Shear wave velocity and radial anisotropy structures beneath the central Pacific from surface wave analysis of OBS records
Shear wave velocity and radial anisotropy structures beneath the central Pacific from surface wave analysis of OBS records
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DOI：
10.1016/j.epsl.2020.116086
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发表时间：
2020-03
影响因子：
5.3
通讯作者：
Xiaozhou Yang;Yinhe Luo;Hongrui Xu;K. Zhao
中科院分区：
文献类型：
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作者：
Xiaozhou Yang;Yinhe Luo;Hongrui Xu;K. Zhao
中太平洋板块远离俯冲带、地幔柱火山热点等动力学系统，经历了简单的大洋演化，是研究岩石圈-软流圈系统动力学的理想区域。在这项研究中，我们收集了三分量连续地震数据和差压计数据记录的15个宽带海底地震仪（OBS）从NoMelt实验。我们处理连续的地震噪声数据，以获得基本（6-30秒）和第一高（5-11秒）模式瑞利波和基本模式洛夫波（5-12秒）的相速度。本文采用双平面波方法对瑞利波进行了数值模拟，得到了周期为20-150 s的基模相速度;对瑞利Love波进行了高分辨率线性Radon变换，得到了周期为28-48 s的基模Love波相速度。然后，我们共同反演瑞利波和Love波的平均相速度，以构建从海底到NoMelt区域下方150 km深度的1-D各向同性剪切波速度和径向各向异性。我们的一维模型显示了一个低速区（LVZ）下的高速盖。通过比较我们的结果与部分熔融模型的预测，我们建议LVZ归因于存在少量的熔体在软流圈。在地壳中观察到强烈的径向各向异性（5-6%）。但地幔岩石圈具有弱的径向各向异性（< 1%），这与新洋板块形成过程中洋中脊角隅地幔流的历史相一致。在软流层中观察到了较强的径向各向异性（4-5%），这与全球面波层析成像结果和数值模拟研究结果相一致，反映了与大洋板块在下伏软流层上方运动有关的软流层强剪切应变。
The central Pacific plate is an ideal area to study the dynamics of the lithosphere-asthenosphere system, as this region is far away from other dynamics systems, such as subduction zones and volcanic hotspots of mantle plumes, and has experienced simple oceanic evolution. In this study, we collect three-component continuous seismic data and differential pressure gauge data recorded by 15 broadband ocean bottom seismometers (OBSs) from the NoMelt experiment. We process continuous seismic noise data to obtain phase velocities of the fundamental (6-30 s) and first high (5-11 s) mode Rayleigh waves and fundamental mode Love waves (5-12 s). We apply a two-plane-wave method to teleseismic Rayleigh waves to obtain the fundamental mode phase velocities at 20-150 s periods, and apply high-resolution linear Radon transform to teleseismic Love waves to obtain phase velocities for the fundamental mode Love waves at 28-48 s periods. Then, we jointly invert the average phase velocities of Rayleigh and Love waves to construct 1-D isotropic shear wave velocity and radial anisotropy from the seafloor to 150 km depth beneath the NoMelt region. Our 1-D model shows a low velocity zone (LVZ) beneath a high velocity lid. By comparing our results with the predictions of partial melt models, we suggest the LVZ is attributed to the presence of a small amount of melt in the asthenosphere. Strong radial anisotropy (5-6%) is observed in the crust. But the mantle lithosphere is characterized by weak radial anisotropy (< 1%), consistent with the corner mantle flow history at the mid-ocean ridge during the formation of new oceanic plates. Strong radial anisotropy (4-5%) is observed in the asthenosphere, which is consistent with the global surface wave tomography results and numerical simulation studies, reflecting the strong shear strain of asthenosphere related to the motion of oceanic plate over the underlying asthenosphere.