Collaborative Research: Interactions Between Transpressional Structures at the North American-Caribbean Plate Boundary: Geophysical Imaging Beneath Lake Azuei, Haiti

合作研究：北美-加勒比板块边界变形构造之间的相互作用：海地阿苏埃湖下方的地球物理成像

• 批准号: 1624556
• 负责人: Heather Sloan
• 金额: $ 13.61万
• 依托单位: Research Foundation Of The City University Of New York (Lehman)
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-11-01 至 2020-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1624556&HistoricalAwards=false
• 关键词: Collaborative; Research; Interactions; Between; Transpressional

Motion along plate boundaries where two plates collide, such as subduction or continental collision zones, is typically head-on. In some cases, the collisions are more oblique, a situation that sets up a complex pattern of crustal deformation. Some deformation is accommodated by faults that allow crustal blocks to slide by each other and some deformation is accommodated by development of folds and faults with both a vertical and horizontal component of motion. The boundary between the Caribbean and North American plates is such a case. A research team of scientists from the University of Rhode Island, City University of New York, and University d'Etat de Haiti is carrying out a seismic reflection and sediment coring study on Lake Azuei, Haiti, in order determine how the faults in this region are moving in response to oblique plate collision. This region is of particular interest because the study area lies just to the east of the rupture zone of the January 12, 2010 magnitude 7.0 Haiti earthquake, the catastrophic event that devastated the capital Port-au-Prince and surrounding regions. In addition to shedding light on how motion along this plate boundary is accommodated, this study will provide some critical information needed for a meaningful assessment of the seismic hazards facing this densely populated region. The project will advance other desired societal outcomes through: involvement of education major students in the project; development of a diverse, globally competitive STEM workforce through graduate and undergraduate student training; and close collaboration with Haitian scientists.To a first order, the Caribbean plate is moving east-northeastward at about 2 cm/yr relative to the North American plate, implying an oblique convergence between the two plates. This oblique convergence is partly accommodated across the island of Hispaniola by the partitioning of motion between two east-west left-lateral transform faults and a fold-and-thrust belt that strikes northwest-southeast. Surprisingly, the 2010 Mw7.0 Haiti earthquake did not rupture along the well-defined trace of the Enriquillo-Plantain Garden Fault, the southern transform fault. Instead, slip occurred on an unsuspected blind oblique thrust fault that abuts the strike-slip fault. Similar hazardous interactions between strike-slip and thrust faults are expected elsewhere along Hispaniola. In particular, Lake Azuei, located about 30 km east of Haiti's capital city of Port-au-Prince, is bisected by the Enriquillo-Plantain Garden Fault and is bounded to the north and east by the Haiti fold-and-thrust belt. This project employs a high-resolution multichannel seismic reflection survey and CHIRP sub-bottom profiling to image both strike-slip and thrust-fold structures where they meet beneath Lake Azuei and will determine the spatial and temporal relations between them. Lake Azuei, a shallow lake located about 60 km east of the 2010 epicenter, is crossed by the Enriquillo-Plantain Garden Fault and is also bounded by the Haiti fold-and-thrust belt. A two-week survey will produce a dense grid of high-resolution multichannel seismic reflection profiles with an expected penetration of at least a few hundred meters below the lake bed. CHIRP subbottom profiles will be acquired concurrently; these will provide an even higher stratigraphic resolution (sub-meter) but with a lower penetration (up to 20 m). In addition, the seismic stratigraphy will be ground-truthed with a series of short sediment cores. These cores will be sited where seismic data indicate that deeper (older) seismic horizons intersect the lake bed. Sediment samples will be dated using a combination of paleomagnetic measurements and radioisotopic methods in order to establish a Holocene chronostratigraphy for Lake Azuei. The careful stratigraphic analysis of the seismic reflection and CHIRP profiles will result in a digital representation of faults, folds, and sequence boundaries in three-dimensions. Together with the stratigraphic analysis of the sediment cores, this project will thus characterize the spatial and temporal relations between the two sets of oblique structures.

沿着两个板块碰撞的板块边界（例如俯冲带或大陆碰撞带）的运动通常是正面的。在某些情况下，碰撞更加倾斜，这种情况会产生复杂的地壳变形模式。一些变形是由允许地壳块相互滑动的断层来调节的，而另一些变形则是通过具有垂直和水平运动分量的褶皱和断层的发育来调节的。加勒比板块和北美板块的边界就是这样的情况。来自罗德岛大学、纽约城市大学和海地大学的科学家组成的研究小组正在海地阿苏埃湖进行地震反射和沉积物取芯研究，以确定该地区的断层如何因倾斜板块碰撞而移动。该地区特别令人感兴趣，因为研究区域位于 2010 年 1 月 12 日海地 7.0 级地震的破裂带以东，这场灾难性事件摧毁了首都太子港及周边地区。除了揭示如何适应沿着板块边界的运动之外，这项研究还将提供一些关键信息，以便对这个人口稠密地区面临的地震危害进行有意义的评估。该项目将通过以下方式推进其他期望的社会成果： 教育专业学生参与该项目；通过研究生和本科生培训，培养多元化、具有全球竞争力的 STEM 劳动力队伍；并与海地科学家密切合作。 首先，加勒比板块相对于北美板块以每年约 2 厘米的速度向东北偏东移动，这意味着两个板块之间存在倾斜汇聚。伊斯帕尼奥拉岛上的这种倾斜汇聚部分是通过两条东西向左旋转换断层和一条西北-东南走向的褶皱逆冲带之间的运动划分来调节的。令人惊讶的是，2010 年海地 Mw7.0 地震并没有沿着恩里基洛-车前草花园断层（南部转换断层）的明确轨迹发生破裂。相反，滑动发生在与走滑断层相邻的一个未曾预料到的盲斜逆冲断层上。预计伊斯帕尼奥拉岛沿线的其他地方也会出现走滑断层和逆冲断层之间类似的危险相互作用。特别是阿苏埃湖，位于海地首都太子港以东约30公里处，被恩里基略-车前草花园断层一分为二，北部和东部以海地褶皱逆冲带为界。该项目采用高分辨率多道地震反射勘测和 CHIRP 海底剖面对走滑结构和逆冲褶皱结构在阿苏伊湖下交汇处进行成像，并确定它们之间的时空关系。阿苏埃湖是一个浅湖，位于 2010 年震中以东约 60 公里处，恩里基洛-车前草花园断层穿过，也以海地褶皱逆冲带为界。为期两周的勘测将产生高分辨率多道地震反射剖面的密集网格，预计渗透到湖床以下至少数百米。同时获取 CHIRP 海底剖面；这些将提供更高的地层分辨率（亚米级），但穿透力较低（最多 20 m）。此外，地震地层学将通过一系列短沉积岩芯进行地面实测。这些岩心将位于地震数据表明较深（较旧）的地震层位与湖床相交的位置。将结合古地磁测量和放射性同位素方法对沉积物样本进行测年，以便建立阿苏埃湖的全新世年代地层学。对地震反射和 CHIRP 剖面的仔细地层分析将产生断层、褶皱和层序边界的三维数字表示。结合沉积物岩心的地层分析，该项目将描述两组倾斜结构之间的时空关系。