Collaborative Research: Deformation Processes in the Central Andaman Islands

2004年12月苏门答腊地震破坏了印度东部1000英里的板块边界，造成尼科巴岛和安达曼岛的破坏，使它们向西南方向移动了3 - 7米，并使它们向东倾斜。 虽然安达曼和尼科巴群岛的震动破坏很小，但倾斜对海岸线生态造成了巨大破坏。 数千公顷的农田被洪水淹没，在沉没的地区，森林海岸线已经开始受到侵蚀。在陆地上升的地方，数百公里的珊瑚礁被杀死，随之而来的是近岸渔场的丧失。然而，这显然不是第一次发生这种情况，而且可以肯定的是，它将再次发生。几个社会问题出现。这些灾难性的海啸地震发生的频率有多高？被洪水淹没的岛屿是永久淹没还是会慢慢恢复以前的水平？ 在未来几十年里，海岸线农田的盐水入侵和洪水泛滥是否会逆转或恶化？ 港口防御和码头是否需要扩建，以适应额外的淹没或出现。 苏门答腊地震在哪些方面与美国太平洋西北部预计的类似的Mw=9地震相似？ 从苏门答腊地震中可以学到什么，它适用于俄勒冈州和华盛顿的海岸？这些问题可以从苏门答腊/安达曼事件所涉及的地下过程的地球物理知识来回答。 在布莱尔港附近，安达曼/尼科巴群岛的大多数人都住在那里， 板块边界同时容纳印度板块的向北运动和安达曼板块的向西运动：每100年它容纳大约1米的向北运动和4米的会聚。 所有这些运动在地震中很少发生，但它是由缓慢的震间过程驱动的。来自孟菲斯和科罗拉多的科学家正在使用全球定位大地测量和海平面监测设备调查安达曼群岛的持续运动，以查明这些灾难性的变化是否正在增加或减少。随着时间的推移，这些影响的空间变化提供了独特的限制在岛上的持续过程。 他们的初步结果表明，尽管这些岛屿继续向西南方向移动，但一些沉降已经逆转。 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类测量。与隶属于安达曼和尼科巴生态学会的科学家达成了强有力的合作协议，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.