Collaborative research: A better understanding of seismic hazard in Tehuantepec, Mexico, using amphibious MT studies

合作研究：利用两栖 MT 研究更好地了解墨西哥特万特佩克的地震灾害

• 批准号: 2105776
• 负责人: Steven Constable
• 金额: $ 45.3万
• 依托单位: University of California-San Diego Scripps Inst of Oceanography
• 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: 2021-08-01 至 2024-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2105776&HistoricalAwards=false
• 关键词: Collaborative; research; better; understanding; seismic

The subduction zone offshore southwest Mexico is divided into two very different geological regions by the Gulf of Tehuantepec. North of the gulf, the Cocos tectonic plate is shallow as it subducts beneath the North American plate, earthquakes are less frequent, and the ocean trench is close to shore. At Tehuantepec the coastline bends to form the gulf, and south of the gulf the plate is steeper, earthquakes are more frequent, and the trench is far offshore. Located in between, the Gulf of Tehuantepec is considered a seismic gap, in that there have been no recorded large earthquakes associated with the tectonic plates slipping past each other. There are two possible reasons for this. The first is that the rocks of the Tehuantepec Ridge, which is being subducted with the Cocos plate, may be releasing water that lubricates the fault zone, allowing the plates to slowly slide past each other without producing large earthquakes. The second is that the topography of the ridge is mechanically locking the two plates together, in which case a very large earthquake is inevitable when the stress finally builds up to breaking point. In 2017 a large normal earthquake broke across the down-going Cocos plate, a type of earthquake not normally seen in subduction zones, and which could increase the stress and the chances of another large earthquake. This study will make geophysical measurements both onshore and offshore that are sensitive to the presence of water deep in the subduction zone to understand why this earthquake occurred. This work will advance the career of a postdoctoral investigator and strengthen ties between the US and Mexican geophysical communities.In this project an amphibious magnetotelluric (MT) sounding survey coupled with seismotectonic analysis will: (1) Determine differences in coupling/slip regimes in and around the Mexican Tehuantepec seismic gap; (2) Image the Tehuantepec Ridge within the subducted plate to determine its role in the coupling and if it contributes to the break between the Trans-Mexican Volcanic Belt arc system and the Chiapas arc; (3) Image any evidence of fluid infiltration in the Tehuantepec fault. MT soundings have already been successfully used in Mexico to identify changes between stick slip and transient slip within the subduction zone and the geometry of the lower plate. This new study will analyze the unusually large Mw8.2 normal fault Tehuantepec earthquake which is downdip of a slab interface that has no recorded earthquakes. The proposed reasons for why this earthquake occurred are that it was due to slab pull below a strongly coupled interface or that it was due to slab bending along a reactivated, possibly fluid-filled, and poorly coupled, subducted outer rise fault. This work would represent the only physical measurement to directly determine which is correct and determine the link to possible future earthquakes.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.

墨西哥西南部近海的俯冲带被特万特佩克湾分为两个截然不同的地质区域。 墨西哥湾以北，科科斯构造板块由于俯冲到北美板块之下而较浅，地震不太频繁，而且海沟靠近海岸。 在特万特佩克，海岸线弯曲形成海湾，海湾以南的板块更陡峭，地震更频繁，海沟远离海岸。 位于两者之间的特万特佩克湾被认为是一个地震空白区，因为没有记录到与构造板块相互滑动有关的大地震。 这可能有两个原因。 第一种是，正在与科科斯板块俯冲的特万特佩克海岭的岩石可能正在释放水，润滑断层带，使板块缓慢地相互滑动而不会产生大地震。 第二个原因是，海脊的地形机械地将两个板块锁定在一起，在这种情况下，当应力最终积累到断裂点时，一场非常大的地震是不可避免的。 2017年，一场大规模的正常地震穿过了下行的科科斯板块，这是一种在俯冲带中通常看不到的地震，可能会增加应力和另一场大地震的可能性。 这项研究将进行陆上和海上的地球物理测量，这些测量对俯冲带深处的水的存在很敏感，以了解这次地震发生的原因。这项工作将促进博士后研究人员的职业生涯，并加强美国和墨西哥地球物理界之间的联系。在这个项目中，两栖大地电磁测深（MT）测量与地震构造分析相结合将：（1）确定墨西哥特万特佩克地震空区及其周围的耦合/滑动机制的差异;（2）对俯冲板块内的特万特佩克海岭进行成像，以确定它在耦合中的作用，以及它是否促成了跨墨西哥火山带弧系和恰帕斯弧之间的断裂;（3）对特万特佩克断层中流体渗透的任何证据进行成像。墨西哥已成功地利用大地电磁测深确定俯冲带内粘滑和瞬时滑动之间的变化以及下板块的几何形状。这项新的研究将分析异常大的Mw8.2正断层特万特佩克地震，这是一个没有记录地震的板界面下倾。关于这次地震发生的原因，我们认为是由于强烈耦合界面下的板块拉力，或者是由于板块沿沿着一个重新激活的、可能充满流体的、耦合不良的俯冲外隆断层弯曲。这项工作将代表唯一的物理测量，以直接确定哪一个是正确的，并确定与未来可能的地震的联系。这个奖项反映了NSF的法定使命，并已被认为是值得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的支持。