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Seismic Anisotropy across the USArray using Surface-wave Arrival Angles

使用表面波到达角的 USArray 地震各向异性

基本信息

批准号：
1722579
负责人：
Gabriele Laske
金额：
$ 32.12万
依托单位：
University of California-San Diego Scripps Inst of Oceanography
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2017
资助国家：
美国
起止时间：
2017-07-01 至 2023-06-30
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1722579&HistoricalAwards=false
关键词：
Seismic Anisotropy across USArray using

项目摘要

The deployment of the USArray transportable array (TA) has allowed seismologists to compile seismic datasets and images with unprecedented detail. Seismic analyses of an extremely rich dataset of some 2000 stations have so far been based on 'standard' seismic data such as travel times. However, other kinds of data such as the particle motion of surface waves provide complementary observations to model smaller details in shallow Earth structure. The short distance between TA stations allows seismologists to trace in detail how surface waves from distant earthquakes bend around as they traverse the TA. This, in turn, can be used to fine-tune models of Earth structure beneath North America and improve scientists' understanding how the continent is made up.Certain mantle rocks exhibit seismic anisotropy where the speed at which seismic waves travel depend on the direction from which they approach. Anisotropy also forms when a plate, such as the North American plate, responds to forces tugging along its edges. Small subsets of TA stations can be used like antennas to measure the properties of this anisotropy. This, in turn, allows scientists to explore mantle processes that form, move and ultimately destroy Earth's plates. This project will collect both types of data.In global tomographic studies, surface-wave arrival angles have proven extremely useful to enhance the imaging of short-wavelength structure. Due to the sparseness of the global seismic networks the interpretation of such data were interpreted using perturbation theory to a great-circle approach. The dense USArray Transportable Array (TA) allows seismologists to observe the structure-induced evolution of the teleseismic wavefield across a large network in unprecedented detail. While Helmholtz tomography utilizes the amplitude and phase of one-component surface wave waveforms, the evolution of surface wave particle motion provides complementary constraints on small-scale heterogeneity beneath North America. While arrival angles support phase-based dispersion analyses of the mantle, observables such as the dip and the ZH ratio are particularly useful to constrain shallow crustal layers. This project will provide a new database of surface-wave particle motion observable.A second aspect of this project focuses on Rayleigh wave azimuthal anisotropy. The dense station spacing of the TA allows a leap-frogging "beam forming" type approach using small subarrays. In comparison to an all-inclusive tomographic joint inversion scheme for anisotropy and heterogeneity, this approach can remove some of the trade-offs between the two. The underlying assumption here is that structure within a subarray is homogeneous, but given the dense station spacing of the TA, this should be a valid assumption. In return, obtained observables will be "in-situ".

USAray可移动阵列（TA）的部署使地震学家能够以前所未有的细节编辑地震数据集和图像。迄今为止，对大约2000个台站的极其丰富的数据集进行的地震分析是基于“标准”地震数据，如走时。然而，其他类型的数据，如表面波的粒子运动，提供了补充观测，以模拟浅层地球结构中更小的细节。TA台站之间的短距离使地震学家能够详细地追踪来自遥远地震的表面波在穿越TA时是如何弯曲的。这反过来又可以用来微调北美地下的地球结构模型，并提高科学家对该大陆是如何构成的理解。某些地幔岩石表现出地震各向异性，地震波传播的速度取决于它们接近的方向。各向异性也形成于板块，如北美板块，对沿其边缘沿着的力作出反应。TA站的小子集可以像天线一样用于测量该各向异性的性质。这反过来又使科学家能够探索形成、移动并最终摧毁地球板块的地幔过程。在全球层析成像研究中，表面波到达角已被证明对增强短波长结构的成像极为有用。由于全球地震网络稀疏，对这些数据的解释是用摄动理论的大圆方法来解释的。密集的USAray可移动阵列（TA）使地震学家能够以前所未有的细节观察大型网络中结构引起的地震波场演化。虽然亥姆霍兹层析成像利用单分量地波波形的振幅和相位，但地波粒子运动的演变对北美地下的小规模非均匀性提供了补充约束。虽然到达角支持地幔的基于相位的色散分析，但诸如倾角和ZH比之类的可观测量对于约束地壳浅层特别有用。本计画将提供一个新的可观测面波质点运动资料库。本计画的第二个方面则集中在瑞雷波方位各向异性。TA的密集站间距允许使用小型子阵列的蛙跳式“波束形成”型方法。与各向异性和非均匀性的全包式层析联合反演方案相比，这种方法可以消除两者之间的一些权衡。这里的基本假设是子阵列内的结构是均匀的，但是考虑到TA的密集站间距，这应该是一个有效的假设。作为回报，获得的观测值将是“原位”的。