摘要
为了调查羌塘盆地中部壳内低速层分布特征,对布设在羌塘盆地的TITAN-I宽频带地震台站所记录的远震波形数据进行接收函数分析,并引入时频域相位滤波技术改善接收函数信噪比,反演得到各台站下方100 km深度范围内的一维S波速度结构.结果表明,时频域相位滤波方法能够显著提高信噪比;羌塘盆地Moho深度为58±6 km,具有较高的泊松比值;中下地壳壳内低速层广泛分布,横向不连续,埋深在20～30 km,层厚6～12 km,剪切波速度为3.4±0.1 km/s;部分地区在埋深为10 km的中上地壳存在一层厚约4 km的低速薄层.羌塘盆地中下地壳壳内低速层是由于上涌的深部软流圈物质与下地壳发生大范围的接触,造成壳内及上地幔部分熔融引起的.
In order to investigate the distribution characteristics of the low velocity layer in the central Qiangtang basin,this study conducted the TITAN-I teleseismic receiver functions across the Qiangtang basin. And the signal-to-noise ratio of the receiver function was improved by the phase filtering technique in the time frequency domain. Finally,the one-dimensional S wave velocity structure in the depth of 100 km below each station is obtained by the nonlinear inversion of conjugate gradients algorithm for the complex spectrum ratios of receiver function. The results show that the phase filtering method in the time frequency domain can significantly improve the signal-to-noise ratio and make the one-dimensional S wave velocity structure of the subsequent inversion more reliable. The Moho depth of the Qiangtang basin is 58 ±6 km,and where has a higher Poisson's ratio. The low velocity layer in the mid-lower crust is widely distributed. The transverse discontinuity is discontinuous,and the depth is between 20 and 30 km,the thickness of the layer is 6-12 km,the shear wave velocity is 3.4± 0.1 km/s. In some areas,there is a thin layer of 4 km thin layer in the mid-upper crust with a depth of 10 km. The low velocity layer in the mid-lower crust of the Qiangtang basin is caused by the deep mantle derived magma upwelling along the tectonic weak zone,resulting in partial melting in the mid-lower crust and upper mantle.