Crustal shear wave velocity structure of the western United States inferred from ambient seismic noise and earthquake data
Crustal shear wave velocity structure of the western United States inferred from ambient seismic noise and earthquake data
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DOI：
10.1029/2010jb007448
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发表时间：
2010-10
影响因子：
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通讯作者：
M. Moschetti;M. Moschetti;M. Ritzwoller;F. Lin;Yingjie Yang
中科院分区：
文献类型：
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作者：
M. Moschetti;M. Moschetti;M. Ritzwoller;F. Lin;Yingjie Yang
[1]面波频散测量从环境地震噪声和阵列为基础的测量从EarthScope/USAray便携式阵列（TA）观测到的地震波的反演使用蒙特卡洛方法的3-D VS模型的地壳和上地幔下的美国西部。这些方法的数据组合产生了异常宽频带的频散信息，从6到100秒的周期，这限制了地壳和上地幔的剪切波速度结构，深度超过100公里。TA网络产生的高横向分辨率和色散信息的宽带性激发了3-D模型的适当参数化问题，特别是模型的地壳部分。我们发现，一个相对简单的模型，其中VS单调增加的深度在地壳中可以很好地拟合数据超过90%的研究区域，除了在8个离散的地区，更大的地壳复杂性显然存在。地壳复杂程度较高的地区有奥林匹克半岛、门多西诺三联点、亚基马褶皱带、南部卡斯卡迪亚后弧、加州的大中央谷、索尔顿海槽、斯内克河平原和瓦萨奇山脉。我们还表明，一个强大的Rayleigh-Love的差异存在于美国西部的大部分地区，这可以通过引入径向各向异性在地幔和特别是地壳解决。我们集中我们的分析证明地壳径向各向异性的存在，并主要讨论了地壳部分的各向同性模型，结果从径向各向异性模型的Voigt平均。蒙特卡罗反演的模型不确定性用于识别模型中稳健的各向同性特征。美国西部下地幔上部主要由四个大尺度剪切波速度特征组成，但下地壳速度结构表现出更大的不均匀性。我们认为，这些下地壳结构主要是由与上地幔的相互作用，包括侵入和底侵的镁铁质地幔物质和热抑郁的波速从地幔的传导加热所造成的。中地壳和上地壳的波速一般是相关的，并推断显着的异常是由于大陆边缘的火山岩增生和火山侵入。
[1] Surface wave dispersion measurements from ambient seismic noise and array-based measurements from teleseismic earthquakes observed with the EarthScope/USArray Transportable Array (TA) are inverted using a Monte Carlo method for a 3-D VS model of the crust and uppermost mantle beneath the western United States. The combination of data from these methods produces exceptionally broadband dispersion information from 6 to 100 s period, which constrains shear wave velocity structures in the crust and uppermost mantle to a depth of more than 100 km. The high lateral resolution produced by the TA network and the broadbandedness of the dispersion information motivate the question of the appropriate parameterization for a 3-D model, particularly for the crustal part of the model. We show that a relatively simple model in which VS increases monotonically with depth in the crust can fit the data well across more than 90% of the study region, except in eight discrete areas where greater crustal complexity apparently exists. The regions of greater crustal complexity are the Olympic Peninsula, the MendocinoTriple Junction, the Yakima Fold Belt, the southern Cascadia back arc, the Great Central Valley of California, the Salton Trough, the Snake River Plain, and the Wasatch Mountains. We also show that a strong Rayleigh-Love discrepancy exists across much of the western United States, which can be resolved by introducing radial anisotropy in both the mantle and notably the crust. We focus our analysis on demonstrating the existence of crustal radial anisotropy and primarily discuss the crustal part of the isotropic model that results from the radially anisotropic model by Voigt averaging. Model uncertainties from the Monte Carlo inversion are used to identify robust isotropic features in the model. The uppermost mantle beneath the western United States is principally composed of four large-scale shear wave velocity features, but lower crustal velocity structure exhibits far greater heterogeneity. We argue that these lower crustal structures are predominantly caused by interactions with the uppermost mantle, including the intrusion and underplating of mafic mantle materials and the thermal depression of wave speeds caused by conductive heating from the mantle. Upper and middle crustal wave speeds are generally correlated, and notable anomalies are inferred to result from terrane accretion at the continental margin and volcanic intrusions.