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较浅的地方，但也有一些地震发生在较深的地方。这些中深度地震发生在板块碰撞边界处俯冲到地球深处的构造板块的地壳和上地幔中。除此之外，我们对为什么这些地震发生在一些地方(如哥伦比亚、阿富汗、罗马尼亚、卡斯卡迪亚北部)缺乏了解，但对其他看似相似的碰撞板块边界却没有。我们也缺乏一个模型来解释它们的反复出现，即它们为什么会在它们发生时发生。虽然不像浅层地震那样致命，但中等深度的地震偶尔也会造成毁灭性的影响。例如，1939年智利奇兰中深地震造成约2.8万人死亡，是该国历史上死亡人数最多的一次地震。中等深度的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造成了超过20亿美元的损失，尽管它位于西雅图大都市的南部边缘。这项研究的重点是哥伦比亚布加拉曼加地下中深度地震的强烈“巢”。这一地区是世界上中等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好机会。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是如何发生的。尽管他将得到自己机构的资金支持，但这个项目将有助于在哥伦比亚和美国之间建立合作。它还将有助于发展发展中国家的地震监测和评估能力。我们对中等深度地震的理解应该广泛适用于世界各地的类似地震，包括美国的太平洋西北部。这一为期三年的项目将与哥伦比亚波哥大安第斯大学的德国·普雷托教授合作开展，将利用对哥伦比亚国家地震台网波形数据的最新分析，研究哥伦比亚布加拉曼加海底的中等深度地震的密集程度。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，以及对这些事件的更准确的震源参数估计。其结果将是更好地了解特别是布卡拉曼加Nest的地震，以及一般的中等深度地震。我们将解决的问题包括：这些地震是由于加勒比海板块和纳斯卡板块在深处碰撞而发生的吗？它们是发生在可识别的断裂面上，还是弥漫在俯冲板块中？是否存在可能指示孔隙流体在其发生中所起作用的Vp/VS异常？中深度地震的震源性质如何随地震规模的变化而变化？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，但受物理激励的过程，如弹性反弹所支配)？是什么控制了布卡拉曼加地区中深度地震的最大规模？如何利用我们的研究结果对世界各地中等深度地震的大小和复发施加有用的限制，这将有助于确定危险程度？该项目得到了地球物理计划和国际科学与工程办公室哥伦比亚计划的支持。