The Bucaramanga Nest: A Natural Laboratory for Exploring the Mechanics of Intermediate Depth Earthquakes

大多数地震发生在地壳浅层，但也有一些发生在更深的地方。 这些中深度地震发生在地壳和上地幔的构造板块，是俯冲到地球深部的碰撞板块边界。 除此之外，我们对为什么这些地震发生在某些地方缺乏了解（例如，哥伦比亚，阿富汗，罗马尼亚，北方卡斯卡迪亚），但不是在其他看似相似的碰撞板块边界。 我们也缺乏一个模型来解释它们的复发，即，为什么会发生 虽然不像浅层地震那样致命，但中深度地震偶尔也会造成毁灭性的破坏。 例如，1939年智利奇兰中深度地震造成约28，000人死亡，是该国历史上迄今为止最致命的地震。 中等深度的地震也会造成相当大的破坏。 例如，2001年华盛顿的尼斯夸利地震造成了超过20亿美元的损失，尽管它位于大都市西雅图的南部边缘。 本研究的重点是在哥伦比亚布卡拉曼加下的中深地震的强烈“巢”。 该地区是世界上中深度地震最集中的地区，它们的频繁发生意味着这是世界上研究它们的最佳机会。 通过使用最先进的哥伦比亚国家地震网络的数据，我们将更深入地了解这些地震是如何发生的。 虽然他将得到自己机构的资助，但该项目将有助于建立哥伦比亚和美国之间的合作。 它还将帮助发展中国家发展地震监测和评估能力。 我们对中深地震的认识应该广泛适用于世界各地的类似地震，包括美国太平洋西北部。这个为期三年的项目将与哥伦比亚波哥大安第斯山脉大学的German Prieto教授合作进行，将研究布卡拉曼加地下中深地震的强烈集中，哥伦比亚国家地震台网波形数据的最新分析。 我们将使用基于互相关的测量来开发：精确的地震位置，改进的3D速度结构，以及这些事件的更准确的源参数估计。 其结果将是更好地了解地震在布卡拉曼加巢，特别是一般的中深度地震。 我们将讨论的问题包括：这些地震是否是由于加勒比和纳斯卡板块在深度上的碰撞而发生的？ 它们是出现在可辨别的断层面上还是扩散到俯冲板片中？ 是否有Vp/Vs异常可能表明孔隙流体在其发生中的作用？ 中深源地震的震源性质如何随地震规模而变化？ 我们能识别重复的地震吗？如果是的话，它们的复发是否是非泊松的（即，在时间上不是随机的，而是由物理驱动的过程（如弹性反弹）控制的？ 是什么控制着布卡拉曼加地下中深地震的最大规模？ 我们的研究结果如何能够用于对世界各地中深度地震的规模和复发进行有用的限制，这将有助于灾害定性？该项目得到了国际科学和工程办公室地球物理方案和哥伦比亚方案的支持。

Most earthquakes occur in the Earth's shallow crust, but some are located at greater depth. These intermediate-depth earthquakes occur in the crust and upper mantle of tectonic plates that are subducting into the deep Earth at collisional plate boundaries. Beyond this, we lack an understanding of why these earthquakes occur at some places (e.g., Colombia, Afghanistan, Romania, northern Cascadia), but not at other, seemingly similar, collisional plate boundaries. We also lack a model that explains their recurrence, i.e., why they occur when they do. While not as deadly as shallow earthquakes, intermediate-depth earthquakes can occasionally be devastating. For example, the 1939 Chillan, Chile intermediate-depth earthquake killed ~28,000 people, and is by far the deadliest earthquake in that country's history. Intermediate-depth earthquakes can also be quite damaging. For example, the 2001 Nisqually, Washington earthquake caused over $2 billion in losses, despite being located on the southern fringe of metropolitan Seattle. The focus of this study is the intense "nest" of intermediate-depth earthquakes under Bucaramanga, Colombia. This area hosts the greatest concentration of intermediate-depth earthquakes in the world, and their frequent occurrence means that this presents the best opportunity in the world to study them. By using data from the state-of-the-art Colombian National Seismic Network, we will gain a deeper understanding into how these earthquakes work. Although he will be supported with funding from his own institution, this project will help build collaborations between Colombia and the US. It will also help develop capacity for earthquake monitoring and evaluation in the developing world. The understanding of intermediate-depth earthquakes that we develop should be broadly applicable to similar earthquakes worldwide, including the Pacific Northwest of the US.This three-year project, to be carried out in collaboration with Professor German Prieto of the University of the Andes in Bogota, Colombia, will study the intense concentration of intermediate-depth earthquakes under Bucaramanga, Colombia using state-of-the-art analysis of waveform data from the Colombian National Seismic network. We will use cross-correlation-based measurements to develop: precise earthquake locations, improved 3D velocity structure, and more accurate source parameter estimates of these events. The result will be a better understanding of earthquakes in the Bucaramanga Nest in particular, and intermediate-depth earthquakes in general. Among the questions we will address are: Do these earthquakes occur due to collision of the Caribbean and Nazca Plates at depth? Do they occur on discernable fault planes or are they diffuse throughought the subducting slab? Are there Vp/Vs anomalies that might indicate a role for pore fluids in their occurence? How do the source properties of intermediate-depth earthquakes vary with earthquake size? Can we identify repeating earthquakes, and if so, is their recurrence non-Poissonian (i.e., not random in time, but governed by a physically motivated process like elastic rebound)? What controls the maximum size of intermediate-depth earthquakes under Bucaramanga? How can the results of our study be used to place useful constraints on the size and recurrence of intermediate-depth earthquakes around the world that will be useful for hazard characterization?This project is supported by the Geophysics Program and the Colombia Program of the Office of International Science and Engineering.