兰州地区活动构造的基本特征

PRINCIPAL FEATURES OF THE ACTIVE TECTONICS IN LANZHOU AREA

兰州地区发育了NWW向和NNW向 2组主导性活动构造带。大致以河口为界 ,东部地区主要为NWW向的马衔山 兴隆山左旋逆走滑活动断裂系 ,其新活动明显 ,是区内的主要控震断裂 ,112 5年兰州 7级地震就发生在其中的马衔山北缘断裂带的西端。河口以西为拉脊山北缘断裂和庄浪河断裂等 1组NNW向的弧形逆冲断褶带 ,变形方式以断裂扩展褶皱为主 ,其新活动可能导致了 138年金城 -陇西 6 34 级地震、144 0年永登 6 14级地震和 1995年永登 5 8级地震的发生。兰州市区所在的兰州盆地则夹持在上述 2组活动构造之间 ,其内同样发育了NWW向和NNW向的次级断裂 ,如刘家堡断裂、金城关断裂、雷坛河断裂及深沟桥断裂等 。

Lanzhou area developed two groups of dominant active tectonics:one group is NWW direction,another one is NNW direction.By the boundary of Hekou,the structure pattern of eastern area is NWW direction Maxianshan-Xinglongshan reverse left lateral strike-slip fault system. Their new activities are very strong,so they formed the main controlled earthquake faults,Lanzhou earthquake with magnitude 7 in 1125 had just happened in the west segment of this fault zone. In the western area of Hekou, there are group of arc thrust-fold zones by NNW direction,such as the northern margin fault of Lajishan Mountain and Zhuanglanghe fault,etc. The characteristic of deformation is fault propagation folding,their new activities had caused a series of earthquakes happening,such as Jincheng-Longxi Ms 634 earthquake in 138,Yongdeng Ms 614 earthquake and Kushui Ms 512 earthquake in 1440,Yongdeng Ms5.8 earthquake in 1995,etc.Lanzhou basin is blended in the two groups of active tectonics,there are also developed two groups of NWW and NNW direction secondary faults which relative each other,such as the Liujabu fault,Jinchengguan fault,Leitanhe fault and Shengouqiao fault,etc.These faults have the structural condition to breed and happen middle and strong earthquakes.