Collaborative Research: High Resolution Imaging of Deep Mantle Structure Using USArray Data

本项目利用USArray Transportable Array （TA）和Backbone Array数据进行深部地幔结构高分辨率地震波成像。研究计划的设计是根据加利福尼亚区域网络数据获得的初步结果，随着美国西部TA站的逐步部署自然地扩大规模。我们正在分析横跨三个区域深层地幔的远震地震波：美国南部-墨西哥湾-中美洲-加勒比海，中太平洋，阿拉斯加和北美北部。利用TA数据提供的相对密集的70公里台站间距的地震方法正在得到应用。双阵波形叠加、三维层析模型中的基尔霍夫散射偏移、允许方位各向异性的剪切波分裂分析以及有限频率层析到达时间反演程序是应用于宽带P和S波形的主要方法。当初始TA部署完成后，相对于我们最近开发的Cocos板块和区域框架结构下的局部高分辨率模型，它将使深部地幔空间采样增加5倍。特别的努力集中在中美洲和墨西哥湾下的中深部地幔上，在层析模型中有证据表明，板状高速结构穿过下地幔，在D区广泛蔓延，可能与法拉龙板块和北美地下俯冲的悠久历史有关。利用到达时间分析和偏移方法，研究了深部地幔结构的速度梯度、结构连续性、结构结构和空间范围，并使用2D和3D合成建模来量化结构并验证成像程序的可靠性。对阿拉斯加俯冲带下的相应构造进行了分析，并将这两个汇聚带区域与中太平洋下的孤立构造进行了比较。我们正在评估板块物质、钙钛矿后相变、深部地幔动态流动和部分熔融对深部地幔结构的贡献。这些分析将与地球镜对浅层地幔结构的调查密切配合，结合基于其他人发现的接收器结构、岩石圈各向异性和上地幔旅行时间变化模型的修正。我们的目标是利用USArray数据，在了解深部地幔结构及其与北美大陆西移相关的中上部地幔流动的关系方面取得突破性进展。

0453944GarneroThis project utilizes USArray Transportable Array (TA) and Backbone Array data in high-resolution seismic wave imaging of deep mantle structure. The research plan is designed to scale naturally with the progressive deployment of TA stations in the western U.S, building upon initial results obtained using California regional network data. We are analyzing teleseismic earthquake waves that traverse the deep mantle in three subregions: beneath the southern U.S.-Gulf of Mexico-Central America-Caribbean, under the Central Pacific, and beneath Alaska and northern North America. Seismic methodologies that exploit the relatively dense 70-km station spacing provided by the TA data are being applied. Double-array waveform stacking, Kirchhoff scattering migration in 3D tomographic models, shear-wave splitting analysis allowing for azimuthal anisotropy, and finite frequency tomographic arrival time inversion procedures are the primary methods being applied to broadband P and S waveforms. When the initial TA deployment is completed, it will enable 5-fold increase in deep mantle spatial sampling relative to recently developed localized high resolution models for beneath the Cocos Plate and regional framework structures that we have developed. Particular effort is being focused on the mid- and deep mantle beneath Central America and the Gulf of Mexico, where there is evidence in tomographic models for tabular high velocity structures extending through the lower mantle and spreading broadly in the D" Region, possibly associated with the Farallon slab and with the long history of subduction beneath North America. The velocity gradients, structural continuity, structural fabric, and spatial extent of the deep mantle structure is being examined using arrival time analysis and migration methods, with 2D and 3D synthetic modeling being used to quantify structures and to verify the reliability of the imaging procedures. Corresponding structure beneath the subduction zone under Alaska is being analyzed, and these two convergent zone regions are being compared to the isolated structure under the Central Pacific. We are assessing contributions to deep mantle structure from slab material, a post-perovskite phase transition, deep mantle dynamic flow, and partial melting. These analyses will be closely coordinated with Earthscope investigations of shallow mantle structure, incorporating corrections based on models found by others for receiver structure, lithospheric anisotropy, and upper mantle travel time variations. Our goal is to exploit USArray data to make breakthrough advances in understanding of deep mantle structure and its relationship to mid- and upper-mantle flow associated with the westward movement of the North American continent.