采用重力梯度多尺度分析方法揭示青藏高原岩石圈结构特征

Lithospheric structure feature of the Tibetan Plateau revealed by multi-scale analysis of gravity gradients

  • 摘要: 目前利用重力梯度数据反演岩石圈结构存在垂向识别能力不足的问题。为此,本文利用小波多尺度分析方法对青藏高原地区垂直重力梯度扰动进行分解,并采用功率谱分析方法估计了不同小波分解阶数重力梯度扰动的场源埋深,以获取不同深度处更为精细的结构特征。进一步,根据不同阶重力梯度扰动及其平均场源深度,提取青藏高原莫霍面产生的重力梯度扰动信号,反演莫霍面地形。重力梯度扰动小波分解结果表明:小于10 km深度的浅层物质所产生的垂直梯度扰动零散分布于区域边缘和中南部;深度在20 km-50 km范围内的物质所产生的垂直梯度扰动主要分布在中西部和中南部,闭圈逐渐扩大;在约60 km深的区域,存在大型密度异常体;处于70km深度以下的下地壳和上地幔区域,密度分布无明显特征。莫霍面反演结果表明:青藏高原莫霍面地形总体上呈西深东浅分布,平均深度约为48 km,最大深度约66 km,位于( 78°E,35°N);本文反演的青藏高原莫霍面地形与CRUST1.0模型提供的莫霍面地形两者的空间格局相似,且相关性( COFF)约为0.83;与控制点莫霍面深度对比,本文反演的莫霍面地形结果精度为8.81 km,优于CRUST1.0的11.40 km。

     

    Abstract: Objectives: The vertical resolution of crustal structure inverted by using gravity gradients needs to be improved at present. Method: This paper employs wavelet multi-scale analysis method to decompose the vertical gravity gradient data in the Tibetean Plateau, and uses power spectrum analysis method to estimate the field source depth of gravity gradient with different wavelet decomposition orders. Further, according to the average field source depth of gravity gradients of different orders, the gravity gradient signals generated by the Moho of the Tibetan Plateau are extracted to invert the Moho topography. Results: The more detailed structural features at different depths are obtained. Conclusions: The wavelet decomposition results of gravity gradient show that the vertical gradient of disturbance generated by shallow field source less than 10 km depth is scattered in the edge and south-central of the region. The vertical gradient of the disturbance generated by the middle-level field source with a depth of 20km-50km is mainly distributed in the central and southern regions, and the closed circle gradually expands. There are large density bodies in the region of about 60 km depth. In the lower crust and upper mantle below 70 km depth, the density distribution has no obvious characteristics. The inversion results of the Moho show that the terrain of the Moho in the Tibetan Plateau is generally deep in the west and shallow in the east, with an average depth of about 48 km and a maximum depth of about 66 km, located at (78 ° E, 35 ° N). The spatial pattern of the Moho terrain in the Tibetan Plateau is similar to that provided by the CRUST1.0 model, and the correlation (COFF) is about 0.83. Compared with the control point depths, the accuracy of the inverted Moho terrain result is 8.81 km, which is better than 11.4 km of CRUST1.0.

     

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