Abstract:

Active faults refer to faults that have been active since the late Quaternary(100000~12 0^{}000 years)which are the culprits of large earthquakes. They can be divided into Holocene faults and Late Pleistocene faults. The Holocene fault is the active fault that has displaced on or near the surface in the past 10000 years. The Active faults may cause seismic surface dislocation in the future, which will damage the project crossing the active fault. It is necessary to take measures to avoid or resist the fault. Therefore, finding out the distributions of active faults are the prerequisite for reducing earthquake disaster losses and disaster risks.

We undertook the compilation of the 1︰1000000 seismotectonic map of Tibet in the first national comprehensive risk survey of natural disasters. The preparation of a seismotectonic map is to conduct detailed investigation and research on active faults within the research scope, including large-scale active faults with a strong earthquake-generating capacity, as well as small-scale and highly active faults. The Qinghai-Tibetan plateau is a typical strong earthquake-prone area with wide distribution, high frequency, high intensity and shallow source of seismicity. This study introduces the Holocene active faults in the modified scale(I45)of 1︰1000000 international standard topographic map.

We use Satellite remote sensing images to determine the locations of the faults, identify their characteristics, and assess the ages of their latest activity and quantitative parameters such as intensity. Satellite remote sensing interpretation is the most important method to study active faults. This is especially true in the Qinghai-Tibetan plateau region, where active fault traces are clear and lack overlying Quaternary layers. High-resolution satellite remote sensing images can capture various tectonic and geomorphological phenomena formed by fault activity.

In the study area, we interpreted Six Holocene active faults by using high-resolution satellite images, including the MargaiCaka fault, the Riganpeicuo fault, the Yibuchaka graben, the Qingwahu fault, the Dongcha fault, and the central part of Qixiangcuo fault. When analyzing each fault, typical images with evidence of active faults are intercepted, and the typical remote-sensing image features of active faults are summarized. It is clear that the typical remote sensing images of active faults are the remote sensing images which can reflect the dislocation of late Quaternary strata, geological bodies and geomorphic surfaces(unit).

The latest active age, slipping senses and active intensity of above active faults in the area, as well as the overall tectonic pattern and seismic capacity of active structures in the area are discussed. The MargaiCaka fault in the north of the study area and the Riganpeicuo fault, the Qixiangcuo fault in the south are large-scale left-lateral strike-slip faults of NEE trending and have the capability of generating earthquakes of about magnitude 7.5. The NEE-trending Yibuchaka graben, the Qingwahu fault, and the NW-trending Dongcha fault in the central of the map unit have the capability of generating earthquakes of about magnitude 7. The above-mentioned faults reflect a special dynamic environment in which the area is squeezed in the north-south direction, and a V-shaped conjugate fault formed, making the plateau squeezed out to the east.

Key words: Tibet area, Holocene fault, Typical remote sensing images, Qiangtang Land, V-shaped conjugate fracture system

摘要：

西藏地区地壳活动强烈, 活动断层发育, 存在很大的地震灾害风险, 因此查清活动断层的分布是一项重要工作。遥感解译是查明活动断层最有效的手段, 其核心技术是正确把握活动断层的典型遥感影像特征。文中结合 1︰100万全国地震构造图(西藏区)编制工作, 利用高分辨率卫星遥感影像对西藏地区改则幅(I45)全新世活动断层的典型遥感影像特征进行了研究, 确定了区内全新世活动断裂玛尔盖茶卡断裂、 日干配错断裂、 依布茶卡地堑、 青蛙湖断裂、 东查断裂、 其香错断裂中段的空间展布。结合前人的研究成果及区域对比分析, 讨论了区内全新世断裂的最新活动时代、 活动性质和活动强度, 以及区内活动断裂的整体构造运动特征和发震能力。研究区北部的玛尔盖茶卡断裂和南部的日干配错断裂、 其香错断裂为较大规模的NEE向左旋走滑断裂, 具备发生约7.5级地震的能力。 中部还发育了NEE向依布茶卡地堑、 青蛙湖断裂和NW向东查断裂这3条规模相对较小的全新世断层, 具备发生约7级地震的能力。上述断裂反映了该区受到SN向挤压, 形成“V”字形共轭系统, 总体运动特征表现为块体向E挤出的动力环境。

关键词: 西藏地区, 全新世断层, 典型遥感影像, 羌塘地块, “V”字形共轭断裂系