Development of a Teleseismic Viscoelastic Waveform Tomography Algorithm with Application to Broadband Seismograms from the Tien Shan

该项目包括两个部分：(1)调整一套波形层析成像算法，该算法基于R.G.Pratt和他的同事在过去18年中开发的2D声学框架，到目前为止仅用于活动震源环境中，用于分析远程地震的记录(通常被称为接收器函数？)以及(2)将该算法应用于在天山收集的宽带地震记录集合，作为最近完成的MANAS项目的一部分。第一部分背后的动机是这种方法被证明的有效性；可以在不诉诸大规模并行计算的情况下构建合理的模型。所涉及的任务包括将我们已经开发的这种代码的粘弹性版本结合到类似于声学情况中使用的伴随反演方案中。研究人员还将研究加入各向异性效应并将算法扩展到三维的可行性。第二部分的动机部分是我们对MANAS数据集的熟悉，但更多的是应用传统的？接收函数偏移和到达时间层析成像技术具体地说，到达时间层析成像图像显示，天山下方存在两个高波速板块，这表明该地区存在长期的板状岩石圈俯冲。接收器功能显示，在这些板块似乎被消耗的区域，莫霍面出现了不寻常的中断。这两幅图像对天山的演化都有一级含义，但分辨率不够。基于活动源类似物，波形层析成像方法将显著改善上地幔这些异常特征的图像质量。更好地了解这些特征将对我们估计这一地区的演化和世界这一地区地震活动的根本原因产生重大影响。我们掌握的关于地球内部的最好信息来源可能来自距离震源很远(1000公里)的地震仪记录。在过去十年中，一个特别富有成效的研究领域是对这些地震图的那些部分进行建模，这些部分被地震台下地表100公里以内的地球部分修改。在这个项目中，研究人员将开发一种新的技术，通过采用已被证明在更小规模的地下成像中非常有用的方法，从这些类型的波中提取更多信息。爆炸和振动器之类的震源。尽管尺度不同，但模拟波传播所涉及的基本物理是Samel。该算法将足够通用，让科学家和工程师在任何类似的环境中使用，以产生地下图像。

This project has two parts: (1) to adapt a suite of waveform tomography algorithms based on a 2D acoustic framework developed over the past 18 years by R. G. Pratt and co-workers and thus far used exclusively in an active source environment to the analysis of recordings of earthquakes at teleseismic distances (what are commonly known as ?receiver functions?) and (2) to apply this algorithm to a collection of broad band seismograms collected in the Tien Shan as part of the recently completed MANAS project. The motivation behind the first part is the demonstrated efficacy of this approach; reasonable models can be constructed without resorting to massively parallel computing. The tasks involved include incorporating a visco-elastic version of this code, which we have already developed, to an adjoint inversion scheme similar to that used in the acoustic case. The researchers will also investigate the feasibility of incorporating anisotropic effects and extending the algorithm to three-dimensions. The second part is motivated partly by our familiarity with the MANAS dataset, but more by results from the application of ?traditional? receiver function migration and arrival time tomography techniques. Specifically, arrival time tomography images indicate the presence of two high wavespeed slabs beneath the Tien Shan that suggest a long history of plate-like lithospheric subduction in this region. The receiver functions show an unusual disruption in the Moho in the areas where these plates appear to be consumed. Both these images have first order implications for the evolution of the Tien Shan, but interpretations suffer from insufficient resolution. Based on active source analogues, the waveform tomography approach will significantly improve the quality of the images of these unusual features in the upper mantle. A better understanding of these features will have a significant impact on our estimation of both the evolution of this region and the root cause of earthquake activity in this part of the world.Arguably the best sources of information we have about the interior of the Earth are derived from seismograph records of earthquakes recorded at long distances (1000 km) from the source. A particularly fruitful area of research over the past decade has been in modeling those parts of these seismograms that are modified by those parts of the Earth within a few 100 km of the surface beneath a seismic station. In this project the researchers will develop a new technique to extract more information from these types of waves by adapting methodology that has proved to be very useful in subsurface imaging on a much smaller scale using ?active? sources like explosions and vibrators. Despite the difference in scale, the basic physics involved in modeling wave propagation is the samel. The algorithm will be general enough for scientists and engineers to use in any analogous environment to produce subsurface images.