鲜水河-小江断裂系第四纪与红河断裂带交切关系研究

There are two different models about the recent tectonic dynamics in the southeast margin of Tibetan Plateau. Although the clockwise rotation deformation model is supported by GPS observation data, which shows that the sinistral strike-slip movement in the Xianshuihe-Xiaojiang fault system is transferred across the Red River fault zone, structural relationship is not clear and geological evidences are absent. Thus, precise study on the fault distribution and activity is crucial in differentiating the two different models. The field survey conducted in the recent, correlated with the interpretation of remote sensing, provides a basis to determine the several representative sections, including the intersection region of the southern segment of the Xiaojiang fault and the Red River fault zone, for studying at detail. Geological mapping with a large scale, such as 1:5,000～10,000, precise topographic measuring by equipments, such as the 3-D laser scanner (RIGELVZ-1000), trench detecting, systematic sampling and dating of the Quaternary deposits will be carried out at the representative sections. The purpose of the study is to acquire a complete and reliable understanding of active features about the two sets of faults in the Quaternary, which include deformation styles, distribution, slip rates and inception time. The above results, correlated with the latest results of deep tectonics, GPS data and seismology, may be applied to obligate or test the dynamic models about the southeast margin of Tibetan Plateau., which will be in favor of improving our recognitions of the seismotectonic environment. It can also provide a scientific basis for assessing the seismic hazards and resisting standards. The project has both theoretical and practical meanings.

青藏高原东南缘主要有两种不同的现今构造动力学模型，尽管其中的顺时针转动变形模型得到了GPS观测资料佐证，显示了鲜水河-小江断裂系左旋走滑运动对红河断裂带的切穿，但一直缺少明确的构造联系。本项目拟在已开展的研究基础上，结合高分辨率遥感影像的解译，在小江断裂带南段与红河断裂带交汇区及其邻近有代表性地段，借助大比例尺地质填图、精细地貌测量、槽探和系统的新年代测定等工作，围绕两组断裂第四纪时期构造变形特征、分布状况、运动参数及发生时代开展研究；结合元江断裂和个旧断裂活动性调查，厘定鲜水河-小江断裂系第四纪与红河断裂带交切关系及其方式。通过与深部构造、GPS观测资料和地震学等最新研究成果的综合分析，对青藏高原东南缘现今构造动力学理论模型进行约束和检验，深化对地震构造环境特征的认识，为合理评价我国西南、华南以及东南亚地区地震危险性与抗震设防标准提供科学基础。本项申请具有重要的理论意义和社会价值。

青藏高原东南缘晚第四纪正在形成一个新生活动构造系统，其中最重要的突破有可能是鲜水河-小江断裂系对红河断裂的切穿，与分布在该断裂系西南的北东向断裂一起，构成了一条左旋走滑边界带。本项目通过在红河断裂两侧沿着北东向断裂走向上1:1万的追踪式调查，发现红河南边的绿春-江城断裂存在断错晚第四纪地层的地质证据，并且这种地质证据向北东可以追踪到红河边，与红河北侧的小江断裂南段在较窄的范围内相衔接。最晚一次活动的测年结果为距今970-1347 yr BP。红河断裂在交汇区两侧、即中段和东段的活动性质、最晚活动时代均存在明显不同。红河断裂中段晚第四纪表现为正-走滑运动性质，从地质上证实了项目组先前根据地震学研究提出的“滇东南弧形构造带现今很可能处于一个张-剪性动力学环境”的认识。.基于机载LIDAR测量生成的三维数字地形，采用LaDiCaoz_v2软件，获得了北东向绿春-江城断裂上3条冲沟的同步最大左旋位错量为85.2±15.4m，冲沟下切并被左旋断错的起始时间为25.4±2.4 ka。在先前给出的红河北边小江断裂南段左旋走滑速率(7.02±0.20) mm/yr基础上，本项目得到了红河南边绿春-江城断裂左旋走滑速率为(3.44±0.93) mm/yr。本项目查明了鲜水河-红河断裂系不是以弥散式的方式、而是在一个较窄的范围内切穿了红河断裂带。在切穿红河断裂之后，沿着鲜水河-小江断裂系的北东向构造变形分散到一组成帚状分布的北东、北北东或北东东向断裂上，而不是单一的断裂继续向西南延伸。在青藏高原东北缘现今构造活动中，鲜水河-小江断裂系起着主导性作用；但北西向红河断裂的存在也构成了鲜水河-小江断裂系分段活动的一个重要边界。.在地震危险性分析方面，小江断裂南段大震复发时间上不规则，但在位错量、即震级上表现出特征滑动模式。对1606年建水地震的复核结果表明：此次地震不但触发较大规模的滑坡，并且一些滑坡的发育与此次地震的地表破裂带密切相关，震级应≥7.5级。因此，可以认为鲜水河-小江断裂系的强烈活动性和大震发生能力至少一直延续到小江断裂南段。