Adjoint tomography of the crustal and upper-mantle seismic structure beneath Continental China

中国大陆地壳和上地幔地震结构的伴随层析成像

• 批准号: 1345096
• 负责人: Min Chen
• 金额: $ 25万
• 依托单位: William Marsh Rice University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-08-01 至 2017-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1345096&HistoricalAwards=false
• 关键词: Adjoint; tomography; crustal; upper; mantle

East Asia has drawn much attention of geoscientists due to its complicated zoo of tectonic activities: unique continent-continent collision of India and Asia, different styles of plate subduction, various types of hydrocarbon-bearing basin formation, widespread intracontinental rifting, intraplate volcanism and magamatism. Tracing the driving forces behind these tectonic activities is vital to understand how the ancient continental roots, continental and oceanic plates at the plate margins, and mantle flows underlying lithosphere interact amongst each other in a dynamic earth framework. It?s essential to obtain high-definition multi-parameter seismic images of the earth?s interior to test different hypotheses of the tectonic driving forces, such as crustal shortening or/and Indian plate underthrusting causing the uplift of ?the world?s roof?, the Tibetan Plateau, lower-mantle plume or/and dehydration from the stagnant slab in the mantle transition zone (410 ? 650 km depths) inducing hot mantle upwelling contributing to the intraplate volcano Changbaishan along the border of China and North Korea, and the Pacific slab subduction and rollback producing extension, transtension, and thinning of the lithosphere beneath the East China and opening of the marginal seas of Japan and South China. Seismic imaging in this study will map full waveforms of seismic records to render more realistic models representing the earth?s interior properties. The outcome will not only provide the independent and robust seismological constrains to test the end members of tectonic formation mechanism, but also shed new light on the composition, thermal state, flow and fabric structure of the lithosphere and upper mantle, which are complementary to geological, geochemical, petrological, and geodetic observations of East Asia.An unprecedented seismic waveform dataset recorded by very dense array stations in China and its surrounding regions will be used to image the crust and upper-mantle structure beneath the East Asia. This dataset is comprised of seismic records from the CEArray, the NECESSArray, the INDEPTH-IV Array, F-net and other global and regional seismic networks. Contrary to traditional ray-theory based seismic imaging, adjoint tomography of this study takes into account full 3D wave propagation effects and off-ray-path sensitivity. In this implementation, it utilizes a spectral-element method for precise wave propagation simulations. The tomographic method starts with a 3D initial model that combines the smooth radially anisotropic mantle model S362ANI with 3D crustal model Crust2.0 (potentially recently released Crust1.0 can be used for more accurate and higher resolution model refinement). Traveltime and amplitude misfits are minimized iteratively based on a conjugate gradient method, harnessing 3D finite-frequency kernels computed for each updated 3D model. The massively parallel simulations are carried out on XSEDE supercomputers available to the team via an existing XSEDE research allocation. The final models will allow close examination of seismic structures beneath different tectonic units of East Asia, and better understanding of how sub-surface processes shaping surface geology and tectonic features. The preliminary results already show strong correlations between heterogeneities in the crust and upper mantle with surface tectonic units, such as the Himalaya Block, the Tibetan Plateau, the Tarim Basin, the Ordos Block, and the Sichuan Basin. Narrow slab features emerge from the smooth initial model above the transition zone. 3D wavespeed variations in the preliminary model are either comparable to or sharper than high-frequency P- and S-wave tomographic images from previous studies. Additional iterations will be carried out to refine the 3D radially anisotropic models, and to resolve 3D azimuthal anisotropy and attenuation, which are closely related to mantle rheology and crustal and lithospheric strain rates and flow. This proposal will support one graduate student and one research scientist. The outcome of this research will also have a broader impact on understanding the linkage between 3D wavespeed heterogeneities and seismogenic processes. The more realistic high-definition models will help assess seismic hazard by providing more accurate ground motion maps, more robust slip predictions and rupture estimations on finite fault surfaces for future catastrophic earthquakes. The final models will be archived and distributed for quantitative studies in other fields of geoscience, such as geology, geochemistry, petrology, geodynamics and volcanology. With the existing 3D visualization lab facility at Rice, the earth models can be readily displayed to the public to promote earth science. Finally the results will enhance scientific communication between US and China and broaden future potential collaborations.

东亚由于其复杂的构造活动而备受地球科学家的关注：独特的印度-亚洲大陆碰撞，不同类型的板块俯冲，不同类型的含油气盆地形成，广泛的陆内裂谷作用，板内火山和岩浆作用。追踪这些构造活动背后的驱动力对于理解古代大陆根、板块边缘的大陆和海洋板块以及岩石圈下的地幔流如何在一个动态的地球框架中相互作用至关重要。它吗?获得高清晰度多参数地球地震图像必不可少？为了测试构造驱动力的不同假设，例如地壳缩短或/和印度板块下冲造成了？世界吗?屋顶?650 km深度)引起热地幔上涌，形成了中朝边界的长白山板块内火山，太平洋板块俯冲和回滚形成了中国东部岩石圈的伸展、张拉和减薄，并打开了日本和华南的边缘海。在这项研究中，地震成像将绘制地震记录的完整波形，以呈现更真实的代表地球的模型。S的内部性质。这一结果不仅为检验构造形成机制的末端成员提供了独立而有力的地震学约束，而且对岩石圈和上地幔的组成、热态、流动和结构结构有了新的认识，是对东亚地质、地球化学、岩石学和大地测量观测的补充。利用中国及其周边地区密集阵列台站记录的前所未有的地震波形数据集，对东亚地壳和上地幔结构进行成像。该数据集由来自cerarray、NECESSArray、INDEPTH-IV Array、F-net和其他全球和区域地震台网的地震记录组成。与传统的基于射线理论的地震成像不同，本研究的伴随层析成像考虑了全三维波传播效应和射线路径外灵敏度。在这个实现中，它利用谱元方法进行精确的波传播模拟。层析成像方法从三维初始模型开始，该模型结合了光滑径向各向异性地幔模型S362ANI和三维地壳模型甲壳2.0（可能最近发布的甲壳1.0可以用于更精确和更高分辨率的模型精化）。基于共轭梯度方法，利用为每个更新的3D模型计算的三维有限频率核，迭代地最小化旅行时间和振幅失配。通过现有的XSEDE研究分配，团队可以在XSEDE超级计算机上进行大规模并行模拟。最终的模型将允许仔细检查东亚不同构造单元下的地震结构，并更好地理解地下过程如何塑造地表地质和构造特征。过渡带上方光滑的初始模型出现窄板特征。初步模型中的三维波速变化与先前研究中的高频P波和s波层析成像图像相当，或者更清晰。进一步的迭代将细化三维径向各向异性模型，求解与地幔流变学、地壳和岩石圈应变速率和流动密切相关的三维方位各向异性和衰减。该提案将支持一名研究生和一名研究科学家。这项研究的结果也将对理解三维波速非均质性和孕震过程之间的联系产生更广泛的影响。更真实的高清模型将通过提供更精确的地面运动图、更可靠的滑动预测和有限断层表面的破裂估计，为未来的灾难性地震提供帮助，从而帮助评估地震危害。最后的模型将存档并分发给地球科学其他领域的定量研究，例如地质学、地球化学、岩石学、地球动力学和火山学。利用莱斯大学现有的3D可视化实验室设施，地球模型可以很容易地向公众展示，以促进地球科学。最后，研究结果将加强中美之间的科学交流，拓宽未来潜在的合作。