摘要
在地质调查的基础上，初步厘定了清江下游主要活动断层的现今几何轨迹结构，并从几何形态、结构特性和现今活动性三方面对其进行自然段划分；进而利用分形分维分析，估算活动断层不同区段轨迹结构的分维值。计算结果表明：每一个断层段具有一个特征性的分维值，轨迹结构越复杂，分维值越高，现今活动性越强；其中，仙女山断层带中段分维值最高， Ｄ＝ １２５７，而松园坪断层北段最低， Ｄ＝ １０１８。结合地震活动分析发现：仙女山断层带是清江下游现今活动最强的活动断裂；仙女山断层带的中小地震活动，具有间歇式 分段振荡迁移的特性；时间上地震活动期为１～５ａ，相对平静期为１０ａ 左右；空间上地震活动从南段开始，振荡迁移到北段，然后又向中段迁移，目前地震活动似乎正在向中南段边界迁移；并且，中南段断裂轨迹结构比北段复杂，分维值也高，地震活动强度相对较大，因此，未来仙女山断层带可能发生的中强地震（ Ｍｓ＝ ５０ 级左右）将主要集中于中南段，而不是北段。
The trace pattern of the main active faults in the low Qingjiang river has been measured on the basis of the geological investigation over the past five years.The trace pattern is characterized by the segmentation derived from discontinuity in fault geometric shape,structure and present acivity.For example,the Xiannushan fault trace is defined by 3 straight line segments.Fractal analysis of the fault trace pattern of the area shows that every segment has a characteristic slope value in the boxcounting curve,and the more complex is the trace pattern of some segment,the larger its fractal dimension value.Of them,the middle segment of the Xiannushan fault is characterized by the largest fractal dimension of D =1.257,whereas northern segment of the Songyuanping fault is characterized by the lowest fractal dimension of D =1.018 in the area.According to the seismic data of the area over the past about 40 years,the temporalspatial distribution of midsmall size earthquakes along the xiannushan fault is characterized by the intermitenceoscillating changes from one segment to another;in the temporal distribution,an earthquake active period is 1～5years,whereas an earthquake quiet period is about 10 years;in the spatial distribution,the earthquake occurred first in the northern segment,and then removed from the northern segment to the middle segment,and at present is likely removing toward the boundary between the middle and southern segment. By comparison,we found that the trace pattern of the midsouthern segment is more complicated,fractal dimension is large,and earthquake active size is larger than of the northern segment of the Xiannushan fault.Hence we suggest that,in a given tectonic setting,middlesize earthquakes that may occur along the Xiannushan fault will mainly concentrate on the midsouthern segment,and not on the northern segment in the future.
出处
《长春科技大学学报》
CSCD
1999年第3期272-278,共7页
Journal of Changchun University of Science and Technology
基金
国家自然科学基金
地质力学开放研究实验室资助
长江三峡勘测院委托项目
