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

RAPID：合作研究：尼泊尔阵列测量地震后的余震地震活动

• 批准号: 1545923
• 负责人: Simon Klemperer
• 金额: $ 2.93万
• 依托单位: Stanford University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-06-15 至 2017-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1545923&HistoricalAwards=false
• 关键词: RAPID; Collaborative; Research; Nepal; Array

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.

在过去的5700万年中，印度和亚洲的碰撞创造了喜马拉雅山，世界上最高的山脉。今天，两个构造板之间的融合仍在每年4厘米（1.5英寸），在喜马拉雅山中畸形地球，并造成了巨大的地震。尼泊尔最近发生的毁灭性地震（2015年4月25日7.8级； 2015年5月12日级7.3）是这项活动的例子，尽管科学家认为过去发生了更大的地震，直到8.8级，并且将来会再次发生。在印度北部和尼泊尔，这些地震中最大的地震可能杀死多达100万人。这些大地震在非常大的区域上发生破裂的断层，大概是喜马拉雅山西部100至500公里。最近发生的尼泊尔地震发生的最大错误被称为主要喜马拉雅推力。科学家不知道为什么幅度为7.8？主要冲击？地震始于加德满都西北100公里（60英里）的地震。也不是为什么地震断层停止移动约160公里（100英里）到东南东南。科学家认为，地震从地点开始和停止（称为？sperities？），断层平面会改变几何形状，也许是在钢铁中变成钢器或陡峭的地方。如果这些令人垂涎的相距很长，地震可能是毁灭性的。但是，如果浅层人群靠近，那么地震可能会较小。因此，为了量化喜马拉雅山的地震危害，科学家需要首先了解喜马拉雅主要推力的几何形状。在NAMASTE项目期间，美国科学家将与尼泊尔地震学家和学生一起了解这种故障几何形状，同时建立尼泊尔的科学能力。在对2015年4月25日的M = 7.8尼泊尔主要推力上的地震响应中，来自尼泊尔的主要喜马拉雅人推力，来自Utep和Stanford的科学家跨越了距离，并在北方的越野范围内，既宽广的又一个宽敞的杂物〜20宽阔的杂物〜尼泊尔，跨越最大余震的区域。从历史上看，大型喜马拉雅大地震的余震都发生在主要的俯冲区域推力（主要的喜马拉雅推力）上，也出现在the骨上的断层，例如主要的中央推力，主要边界推力和主要额前推力。余震地震性的详细位置将提供这些断层几何形状的前所未有的地下分辨率，而这些断层几乎完全来自表面映射。知道目前哪些故障活跃？持续争议的主题？将导致对印度 - 亚洲碰撞的更好的运动学描述。知道倾斜的坡道和flat吗？主要喜马拉雅主要推力的几何形状，尤其是是否存在横向横向斜坡的几何形状，将会更好地理解大喜马拉雅地震的历史记录以及潜在的未来破裂区维度。德克萨斯州埃尔帕索（El Paso）/斯坦福大学（Stanford University）的20座大学阵列将补充俄勒冈州/加利福尼亚大学河滨分校的尺寸和面积尺寸的阵列，以共同获得整个余震区的全面图像，该图像在最初的破裂区域以外的所有方向上延伸了一定的方向。两个阵列将保持大约六个月。该数据集将尽可能迅速地向IRIS数据管理中心提交，以供所有感兴趣的Seismologist提出分析中心。