Strength of continental lithosphere in western China from seismic body wave studies

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。板块构造学的基本原理之一是准刚性板块横过地球表面，在板块边界附近有明显的变形。虽然这一观点在海洋中很有效，但在大陆上必须进行大量修改。在大陆上，与大陆碰撞有关的活跃的造山活动和地震活动可能位于距离板块边界数千公里的地方。今天印度和欧亚大陆之间的碰撞可以说是最好的天然实验室，我们可以研究施加在岩石圈上的应力与产生的深度变形之间的关系。我们将调查塔里木盆地内部和周围的地震活动。在高度变形的青藏高原和天山山脉之间基本未变形的地区。这一地区发生地震（或不发生地震）的地方将帮助我们了解大陆的主体是如何对施加的压力作出反应的。这项工作将与新疆省地震局（中国）合作完成，并有望导致美中研究人员之间进一步的科学合作。我们的发现将促进我们对大陆地区岩石圈变形的认识。由于这种变形通常是通过破坏性地震完成的，我们的工作将对理解大陆地区的地震活动有直接的影响。具体成果将直接有利于中国新疆地区的地震灾害监测和减灾需求。地震活动代表了岩石圈对应力的响应，大陆岩石圈剧烈变形的区域是寻找岩石圈内部强度分布观测证据的最佳地点。支持大陆岩石圈定位的论据？上地壳和上地幔的强度部分依赖于大陆岩石圈中发生的罕见但重要的地壳下地震。然而，地震是否真的发生在大陆岩石圈的地壳之下，这一问题并没有得到普遍的认可。支持和反对地壳下岩石圈足够强大以允许脆性破坏的观点的争论取决于确定位于其中的地震震源。困难在于以前曾报道过次地壳地震的地区地震位置和地壳厚度的不确定性。一个这样的地区是塔里木盆地和周围的山区（昆仑和天山）。来自区域地震监测工作的数据，以前无法用于研究，将使我们能够为该地区的地震开发高度精确的震源参数，并以高保真度建立地壳-地幔过渡的深度。我们将以协调的方式进行地壳结构（使用远震体波方法）和局部地震的震源参数（使用区域质心矩张量反演）的分析。我们希望解决关键的不确定性（是否在地壳-地幔过渡之下有地震），并对区域岩石圈在深处变形的方式有细致的了解。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).One of the basic tenets of plate tectonics is that quasi-rigid plates traverse the surface of the Earth, with significant deformations confined to regions near plate boundaries. While this idea works well in the oceans, it has had to be modified substantially in the continents, where active mountain building and seismicity related to the continental collision can be located thousands of kilometers away from the plate boundary. The present-day continental collision between India and Eurasia is arguably the best natural laboratory were we can investigate relationships between stresses applied to the lithosphere and resulting deformation at depth. We will investigate seismic activity within and around the Tarim basin ? a largely un-deformed area between the highly deformed Tibetan Plateau and the Tien Shan mountains. Where earthquakes are (and are not) taking place in this region will help us understand how the body of the continent is responding to the stress applied.This work will be done in collaboration with the Provincial Bureau of Seismology in Xinjiang (China), and will hopefully lead to further scientific collaboration between US and Chinese researchers. Our findings will advance our understanding of the lithospheric deformation in continental regions. Since this deformation is often accomplished through destructive earthquakes, our work will have direct implications for understanding of seismic activity in continental regions. Specific results will directly benefit the seismic hazard monitoring and mitigation needs of the Xinjiang region of China.Seismic activity represents a response of the lithosphere to stress, and regions of intense deformation of continental lithosphere are the best places to find observational evidence for the strength distribution within it. Arguments in favor of locating continental lithosphere?s strength in both the upper crust and the uppermost mantle rely, in part, on the rare but significant occurrence of subcrustal earthquakes in the continental lithosphere. However, whether earthquakes do indeed occur beneath the crust of the continental lithosphere is not universally accepted. Arguments for and against the notion of subcrustal lithosphere being strong enough to permit brittle failure hinge on identifying earthquake hypocenters located within it. The difficulty arises from uncertainties in both earthquake locations and crustal thicknesses in areas where sub-crustal earthquakes have been previously reported. One such area is the Tarim basin, and the surrounding mountainous regions (Kunlun and Tien Shan). Data from the regional seismic monitoring efforts, previously not available for study, will enable us to develop highly accurate hypocentral parameters for earthquakes in the region, and also to establish with high fidelity the depth of the crust-mantle transition. We will perform, in a coordinated manner, analyses of crustal structure (using teleseismic body wave methods) and hypocentral parameters of local earthquakes (using regional centroid moment tensor inversions). We expect to resolve the key uncertainty (whether there are earthquakes below the crust mantle transition) and to develop a nuanced understanding of the way regional lithosphere is deforming at depth.