Mechanisms of Mantle Wedge and Intraslab Earthquakes Beneath Southwestern Colombia From Analysis of Earthquake Source Properties

从震源性质分析哥伦比亚西南部地幔楔和板内地震的机制

• 批准号: 1760802
• 负责人: Linda Warren
• 金额: $ 24.58万
• 依托单位: Saint Louis University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-04-15 至 2021-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1760802&HistoricalAwards=false
• 关键词: Mechanisms; Mantle; Wedge; Intraslab; Earthquakes

The occurrence of earthquakes below 50 kilometers depth, and as deep as 700 kilometers depth, is unexpected because of the high pressure and temperature at those depths. Such deep earthquakes, which represent ~25% of all earthquakes globally, occur in subduction zones and occasionally cause damage at the surface, so better understanding of why they occur will help with seismic hazard analysis and preparation. It will also help us to better understand the variety of conditions under which earthquakes can occur. This work will provide new constraints on the possible mechanisms of such earthquakes by studying the properties of a unique cluster of earthquakes that occur beneath northwestern South America. This project benefits society because of its focus on earthquake occurrence and hazard and because it enhances STEM education by training a postdoctoral fellow in seismology. The Cauca cluster of intermediate-depth earthquakes, which is located beneath Colombia between at depths of 50-200 kilometers, has ~58 earthquakes per year with local magnitude ML greater than or equal to 2.5. The earthquakes are located both in a planar seismic zone in the subducting slab and in two distinct columns, or fingers, extending 30-40 kilometers normal to and above the slab and into the mantle wedge. Using seismic data from 2010 to the present from the Colombian National Seismic Network, the Cauca cluster earthquakes will be characterized by precisely relocating the earthquakes, inverting waveforms to calculate focal mechanisms for many of the larger earthquakes, and estimating static and dynamic source properties for the earthquakes. These analyses will provide the first-ever characterization of mantle wedge earthquakes and a comparison of the source properties of earthquakes in two settings, thus enabling the testing of different hypotheses --- such as dehydration embrittlement, shear instability, hydrofracture, and collapse of fluid propagation pathways --- for why these earthquakes occur. The new constraints on the mechanisms of intermediate-depth earthquakes and fluid migration pathways through the mantle wedge will be applicable to all subduction zonesThis 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.

由于50公里以下和700公里深处的高压和高温，发生地震是意想不到的。这种深部地震约占全球所有地震的 25%，发生在俯冲带，偶尔会对地表造成损害，因此更好地了解它们发生的原因将有助于地震危险性分析和准备。它还将帮助我们更好地了解地震发生的各种条件。这项工作将通过研究南美洲西北部发生的一组独特地震的特性，为此类地震的可能机制提供新的限制。该项目对社会有益，因为它关注地震的发生和灾害，并通过培训地震学博士后来加强 STEM 教育。考卡中深度地震群位于哥伦比亚下方 50-200 公里深度之间，每年发生约 58 次当地震级 ML 大于或等于 2.5 的地震。这些地震既发生在俯冲板片的平面地震带中，也发生在两个不同的柱或指状地震带中，垂直于板片及其上方延伸 30-40 公里，进入地幔楔。 利用哥伦比亚国家地震台网 2010 年至今的地震数据，考卡组团地震的特征将包括精确重新定位地震、反演波形以计算许多较大地震的震源机制，以及估计地震的静态和动态震源特性。 这些分析将首次描述地幔楔地震的特征，并比较两种环境下的地震震源特性，从而能够测试不同的假设，例如脱水脆化、剪切不稳定、水力破裂和流体传播路径塌陷等，以解释这些地震发生的原因。 对中深度地震机制和穿过地幔楔的流体迁移路径的新限制将适用于所有俯冲带。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。