Collaborative Research: Deformation Processes in the Central Andaman Islands

2004年12月3日的苏门答腊岛Mw=9.3级地震使印度东部板块边界破裂1000英里，对尼科巴群岛和安达曼群岛造成了破坏，使它们向西南方向移动了3-7米，并向东倾斜。尽管安达曼和尼科巴群岛的摇晃破坏很小，但倾斜对海岸线生态造成了巨大的破坏。数千公顷的农田被洪水淹没，在下沉的地区，森林海岸线已经开始受到侵蚀。数百公里的珊瑚礁在陆地上升的地方被杀死，随之而来的是近岸渔场的丧失。但很明显，这已经不是第一次发生了，而且可以肯定的是，这种情况还会再次发生。这些灾难性的海啸地震多久发生一次？被洪水淹没的岛屿是永远被淹没了，还是会慢慢恢复到以前的水平？未来几十年，滨海农田的盐碱入侵和洪水泛滥会逆转或恶化吗？威尔港口的防御工事和码头需要扩建，以适应更多的潜水或浮现。苏门答腊岛地震与美国太平洋西北部预计发生的9级地震有何相似之处？苏门答腊岛地震对俄勒冈州和华盛顿州海岸有什么影响？这些问题可以从苏门答腊岛/安达曼地震所涉及的地下过程的地球物理知识中得到回答。在安达曼/尼科巴群岛大多数人居住的布莱尔港附近，板块边界既容纳了印度的北移，也容纳了安达曼板块的西移：每隔100年，它就容纳S大约1米的北移和4米的会聚。所有这些运动在地震中很少发生，但它是由缓慢的地震间过程驱动的。来自孟菲斯和科罗拉多州的科学家正在使用全球定位大地测量和海平面监测设备研究安达曼群岛的持续运动，以找出这些灾难性的变化是增加还是减少。这些效应随时间的空间变化为岛屿上的持续过程提供了独特的制约。他们的初步结果表明，尽管这些岛屿继续向西南方向移动，但一些下沉已经逆转。在这个为期两年的项目中，他们希望提供数百个点来限制未来的运动，并回答这些地震发生的频率。他们的目标之一是向当地科学家展示如何进行这种测量。与安达曼和尼科巴生态学会(SANE)的科学家建立了强有力的合作协定，这些科学家可以进入大多数岛屿。

The Mw=9.3 Dec 2004 Sumatra earthquake ruptured 1000 miles of India's eastern plate boundary causing damage in the Nicobar and Andaman islands, shifting them bodily 3m-7m southwestward, and tilting them down to the east. Although shaking damage in the Andaman and Nicobar islands was minor, the tilting caused massive damage to coastline ecologies. Thousands of hectares of agricultural land were flooded, and erosion of forested shorelines has commenced in regions that sank. Hundreds of km of coral reefs were killed where the land rose, with attendant loss of nearshore fishing grounds. Yet clearly this was not the first time that this has occurred, and it is certain that it will occur again.Several societal questions arise. How frequently do these catastrophic tsunami earthquakes occur? Are the flooded islands permanently drowned or will they slowly recover their former levels? Will the saline intrusion and flooding of shoreline farmland be reversed or worsened in the coming decades. Will harbor defenses and docks require extended construction to accommodate additional submergence or emergence. In what way does the Sumatra earthquake resemble a similar Mw=9 expected in the Pacific NW of the US? What can be learned from the Sumatra earthquake that has application to the coasts of Oregon and Washington?These questions can be answered from a geophysical knowledge of the subsurface process involved in the Sumatra/Andaman event. Near Port Blair, where most of the people of the Andaman/Nicobar islands live, the plate boundary accomodates both northward motion of India and the westward motion of the Andaman plate: every 100 years it accommodate s roughly1 m of northward motion and 4 m of convergence. All this motion occurs infrequently in earthquakes, yet it is driven by slow interseismic processes.Scientists from Memphis and Colorado are investigating continued movements in the Andaman islands using Global Positioning geodesy and sea level monitoring devices to find out whether these catastrophic changes are increasing or decreasing. The spatial variation of these effects with time provides unique constraints on the continuing processes in the islands. Their initial results indicate that although the islands continue to move SW some of the subsidence has been reversed. In this two year project they hope to provide many hundreds of points to constrain future motions, and to answer how frequently these earthquakes occur.One of their objectives is to show local scientists how to undertake these kinds of measurements. Strong collaborative agreements have been established with scientists affiliated with the Society for Andaman and Nicobar Ecology (SANE) who have access throughout most of the islands.