Investigating Flat Slab Subduction and Plate Edge Tectonics in Northern South America

研究南美洲北部的平板俯冲和板块边缘构造

• 批准号: 1459047
• 负责人: Alan Levander
• 金额: $ 59.98万
• 依托单位: William Marsh Rice University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-07-15 至 2019-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1459047&HistoricalAwards=false
• 关键词: Investigating; Flat; Slab; Subduction; Plate

The northern South American countries of Colombia and Venezuela have high seismic hazard. These countries are subject to frequent large earthquakes along strike-slip fault systems and subduction zones with the same combined seismic hazard potential as California's San Andreas system, and Oregon, Washington, and Alaska's subduction zones. Recent space geodesy measurements suggest that northwestern South America is overdue for a great (M8) earthquake along the flat Caribbean subduction zone under northern Colombia and the Lake Maracaibo region. Although both countries have modern earthquake monitoring and seismic hazard assessment agencies, Fundación Venezolana de Investigaciones Sismológicas (FUNVISIS) and Servico Geológico Colombiano (SGC), seismic hazard in both nations is exacerbated by poor, unregulated construction practices and a growing population of urban poor. The two nations have a combined population of ~80 million, and rapidly growing urban populations. Both the Venezuelan and Colombian civil and petroleum infrastructures are at risk from large seismic events. For a variety of reasons, including proximity, both Venezuela and Colombia are of strategic significance to the U.S. [Miami and New Orleans are closer to Bogota and Caracas than they are to Seattle, for instance]. Venezuela is of international importance, with hydrocarbon reserves that exceed Saudi Arabia's and extensive hydrocarbon production facilities. Venezuela currently supplies the U.S. with ~ 8% of its oil imports, only slightly less than imports from Saudi Arabia. The U.S. is Venezuela's most important trading partner. Scientific exchange between the U.S. and Venezuela and Colombia is important for developing scientific capacity in these nations, and for training their earth science workforces. Over the course of its history, the Rice Earth Science department has continuously enrolled M.Sc. and Ph.D. students from Venezuela and Colombia. Roughly 10% of modern subduction zones exhibit flat slab segments, including 3-4 along western South American (SA). Geologic history suggests ~70% of the western SA margin experienced flat subduction in the Cenozoic. Slab flattening is attributed to slab buoyancy, mantle wedge properties, and mantle flow dynamics. Flat subduction causes deformation in the overriding plate substantially different than that caused by normal subduction, as seen in seismicity, type and distribution of magmatism, and in some cases, basement cored uplifts. It is now recognized that the Caribbean subducts at low angles under northwestern SA, forming the basement cored uplifts of the Santa Marta, Perija, and Merida Andes ranges. These may be modern analogs to the late Mesozoic-early Cenozoic Laramide basement uplifts of the western United States. With FUNVISIS and SGC, the investigator team will install a large broadband seismograph array to image the subduction zone geometry and measure plate coupling rheology of the northern SA flat slab, with a goal of understanding the geodynamic development of basement uplifts. The local and regional earthquakes recorded by their seismograph array will be used for seismic hazard assessment in northern South America.

南美洲北部的哥伦比亚和委内瑞拉有很高的地震危险。这些国家沿着走滑断层系统和俯冲带频繁发生大地震，与加利福尼亚州的圣安德烈亚斯系统、俄勒冈州、华盛顿州和阿拉斯加州的俯冲带具有相同的地震危险性。最近的空间大地测量测量表明，沿着哥伦比亚北部和马拉开波湖地区平坦的加勒比海俯冲带，南美洲西北部早该发生一次大地震（8级）了。尽管这两个国家都有现代化的地震监测和地震灾害评估机构Fundación Venezolana de Investigaciones Sismológicas （FUNVISIS）和Geológico columbiano (SGC)，但两国的地震灾害都因不规范的不良建筑实践和不断增长的城市贫困人口而加剧。这两个国家的总人口约为8000万，城市人口也在迅速增长。委内瑞拉和哥伦比亚的民用和石油基础设施都面临着大型地震事件的风险。由于各种原因，包括地理位置，委内瑞拉和哥伦比亚对美国都具有战略意义（例如，迈阿密和新奥尔良离波哥大和加拉加斯比离西雅图更近）。委内瑞拉在国际上具有重要意义，其油气储量超过沙特阿拉伯，拥有广泛的油气生产设施。委内瑞拉目前向美国提供了约8%的石油进口，仅略低于从沙特阿拉伯的进口。美国是委内瑞拉最重要的贸易伙伴。美国与委内瑞拉和哥伦比亚之间的科学交流对于发展这些国家的科学能力以及培训它们的地球科学工作人员非常重要。在其历史进程中，莱斯大学地球科学系不断招收来自委内瑞拉和哥伦比亚的硕士和博士学生。大约10%的现代俯冲带呈现平板段，包括沿南美西部（SA）的3-4个。地质历史表明，西南缘约70%的地区在新生代经历了平坦俯冲。板块变平归因于板块浮力、地幔楔特性和地幔流动动力学。从地震活动性、岩浆活动的类型和分布，以及某些情况下的基底岩心隆起来看，平坦俯冲导致上覆板块的变形与正常俯冲造成的变形有很大不同。现在已经认识到加勒比海在西北角俯冲，形成了圣玛尔塔、佩里哈和梅里达安第斯山脉的基底核隆升。这些可能与美国西部中生代晚期-新生代早期的拉腊米基底隆起有现代相似之处。利用FUNVISIS和SGC，研究小组将安装一个大型宽带地震仪阵列，对俯冲带的几何形状进行成像，并测量南太平洋北部平板的板块耦合流变学，目的是了解基底隆起的地球动力学发展。他们的地震仪阵列记录的局部和区域地震将用于南美洲北部的地震危险性评估。