In-situ characterization of the lithosphere-asthenosphere system beneath NW Pacific Ocean via broadband dispersion survey with two OBS array
In-situ characterization of the lithosphere-asthenosphere system beneath NW Pacific Ocean via broadband dispersion survey with two OBS array
复制标题
通过两个 OBS 阵列宽带色散调查对西北太平洋下方的岩石圈-软流圈系统进行原位表征
DOI：
10.1029/2018gc007588
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发表时间：
2018
期刊：
影响因子：
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通讯作者：
H. Utada
中科院分区：
文献类型：
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作者：
Takeo;A.;H. Kawakatsu;T. Isse;K. Nishida;H. Shiobara;H. Sugioka;A. Ito;H. Utada
我们在西北太平洋海底布设了两个宽带海底地震仪阵列，在130和140 Ma的海底年龄进行了宽带频散调查。通过结合环境噪声和地震面波分析，获得了周期范围为5-100 s的瑞利波频散曲线，然后用于反演每个阵列下方的一维各向同性和方位各向异性βV（VSV）剖面。所获得的剖面显示，尽管海底年龄差异很小，水平距离约为1，000 km，但在80-150 km深度范围内，低速带（LVZ）的各向同性βVin差异约为2%。热模型的前向色散曲线计算表明，简单的冷却模型不能解释观察到的差异，需要一个额外的机制，如岩石圈下的小尺度对流。此外，方位各向异性的最快方位角在LVZ显着偏离当前板块运动方向。我们推断，这些观测结果与研究区域下方存在的小规模对流一致。至于Lid中的方位角各向异性，在从Moho到~40 km的深度处，峰-峰强度为3-4%。最快的方向在130 Ma时在A区几乎垂直于磁线理，在140 Ma时在B区倾斜于磁线理，表明在三个脊轴包围下的新生太平洋板块之下存在复杂的地幔流动。LVZ中的方位各向异性的强度为~ 2%，表明径向各向异性比方位各向异性更强。
We conducted broadband dispersion survey by deploying two arrays of broadband ocean bottom seismometers in the northwestern Pacific Ocean at seafloor ages of 130 and 140 Ma. By combining ambient noise and teleseismic surface wave analyses, dispersion curves of Rayleigh waves were obtained at a period range of 5–100 s and then used to invert for one‐dimensional isotropic and azimuthally anisotropicβV(VSV) profiles beneath each array. The obtained profiles show ~2% difference in isotropicβVin the low‐velocity zone (LVZ) at a depth range of 80–150 km in spite of the small difference in seafloor ages and the horizontal distance of ~1,000 km. Forward dispersion‐curve calculation for thermal models indicates that simple cooling models cannot explain the observed difference and an additional mechanism, such as sublithospheric small‐scale convection, is required. In addition, the fastest azimuths of azimuthal anisotropy in the LVZ significantly deviate from the current plate motion direction. We infer that these observations are consistent with the presence of small‐scale convection beneath the study area. As for azimuthal anisotropy in the Lid, the peak‐to‐peak intensity is 3–4% at the depth from Moho to ~40 km. The fastest direction is almost perpendicular to magnetic lineation in area A at 130 Ma and oblique to magnetic lineations in area B at 140 Ma, suggesting complex mantle flow beneath the infant Pacific Plate surrounded by three ridge axes. The intensity of azimuthal anisotropy in the LVZ is ~2%, indicating that radial anisotropy is stronger than azimuthal anisotropy therein.