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

两个板块碰撞时，如俯冲带或大陆碰撞带，沿板块边界沿着的运动通常是迎面而来的。在某些情况下，碰撞是倾斜的，这种情况形成了复杂的地壳变形模式。有些变形是由允许地壳块体相互滑动的断层所适应的，有些变形是由具有垂直和水平运动分量的褶皱和断层的发育所适应的。加勒比海板块和北美板块之间的边界就是这样一个例子。来自罗得岛大学、纽约城市大学和海地国家大学的一个科学家研究小组正在对海地的阿祖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移动以应对倾斜的板块碰撞。该地区特别令人感兴趣，因为研究区域位于2010年1月12日7.0级海地地震破裂带的东部，这场灾难性事件摧毁了首都太子港和周边地区。除了阐明如何沿沿着这一板块边界的运动是容纳，这项研究将提供一些重要的信息，需要一个有意义的评估面临的地震危险，这一人口稠密的地区。该项目将通过以下方式推进其他预期的社会成果：教育专业的学生参与该项目;通过研究生和本科生培训，发展多元化的、具有全球竞争力的STEM劳动力;与海地科学家密切合作。一级，加勒比板块正以相对于北美板块约2厘米/年的速度向东北偏东方向移动，这意味着两个板块之间的斜向会聚。两个东西向的左旋转换断层和一个走向西北-东南的褶皱冲断带之间的运动分割，部分地容纳了这种斜向会聚。令人惊讶的是，2010年Mw7.0海地地震并没有沿着Enriquillo-Plantain Garden断层（南部转换断层）的明确痕迹发生沿着破裂。相反，滑动发生在一个未知的盲斜逆冲断层，毗邻走滑断层。预计伊斯帕尼奥拉岛沿着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。特别是位于海地首都太子港以东约30公里处的Azuei湖，被Enriquillo-Plantain Garden断层一分为二，北部和东部以海地褶皱冲断带为界。该项目采用高分辨率多道地震反射勘测和CHIRP海底下剖面法，对走滑和逆冲褶皱结构在Azuei湖下交汇处进行成像，并确定它们之间的空间和时间关系。Azuei湖是一个浅水湖，位于2010年震中以东约60公里处，被Enriquillo-Plantain Garden断层穿过，并以海地褶皱和冲断带为界。为期两周的调查将产生一个高分辨率多通道地震反射剖面的密集网格，预计穿透深度至少在湖床以下几百米。将同时采集CHIRP浅地层剖面;这些剖面将提供更高的地层分辨率（亚米级），但穿透深度较低（最高达20米）。此外，将用一系列短沉积物岩心对地震地层进行地面验证。这些岩心将被放置在地震数据表明更深（更老）的地震层位与湖床相交的地方。沉积物样品将使用古地磁测量和放射性同位素方法相结合的日期，以建立一个全新世年代地层阿苏埃湖。对地震反射和CHIRP剖面进行仔细的地层分析，将得到断层、褶皱和层序边界的三维数字表示。该项目将结合沉积岩芯的地层分析，确定这两组斜向构造之间的空间和时间关系。

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.