RAPID: Collaborative Research: Nepal Array Measuring Aftershock Seismicity Trailing Earthquake

在过去的5700万年里，印度和亚洲的碰撞创造了喜马拉雅山，世界上最高的山脉。 两个构造板块之间的会聚今天仍在继续，每年4厘米（1 ½英寸），使地球变形？喜马拉雅山的地壳，并造成大地震。 最近在尼泊尔发生的毁灭性地震（2015年4月25日7.8级; 2015年5月12日7.3级）就是这种活动的例子，尽管科学家认为过去发生过更大的地震，最高可达8.8级，并且在未来的某个时候将不可避免地再次发生。 这些地震中最大的一次可能会在印度北方和尼泊尔造成多达100万人死亡。 这些大地震在很大的区域内造成断层破裂，沿喜马拉雅山由西向东沿着约100至500公里。 最近尼泊尔地震发生的最大断层被称为主喜马拉雅逆冲断层。 科学家不知道为什么震级为7.8级？主震？地震发生的确切位置，加德满都西北100公里（60英里）;也不知道为什么地震断层停止移动约160公里（100英里）的东南偏东。 科学家们认为地震开始和停止的位置（称为？凹凸不平？）在那里断层面改变几何形状，也许在那里它变得更陡或不那么陡。 如果这些凹凸体相隔很远，地震可能会大得惊人;但如果凹凸体靠得很近，那么地震可能会较小。因此，为了量化喜马拉雅山的地震危险性，科学家们需要首先了解喜马拉雅主冲断层的几何形状。 在NAMASTE项目期间，美国科学家将与尼泊尔地震学家和学生合作，了解这种断层的几何形状，同时建设尼泊尔的科学能力。为了应对2015年4月25日尼泊尔喜马拉雅主冲断层上的M=7.8地震，来自UTEP和斯坦福大学的科学家正在尼泊尔东部紧急部署约20个宽带和短周期地震仪，覆盖了最大余震的区域 历史上，喜马拉雅大地震的余震发生在主俯冲带逆冲断层（主喜马拉雅逆冲断层）和展布逆冲断层（如主中央逆冲断层、主边界逆冲断层和主前缘逆冲断层）上。余震地震活动的详细位置将提供前所未有的地下分辨率的几何形状的这些断层，目前几乎完全从表面测绘。 知道现在哪些断层是活跃的吗？一个持续争议的话题将导致更好的印度-亚洲碰撞的运动学描述。 知道向下倾斜？斜坡和平地？喜马拉雅主冲断层的几何形状，特别是是否以及在何处存在沿走向的侧向斜坡，将导致更好地了解喜马拉雅大地震的历史记录，以及未来潜在的破裂带尺寸。 位于埃尔帕索的德克萨斯大学/斯坦福大学的20个测站阵列将补充俄勒冈州/加州大学滨江的一个测站阵列，这些测站阵列具有类似的规模和区域尺寸，共同获得整个余震区的综合图像，该余震区在各个方向上延伸到初始破裂区之外。 这两个阵列将保留约六个月。 该数据集将尽快提交给IRIS数据管理中心，供所有感兴趣的地震学家分析。

The collision of the India and Asia has created the Himalaya, the highest mountains in the world, over the last 57 million years. Convergence between the two tectonic plates continues today, at 4cm (1 ½ inches) per year, deforming the earth?s crust in the Himalaya, and creating great earthquakes. The recent devastating earthquakes in Nepal (April 25, 2015 magnitude 7.8; and May 12, 2015 magnitude 7.3) are examples of this activity, though scientists believe that far larger earthquakes have happened in the past, up to magnitude 8.8, and will inevitably occur again sometime in the future. The biggest of these earthquakes could kill as many as 1 million people in northern India and Nepal. These large earthquakes rupture faults over very large areas, perhaps 100 to 500 km West-East along the Himalaya. The biggest fault, on which the recent Nepal earthquakes occurred, is called the Main Himalayan Thrust. Scientists do not know why the magnitude 7.8 ?main shock? earthquake initiated exactly where it did, 100 km (60 miles) northwest of Kathmandu; nor why the earthquake fault stopped moving about 160 km (100 miles) to the east-south-east. Scientists believe earthquakes start and stop at locations (called ?asperities?) where the fault-plane changes geometry, perhaps where it becomes steeper or less steep. If these asperities are a long way apart, the earthquake can be devastatingly large; but if the asperities are close together, then the earthquakes are likely to be smaller. Hence, in order to quantify seismic hazard in the Himalaya, scientists need to first understand the geometry of the Main Himalayan Thrust. During Project NAMASTE, US scientists will work alongside Nepali seismologists and students to understand this fault geometry, while at the same time building the Nepali scientific capacity.In response to the April 25, 2015 M=7.8 earthquake on the Main Himalayan Thrust in Nepal, scientists from UTEP and Stanford are urgently deploying ~20 broadband and short-period seismometers in an areal array across eastern Nepal, spanning the region of the largest aftershocks. Historically, aftershocks of large Himalayan earthquakes occur on both the principal subduction-zone thrust (the Main Himalayan Thrust), and also on splay thrust faults such as the Main Central Thrust, Main Boundary Thrust and Main Frontal Thrust. Detailed location of the aftershock seismicity will provide unprecedented sub-surface resolution of the geometry of these faults that at present are known almost entirely from surface mapping. Knowing which faults are active at the present day ? a subject of ongoing controversy ? will lead to better kinematic descriptions of the India-Asia collision. Knowing the down-dip ?ramp-and-flat? geometry of the Main Himalayan Thrust, and particularly whether and where along-strike lateral ramps exist, will lead to better understanding of the historical record of great Himalayan earthquakes, and potential future rupture zone dimensions. The 20-station University of Texas at El Paso/Stanford University array will complement an Oregon State/University of California Riverside array of similar size and areal dimension to together acquire a comprehensive image of the entire aftershock zone that extends somewhat in all directions beyond the initial rupture area. Both arrays will remain in place for about six months. This dataset will be submitted as rapidly as possible to the IRIS Data Management Center for analysis by all interested seismologists.