Collision of the Burma Arc Accretionary Prism and Foldbelt with the Ganges-Brahmaputra Delta in Bangladesh

在孟加拉国，苏门答腊岛俯冲带与世界上最大的恒河-雅鲁藏布江三角洲相遇，苏门答腊岛俯冲带是2004年12月毁灭性地震和海啸的源头。这两条大河排干了喜马拉雅山脉80%的面积，向孟加拉国排放了超过10亿吨的沉积物。这里有一个巨大的沉积物堆积物，它沿着大陆边缘向前推进了300多公里，进入了可能的洋壳，进入了俯冲带，用沉积物堵塞了它，并建立了一个巨大的空中吸积棱柱，这是从三角洲剥离出来的一条宽达300公里的褶皱和断层沉积物带。孟加拉的缅甸弧褶皱带是一个罕见的暴露在陆地上的海洋吸积棱柱。当大陆边缘的沉积物进入俯冲带时，它也代表了大陆碰撞的最早阶段。尽管有罕见的陆上吸积棱柱，但恒河-雅鲁藏布江三角洲和缅甸弧褶皱带的沉积物和地壳结构都鲜为人知。由于没有可靠的大地震历史记录，地震的危险性尚不清楚。在这个项目中，哥伦比亚大学的一个研究团队与达卡大学的科学家合作，正在开发对褶皱带结构及其运动学的基本第一手了解。正在三角洲和褶皱带部署一个地震仪网络。地震学研究将利用地震来阐明褶皱带中活动断层的几何形状，以及三角洲和褶皱带的沉积物和地壳结构。从恒河-雅鲁藏布江三角洲到褶皱带的全球定位系统部署将收集整个地区地表速度和变形的关键数据，并将与缅甸的全球定位系统调查挂钩，以获得对整个板块边界地带总缩短的第一次估计。地震学和大地测量数据集将得到工业地震和钻井数据的补充，用于该结构较浅的部分。总而言之，这些数据将提供有关活跃的海洋吸积棱柱前面的构造的前所未有的细节，该棱柱正被沉积物堵塞。该项目将有助于确定三角洲、增积棱柱和褶皱带的几何形状和运动，提供对缅甸弧形变量和变形方式的估计。它将提供超压吸积棱镜的力学信息。为了安全和具有成本效益的开发，迫切需要更好地了解孟加拉国正在进行的构造。在苏门答腊岛海沟的延续处，俯冲的速度有多快？两个板块之间的斜向运动如何在褶皱带中的不同构造之间分裂？这个被巨大沉淀物堆积堵塞的俯冲带能经受住大地震吗？无论是抗震滑动，还是朝着未来的大地震发展，对地球上人口最稠密的地区之一的地震风险都有着巨大的影响。这项研究将帮助孟加拉国发展关键基础设施和所使用的技术，并为评估地震风险提供依据。该项目将支持哥伦比亚大学的两名孟加拉研究生，他们将有望加强孟加拉国的基础设施。班格勒德西的科学家将在一系列研讨会上接受GPS和地震学方法方面的培训。该奖项由NSF国际科学与工程办公室共同资助。

In Bangladesh, the Sumatran subduction zone, source of the devastating December 2004 earthquake and tsunami, encounters the Ganges-Brahmaputra Delta, the world's largest. These two great rivers, which drain 80 percent of the Himalayan mountain range, discharge over 1 Gigaton of sediments into Bangladesh. This has an enormous sediment pile that has prograded the continental margin over 300 km, onto likely oceanic crust and enters the subduction zone, clogging it with sediment and building a huge, subaerial accretionary prism, an up to 300 km wide belt of folded and faulted sediments offscraped from the delta. The Burma Arc foldbelt in Bangladesh is a rare instance of an oceanic accretionary prism exposed on land. It also is representative of the earliest stage of continental collision as the sediments of a continental margin enter the subduction zone. It is overpressured and has the lowest slope of any accretionary prism.Despite the unusual occurrence of an onshore accretionary prism, the sediment and crustal structure of both the Ganges-Brahmaputra Delta and Burma Arc foldbelt are poorly known. With no reliable historical record of large earthquakes, the seismic hazard is unclear. In this project, a Columbia University research team working in collaboration with scientists from Dhaka University are developing a basic first-order understanding of the structure of the foldbelt and its kinematics. A seismometer network in the delta and foldbelt is being deployed. Seismological studies will use earthquakes to illuminate the geometry of active faults in the foldbelt and the sediment and crustal structure of the delta and foldbelt. A GPS deployment from the Ganges-Brahmaputra Delta to the foldbelt will gather critical data on the surface velocities and deformation across the region and will be tied to GPS surveys in Myanmar to obtain the first estimate of total shortening across the plate boundary zone. The seismological and geodetic data sets will be supplemented by industry seismic and well data for the shallower parts of the structure. Together, these data will provide unprecedented detail on the tectonics at the front of an active oceanic accretionary prism that is being choked with sediments. This project will help define the geometry and motions of the delta, the accretionary prism and the foldbelt, providing estimates of the amount and style of deformation taking place in the Burma Arc. It will provide information of the mechanics of overpressured accretionary prisms.A better understanding of the ongoing tectonics in Bangladesh is critically needed for safe and cost-effective development. How fast is the subduction at this continuation of the Sumatran trench? How does the oblique motion between the two plates split between different structures in the foldbelt? Does this subduction zone, choked by an enormous sediment pile sustain large earthquakes? Whether it is sliding aseismically or building toward a future large earthquake has enormous implications for the seismic hazard of one of the most densely populated regions on the earth. This study will help Bangladesh develop critical infrastructure and in the technologies used, and provide the basis for assessing earthquake hazard. This project will support two Bangladeshi graduate students at Columbia University, who will then hopefully strengthen the infrastructure in Bangladesh. Bangledeshi scientists will be trained in GPS and seismological methods in a series of workshops.This award was co-funded by NSF's Office of International Science and Engineering.