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

布卡拉曼加巢：探索中深度地震力学的天然实验室

• 批准号: 1045684
• 负责人: Gregory Beroza
• 金额: $ 26.76万
• 依托单位: Stanford University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-04-15 至 2016-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1045684&HistoricalAwards=false
• 关键词: Bucaramanga; Nest; Natural; Laboratory; Exploring

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.

大多数地震发生在地壳浅层，但也有一些地震发生在更深的地方。 这些中深度地震发生在构造板块的地壳和上地幔中，这些板块在碰撞板块边界处俯冲到地球深处。 除此之外，我们不明白为什么这些地震发生在某些地方（例如哥伦比亚、阿富汗、罗马尼亚、卡斯卡迪亚北部），而不是发生在其他看似相似的碰撞板块边界。 我们还缺乏一个模型来解释它们的复发，即它们为什么会发生。 虽然不像浅层地震那么致命，但中深度地震有时也会造成毁灭性的影响。 例如，1939 年智利奇廉发生的中深度地震造成约 28,000 人死亡，是该国历史上迄今为止最严重的地震。 中深度地震也可能造成相当大的破坏。 例如，2001 年华盛顿州尼斯夸利地震尽管位于西雅图大都市的南部边缘，却造成了超过 20 亿美元的损失。 这项研究的重点是哥伦比亚布卡拉曼加地下的强烈中深度地震“巢穴”。 该地区是世界上中深度地震最集中的地区，其频繁发生意味着这里提供了世界上研究中深度地震的最佳机会。 通过使用最先进的哥伦比亚国家地震台网的数据，我们将更深入地了解这些地震的发生机制。 尽管他将得到自己所在机构的资助，但该项目将有助于建立哥伦比亚和美国之间的合作。 它还将有助于发展发展中国家的地震监测和评估能力。 我们对中深度地震的理解应该广泛适用于世界各地的类似地震，包括美国西北部的太平洋地区。这个为期三年的项目将与安第斯大学的 German Prieto 教授合作进行哥伦比亚波哥大将利用哥伦比亚国家地震台网波形数据的最先进分析技术，研究哥伦比亚布卡拉曼加地下强烈集中的中深度地震。 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布卡拉曼加巢的地震，以及一般的中深度地震。 我们要解决的问题包括：这些地震是否是由于加勒比板块和纳斯卡板块在深处的碰撞而发生的？ 它们是出现在可辨别的断层面上还是在俯冲板片中扩散？ 是否存在可能表明孔隙流体在其发生过程中发挥作用的 Vp/Vs 异常？ 中深度地震的震源特性如何随地震规模变化？ 我们能否识别重复发生的地震？如果是的话，它们的复发是否是非泊松分布的（即，时间上不是随机的，而是受到弹性回弹等物理驱动过程的控制）？ 是什么控制着布卡拉曼加地下中深度地震的最大震级？ 我们的研究结果如何用于对世界各地中深度地震的规模和复发施加有用的限制，这将有助于灾害特征描述？该项目得到了地球物理学计划和哥伦比亚办公室的支持。国际科学与工程。