同震地表破裂及活动断层迹线的几何形貌特征

GEOMETRIC CHARATERISTICS OF CO-SEISMIC SURFACE RUPTURES AND ACTIVE FAULTS

天然断层面的几何形貌特征中隐含着大量与断层演化和破裂机制相关的信息,准确描述断层面的形貌特征对于认识断层的形成与发展,及其破裂过程具有重要意义。文中运用能谱密度分析方法,对全球52条同震地表破裂和300条活动断层的地表迹线数据进行分析和归纳,结果显示:1)它们的平均能谱密度曲线在频域上具有明显的3分段特征。在低频域,能谱密度曲线特征表征了km级以上尺度的构造块体边界的形貌特征;在中频域,则受到hm—km级尺度上的断层横向扩展、次级断裂的贯通以及地形因素的控制;在hm尺度上的拐点代表了重采样的有效长度,在hm级以下尺度的高频域,能谱曲线特征受到数据插值方法的控制;2)在km级以下尺度,同震地表破裂的能谱密度曲线显示3种破裂类型的断层迹线粗糙度之间存在明显差异:逆冲型>正断型>走滑型,这表明在该尺度范围内的破裂迹线几何形貌特征差异主要受破裂类型的控制;3)与同震地表破裂相比,活动断层迹线的能谱密度明显偏低。这表明随着破裂次数增加、断层活动历史增长,断层的粗糙度会逐渐减小,即粗糙度与成熟程度成反比。

Fault traces contain abundant information associated with the fracture process and mechanism,so an accurate and quantitative description of their geometric characteristics is of great significance to perceiving the generation and development of faults. We collected 52 co-seismic surface ruptures and300 active fault traces from across the whorld to analyse their geometric characteristics by the method of power spectrum density. Our results show that( 1) the average power spectrum density has a distinct three-segment charateristic in the frequency domain. In the low frequency domain it represents the geometric characteristics of the boundary of tectonic block. In the medium frequency domain,the power spectrum density reflects the processes of lateral growth and connection of secondary faults,and the turn point on the 100 meter scale represents the effective resampling length,below which the power spectrum density characteristics are meaningless.( 2) In the middle and high frequency domains,the power spectrum density curves of co-seismic surface ruptures show that there are obvious differences in roughness among three fault types,i.e. reverse>normal>strike-slip,which indicates that the geometric characteristics of co-seismic surface ruptures are controlled by the fault types.( 3)Compared with co-seismic surface ruptures,active fault traces have much lower power spectrum density,indicating the roughness of active fault traces becomes lower with increasing numbers of rupturing events and the lengths of active history,i. e.,the fault roughness is inversly proportional to its maturity.