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

在50公里以下和700公里深处发生地震是出乎意料的，因为这些深度的高压和高温。这种深层地震占全球所有地震的25%，发生在俯冲带，偶尔会对地表造成破坏，因此更好地了解它们发生的原因将有助于地震危害分析和准备。它还将帮助我们更好地了解地震可能发生的各种条件。这项工作将通过研究发生在南美洲西北部的一个独特的地震群的性质，为此类地震的可能机制提供新的限制。该项目不仅关注地震的发生和危害，而且通过培养地震学博士后来加强STEM教育，对社会有益。考卡中深度地震群位于哥伦比亚地下，震源深度在50-200公里之间，每年发生约58次地震，当地震级ML大于或等于2.5。地震既位于俯冲板块的平面地震带，也位于两个不同的柱状或指状，向板块上方延伸30-40公里，并进入地幔楔。利用哥伦比亚国家地震台网2010年至今的地震数据，考卡群地震将通过精确地重新定位地震，反演波形来计算许多较大地震的震源机制，并估计地震的静态和动态震源特性来表征。这些分析将首次提供地幔楔地震的特征，并对两种情况下地震的震源特性进行比较，从而能够测试不同的假设，例如脱水脆化、剪切不稳定、水力压裂和流体传播路径崩溃，以解释这些地震发生的原因。关于中深度地震的机制和流体通过地幔楔的迁移路径的新限制将适用于所有俯冲带。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.