鲜水河断裂带南北构造差异性的地球物理分析

Geophysical analysis on the tectonic difference between northern and southern segments of Xianshuihe fault zone

  • 摘要: 对鲜水河断裂带重磁异常进行向上延拓,通过计算观测面高度异常与延拓后异常之间的相关系数得出最佳向上延拓高度,该延拓高度所对应的延拓结果即为研究区构造背景产生的异常值。向上延拓结果显示布格重力异常值沿鲜水河断裂带自北西向南东逐渐增大,反映出下地壳底边界沿该方向呈升高趋势,可能由青藏高原地壳软弱物质 “东向逃逸” 所致。化极后ΔT磁异常延拓结果表明鲜水河断裂带南东段的康定—石棉以东为强磁性刚性基底。以鲜水河断裂带为分界的不同地块之间基底岩石及地层物性的不同是断裂带南北磁性差异的主导原因。对鲜水河断裂带两侧各约50 km范围内地震的震源深度进行统计,经投影至剖面及线性拟合求出鲜水河断裂带的三维几何形状。结果表明鲜水河断裂带总体倾向南西,倾角近乎直立,范围约为57°—88°。

     

    Abstract: Xianshuihe fault zone is one of the strongly active seismic belts in the eastern margin of Tibetan Plateau, with the features of large scale, high activity and seismic frequency. Four M≥7.0 earthquakes have occurred along Xianshuihe fault zone. It is indicated that the differences of geometry features, activity characteristics and intensity, surface rupture characteristics of earthquakes exist between northern and southern segments of Xianshuihe fault zone. The upward continuation result of gravity-magnetic anomaly in Xianshuihe fault zone is present. The optimum upward continuation height is determined by calculating correlation coefficient of anomaly at observed surface height and upward continuation height. The upward continuation result at this height is corresponding to the anomaly caused by structural setting. It shows that the bottom of lower crust is on the rise from NW to SE according to the consecutive increase of Bouguer gravity anomaly at such orientation along the fault, which probably results from eastward motion of crustal soft material in Tibetan Plateau area. Magnetic anomaly reduced to the pole reveals that there is strongly magnetic rigid base to east of Kangding-Shimian in the southern segment of Xianshuihe fault zone. The difference in physical property of basement rocks and stratum in different blocks bounded by Xianshuihe fault zone is the major reason for magnetic diversity between northern and southern segments of the fault zone. With the statistical results of focal depths of seismic events in the range of 50 kilometers on both sides of the fault zone, its three-dimensional geometry is determined by projection and linear fitting. It is indicated that the dip direction of Xianshuihe fault zone is SW and its dip angle is almost vertical in the range of 57° to 88°.

     

/

返回文章
返回