太康隆起南缘新郑-太康断裂的新生代活动形迹与地震活动

THE CENOZOIC TECTONICS AND SEISMIC ACTIVITY OF XINZHENG-TAIKANG FAULT IN THE SOUTHERN EDGE OF TAIKANG AREA

在对比分析太康地区7个钻孔的新近纪地层及其底界基础上,对101条共4 991km长的浅层地震剖面进行了追踪解释,结果显示:沿太康隆起南缘新郑市—太康县一带发育1条新生代活动的区域性隐伏断裂,控制着太康隆起与周口凹陷的分界,可称为新郑-太康断裂。该断裂由东、西2支组成。西支断裂总体走向NW,断面NE倾,长度超过140km;东支断裂走向NW-NEE,断面倾向SW-SSE,长约50km。2条支断裂均断错了新近系的底界,局部向上延伸至第四系。断裂东、西2支的叠合地带可能为应力累积区,现代地震主要发生在这一部位。

On the basis of dividing and comparison of the Neogene strata and their bottoms revealed by 7 drill holes in Taikang area, we completed 101 seismic profiles with a total length of 4 991km. Seismic data were compared and interpreted. The results indicate that Xinzheng-Taikang Fault, as a blind fault extending from Xinzheng to Taikang, which was considered as an EW striking fault from Xuchang to Taikang before, is the boundary of Taikang uplift and Zhoukou depression, controlling the sedimentation since Neogene Period. So we named the fault the Xinzheng-Taikang Fault, which is composed of two branches, mainly, the east and west branches. The west branch strikes northwest, dipping northeast with steep angles, and the fault plane extending more than 140km in length. As revealed on the seismic profiles, the eastern segment of the west branch is normal fault, while the west segment of the branch shows characteristics of strike-slip fault. The east branch trends NW-- NEE, dipping SW--SSE with the length of about 50km. Two branches form a minus flower structure, indicating the strike slip-extension tectonic background. The bottom of Neogene strata is offset about 120m by the east branch, 20m by the west branch, and the bottom of Quaternary is probably offset too. Meanwhile, latest studies suggest that the composite strip of the two branches of Xinzheng- Taikang Fault, which is a tectonic transfer zone, is the subduction zone between the two strike-slip faults. The tectonic stress tends to be released by the east-west branch fault, and the zone should be the seismogenic structure for the recent seismicity in Taikang area. In 2010, the latest earthquake of Ms4.7 occurred in this area, causing 12 people wounded. The seismogenic structure was considered to be the Xinzheng-Taikang Fault. So locating the fault exactly is of great importance to disaster prevention.