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

该奖项由2009年美国复苏和再投资法(公法111-5)资助。板块构造学的基本原理之一是准刚性板块穿过地球表面，重大变形仅限于板块边界附近的区域。虽然这一想法在海洋中运作良好，但在大陆上必须进行实质性的修改，因为在大陆，与大陆碰撞相关的活跃的山脉建设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大陆碰撞可以说是最好的天然实验室，因为我们可以研究施加到岩石圈的应力和由此产生的深部变形之间的关系。我们将调查塔里木盆地内部和周围的地震活动？位于高度变形的青藏高原和天山山脉之间的一个基本上没有变形的地区。这项工作将与新疆地震局(中国)合作完成，并有望促进中美两国研究人员之间的进一步科学合作。我们的发现将促进我们对大陆地区岩石圈形变的理解。由于这种变形通常是通过破坏性地震完成的，我们的工作将对了解大陆地区的地震活动有直接影响。具体成果将直接惠及中国新疆地区的地震灾害监测和减灾需求。地震活动代表着岩石圈对应力的响应，大陆岩石圈强烈变形区是寻找大陆岩石圈内部强度分布的观测证据的最佳场所。支持大陆岩石圈定位的论点？S在上地壳和最上地幔中的强度部分取决于大陆岩石圈中罕见但重要的次地壳地震发生。然而，地震是否真的发生在大陆岩石圈的地壳之下并不是普遍接受的。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，取决于识别位于其内部的地震震源。造成这一困难的原因是，以前曾报告发生过次地壳地震的地区的地震地点和地壳厚度存在不确定性。其中一个地区是塔里木盆地及其周围的山区(昆仑和天山)。来自区域地震监测工作的数据以前无法研究，这将使我们能够为该区域的地震制定高度准确的震源参数，并高保真地确定地壳-地幔过渡的深度。我们将以协调的方式分析地壳结构(使用远震体波方法)和地方地震的震源参数(使用区域质心矩张量反演)。我们希望解决关键的不确定性(地壳-地幔过渡之下是否存在地震)，并对区域岩石圈在深部变形的方式产生细微差别的理解。

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.