Late Quaternary Activity of the Chuxiong-Nanhua Fault and the 1680 Chuxiong Ms6 3/4 Earthquake

In this paper,according to the results of the satellite imagery interpretation and field investigation,we study the active features and the latest active times of the ChuxiongNanhua fault,the Quaternary basins formation mechanism,and the relationship between the fault and the 1680 Chuxiong M_S6 3/4earthquake. Several Quaternary profiles at Lvhe,Nanhua reveal that the fault has offset the late Pleistocene deposits of the T2 and T3 terraces of Longchuan river, indicating that the fault was obviously active in late Quaternary. The Chuxiong-Nanhua fault has been dominated by dextral strike slip motion in the late Quaternary,with an average rate of 1. 6-2. 0 mm/a. Several pull apart Quaternary basins of Chuxiong,Nanhua,and Ziwu etc. have developed along the fault.The 1680 Chuxiong M_S6 3/4earthquake and several moderate earthquakes have occurred near the fault. The Chuxiong-Nanhua fault are the seismogenic structure of those earthquakes,the latest fault movement was in the late-Pleistocene,and even the Holocene.In large area,the Chuxiong-Nanhua fault and the eastern Qujiang fault and the Shiping fault composed a set of NW-trending oblique orientation active faults,and the motion characteristics are all mainly dextral strike slip. The motion characteristics,like the red river fault of the Sichuan-Yunnan Rhombic Block southwestern boundary,are concerned with the escaping movement of the Sichuan-Yunnan Rhombic Block.

楚雄-南华断裂晚第四纪活动与1680年楚雄6 3/4级地震

根据卫星影像解译和野外调查结果，本文重点分析研究楚雄-南华断裂的活动特征、最新活动时代、第四纪盆地的成因以及与1680年楚雄6 3/4级地震的关系。吕合、南华等多处第四纪断层剖面揭示了断错龙川江Ⅱ、Ⅲ级阶地晚更新世晚期堆积，表明该断裂是一条晚第四纪活动断裂，其最新时代为晚更新世晚期乃至全新世，运动性质以右旋走滑运动为主，水平走滑速率1．6～2．0mm／a。沿断裂发育有楚雄、南华、子午等多个第四纪拉分盆地。历史上，断裂附近曾发生1680年楚雄6％级地震和多次中强地震，楚雄一南华断裂为这些地震的发震构造。从更大区域范围看，它与东部的曲江断裂、石屏一建水断裂一起，构成一组斜列的右旋走滑为主的活动断裂带。这种运动学特征类似于川滇菱形块体西南边界的红河断裂带，与川滇菱形块体SE向逃逸（运动）有关。

2003年云南大姚6.2和6.1级地震序列研究

2003年7月21日和10月16日,在云南省大姚县境内相继发生62和61级地震,微观震中分别为2595°N,10123°E和2592°N,10130°E;宏观震中分别位于大姚县城北约25km的昙华乡和20km的六苴乡,极震区烈度均为Ⅷ度。两次地震共造成19人死亡,600余人受伤,直接经济损失达100750万元。通过对这两次强震序列的时、空、强等特征进行分析认为①在大姚62级地震序列衰减后期呈现出一些“双震”的特征;②大姚61级地震序列的时空分布仍有异常显示;③大姚62,61级地震的发生是楚雄—南华地震带强震活动进一步向北延伸的表现。

1680年楚雄地震地表破裂遗迹及其震级讨论

1680年楚雄地震，造成楚雄州和南安州官署、寺庙、桥梁、学堂等重要建筑物几乎破坏殆尽，死亡近3000人。在航片解译的基础上，经仔细的野外调查以及白龙新村、上野马和大石碑3个探槽的开挖，在楚雄盆地西缘发现此次地震形成的地表破坏遗迹，包括地震断层、地震陡坎、地裂缝、砂脉、地震楔等，分布于上野马-尹家咀水库-上三村一线，总长约12km。地震陡坎高度0.6~1.5m，地震断层位错量0.2~1.2m；采集了19个14C样品进行AMS测年，得到断错的最新地层14C年龄为590±30a B.P.。据地表破裂规模和云南地区地震实例分析，此次地震的震级应在7级以上，宏观震中位于地表破裂非常集中的上野马-上三村一带。楚雄-南华断裂是川滇菱形块体内部一条重要的活动断裂，以右旋走滑兼逆冲运动为主，全新世有明显的活动迹象。此次地震等震线呈NW向展布并与楚雄-南华断裂走向基本一致，所揭示的地表破裂分布也与极震区相吻合，据此认为，1680年楚雄地震应是楚雄-南华断裂活动所致。