结果吗？余震是否迁移到俯冲带的锁定带？这些中等深度的地震是如何破裂进入地幔的？为什么中深度地震会造成如此大的破坏？这些地震是由动应力引起的吗？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同事合作分析收集的数据来解决这些问题。我们建议立即在9月7日墨西哥恰帕斯(M=8.1)和9月19日墨西哥普埃布拉(M=7.1)地震的震中附近部署10个宽带和50个UTEP拥有的节点(5赫兹三分量地震检波器)地震仪，以记录他们的余震并绘制重灾区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，两次最大的地震并不寻常：两次地震都没有发生在板块界面上，都是在中等深度(50-60公里深)，两次地震都是在俯冲板块内破裂并伴有伸展断层，而不是典型的沿中美海沟的俯冲板块边界挤压事件。此外，两次地震相隔约640公里，长于两个断层长度，静态触发力往往很小，表明它们之间没有联系。这10个宽带仪器将部署6个月，而节点将部署30天。因为这是他们电池寿命的延续。然而，这些节点允许在目标区域迅速部署许多站点，特别是在场地特征方面受到广泛破坏的区域，这是对这些工具进行此类部署的第一次测试。我们希望解决关于上面定义的地震的一些关键问题。对收集的数据进行分析将能够从余震位置识别断裂面，从确定断裂面解决方案确定地震造成的应力释放和方向，并在广泛破坏的地区绘制场地特征和场地影响图。此外，这些数据还可以用来对该区域进行成像，以便更好地定义活动板块边界。

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.