Ambient noise tomography across the Cascadia subduction zone using dense linear seismic arrays and double beamforming
Ambient noise tomography across the Cascadia subduction zone using dense linear seismic arrays and double beamforming
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DOI：
10.1093/gji/ggz109
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发表时间：
2019-06
影响因子：
2.8
通讯作者：
Yadong Wang;F. Lin;K. Ward
中科院分区：
文献类型：
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作者：
Yadong Wang;F. Lin;K. Ward
在2017年夏天，我们部署了174个三分量节点检波器沿着130公里的东西线横跨中部俄勒冈州的前弧持续约40天。我们的目标是评估的可能性成像的岩石圈结构的细节与密集，但持续时间短的被动地震信号采样。在这项研究中，我们使用被动记录的节点阵列和以前的CASC 93宽带阵列沿着同一条线来计算噪声互相关。在3至15 s周期之间的互相关中观察到基本Rayleigh波信号。为了增强信号并同时测量相速度，我们采用了双波束形成方法。在每个周期和位置，选择一个源波束和一个接收器波束，并基于假定的局部速度移动和堆叠两者之间的互相关。一个2-D网格搜索，然后用来找到最好的速度在源和接收器的位置。通过使用不同的源和接收器对，在每个位置获得多个速度测量值，并使用平均值和平均值的标准差确定每个位置的最终速度和不确定性。所有可用的相速度在整个配置文件，然后用于反演的2-D剪切波地壳速度模型。在威拉米特山谷内的沉积物中观察到了分辨率很好的浅层低速异常，在中下地壳中观察到了可能与Siletzia盆地有关的快速异常。我们证明了环境噪声双波束形成方法是一种有效的工具，通过密集和大规模（>100公里）的临时地震台阵成像详细的岩石圈结构。
In the summer of 2017, we deployed 174 three-component nodal geophones along a 130 km west–east line across the central Oregon forearc lasting about 40 d. Our goal was to evaluate the possibility of imaging the lithospheric structure in detail with a dense but short-duration sampling of passive seismic signals. In this study, we used passive recordings from the nodal array and the previous CASC93 broad-band array along the same line to calculate noise cross-correlations. Fundamental Rayleigh wave signals were observed in the cross-correlations between 3 and 15 s period. To enhance the signal and simultaneously measure the phase velocity, we employed a double beamforming method. At each period and location, a source beam and a receiver beam were selected and the cross-correlations between the two were shifted and stacked based on the presumed local velocities. A 2-D grid search was then used to find the best velocities at the source and receiver location. Multiple velocity measurements were obtained at each location by using different source and receiver pairs, and the final velocity and uncertainty at each location were determined using the mean and the standard deviation of the mean. All available phase velocities across the profile were then used to invert for a 2-D shear wave crustal velocity model. Well resolved shallow slow velocity anomalies are observed corresponding to the sediments within the Willamette Valley, and fast velocity anomalies are observed in the mid-to-lower crust likely associated with the Siletzia terrane. We demonstrate that the ambient noise double beamforming method is an effective tool to image detailed lithospheric structures across a dense and large-scale (>100 km) temporary seismic array.