Imaging Rayleigh wave attenuation with USArray
Imaging Rayleigh wave attenuation with USArray
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DOI：
10.1093/gji/ggw151
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发表时间：
2016-07-01
影响因子：
2.8
通讯作者：
Shen, Yang
中科院分区：
文献类型：
--
作者：
Bao, Xueyang;Dalton, Colleen A.;Shen, Yang
地球望远镜阵列提供了一个以前所未有的规模获取大陆上地幔的详细图像的机会。到目前为止，从美国阵列数据得到的大多数地幔模型包含地震波速度的空间变化；然而，在许多情况下，这些数据集本身并不允许进行非唯一的解释。地震衰减和速度模型的联合解释可以改进仅基于速度的解释，并提供对地幔的温度、成分、熔体含量和挥发分含量的重要约束。限制上地幔衰减的面波振幅除了衰减外，还受震源激发、弹性构造的聚焦和散焦以及局部场地放大等因素的影响。由于很难将衰减与这些其他因素分开，因此对北美上地幔的衰减结构知之甚少。在这项研究中，用站间互相关技术测量了S 25-100周期内瑞雷波的走时和振幅，该技术利用了邻近台站的波形相似性。在每个周期产生几个瑞雷波衰减和场地放大的估计，使用不同的方法来区分衰减和局部场地放大对幅度的影响。假设聚焦和散焦效应可以用旅行时间场的拉普拉斯来描述。所有方法都确定了相同的大范围衰减模式，包括衰减值可能被未建模的聚焦和散焦效应污染的区域。在去除污染衰减值后，建立了区域平均衰减图，并对这些瑞雷波衰减图所反映的本征剪切衰减的变化进行了探讨。
The EarthScope USArray provides an opportunity to obtain detailed images of the continental upper mantle at an unprecedented scale. The majority of mantle models derived from USArray data to date contain spatial variations in seismic-wave speed; however, in many cases these data sets do not by themselves allow a non-unique interpretation. Joint interpretation of seismic attenuation and velocity models can improve upon the interpretations based only on velocity and provide important constraints on the temperature, composition, melt content, and volatile content of the mantle. The surface wave amplitudes that constrain upper-mantle attenuation are sensitive to factors in addition to attenuation, including the earthquake source excitation, focusing and defocusing by elastic structure, and local site amplification. Because of the difficulty of isolating attenuation from these other factors, little is known about the attenuation structure of the North American upper mantle. In this study, Rayleigh wave traveltime and amplitude in the period range 25-100 s are measured using an interstation cross-correlation technique, which takes advantage of waveform similarity at nearby stations. Several estimates of Rayleigh wave attenuation and site amplification are generated at each period, using different approaches to separate the effects of attenuation and local site amplification on amplitude. It is assumed that focusing and defocusing effects can be described by the Laplacian of the traveltime field. All approaches identify the same large-scale patterns in attenuation, including areas where the attenuation values are likely contaminated by unmodelled focusing and defocusing effects. Regionally averaged attenuation maps are constructed after removal of the contaminated attenuation values, and the variations in intrinsic shear attenuation that are suggested by these Rayleigh wave attenuation maps are explored.