断层崖演化与古地震研究

DEGRADATION OF FAULT SCARP AND PALEOEARTHQUAKE RESEARCH

从断层崖演化模型及其理论分析入手 ,给出了模型的数学分析解 ,导出了一次突发事件和蠕动成因断层崖演化的等时地形 (地层 )线、最大坡度和崖下堆积体截面积的精确表达式 ,据此分析了可能造成的几何与沉积构造特征。根据野外观察、实验分析及理论研究 ,探讨了断层崖演化及其古地震学研究的一些重要问题 ,提出了与断层崖相关的古地震几何形态、沉积结构和实验分析的综合标志 ,并具体研究和确定了与红果子贺兰山东麓断层崖和孟家湾F2 0 1断层崖相关的 8次古地震事件及其近地表特征和复发周期 ,前者为 2 .0～ 3.0ka,平均 2 .4ka ,后者为 3.3～ 4 .0ka ,平均 3.6ka。

This paper deals with the degradation of fault scarp and the identification of paleo-earthquake in the light of theoretical and mathematical analysis of scarp development processes. We propose some models for fault scarp degradation in unstable and diffusion stages, and give out their mathematical solutions. From these solutions, the quantitative relation between geometrical features and/or sedimentary structures of fault scarp is analyzed. Furthermore, the precise expressions of the isochronous form-line of the scarp profile, the maximum gradient of scarp, and the sectional area of scarp deposits are established quantitatively for the use of paleo-earthquake research. Based on the field investigation, as well as experimental and mathematical analysis, the comprehensive indicators for identifying paleo-earthquakes associated with fault scarp, including geometrical, sedimentary, structural and experimental features, are summarized. Case studies on the fault scarp of the eastern Helanshan Fault at Hongguozi and fault scarp of the F 201 Fault at Mengjiawan were carried out. The results of these two studies reveal 2 series of 4 paleo-earthquake events that had occurred on the two faults respectively. The characteristics and recurrence intervals of these events have been studied in details. It is determined that the recurrence interval of paleo-earthquke events on the eastern Helashan Fault is 2.2～2.6ka, and that on the F 201 Fault is 3.3～4.0ka.