Abstract: This paper demonstrates the results of shallow seismic exploration of the Liuwu-Dafosi Fault in the vicinity of Lhasa City. On spot map, the segment of the fault in mountainous area can be identified distinctly, but the segment in river valley is unidentified. Shallow seismic exploration reveals that the fault dissects Tertiary or Quaternary strata. Geological interpretation of shallow seismic reflection profile reveals a velocity structure of five layers. Layer 1 to layer 4 have a velocity ranging from 0.8km/s to 2.0km/s or 2.8km/s, and can be assigned to Tertiary or Quaternary strata. Layer 5 has a velocity ranging from 3.0km/s to 4.0km/s, which is supposed to be granite bedrock according to its scattered distribution in CDP stacked section and geological evidence. The Liuwu-Dafosi Fault can be identified at 320m distance of the shallow seismic reflection profile located to the southwest of the Lhasa City. The fault is dipping northeast at an angle of 80?, the highest point of which is at 100m depth. It is determined that the fault is an active reverse fault.

Key words: shallow seismic exploration, active fault, Lhasa City

摘要： 简要介绍了在青藏高原拉萨市附近刘吾-大佛寺间断裂的浅层地震勘探工作,并进行了初步的地质解释.结果表明,刘吾-大佛寺间断裂所在区域的速度模型为5层结构.第1层至第4层的介质深度从0m变化到20m,P波速度800～2 000或2 800m/s,介质为第四纪或第三纪覆盖层;第5层的介质P波速度在3 000～4 000m/s以上,其CDP图像分布零散、没有形成较强的反射界面,推测该区域为花岗岩类的基岩区.根据反射波组的连贯性、间断性及位置,判定在浅层地震勘探剖面320m处存在着刘吾-大佛寺间断裂,它是1条逆断层,倾向NE,倾角80°左右,其上端点出现在深约100m处.

关键词: 浅层地震勘探, 活断层, 拉萨地区