【摘要】 龙首山断裂带位于青藏高原向北东推挤的最前缘,是河西走廊与阿拉善地块之间的分界断裂之一.虽然观测精度有限,1954年发生在该断裂带上的71/4级地震是该断裂上少有的有现代地震观测和记录的大地震.本次地震仅在龙首山北缘断裂带两个次级断裂段之间的一条转换断层上形成了长7km左右的连续地震地表破裂带,以北西向右旋兼正断为主要特征,这与区域上近东西向左旋逆断构造运动特征差异较大.经过多次野外调查和地质填图,发现在主断层上没有形成地震地表破裂带,而地震震害的分布又完全受龙首山南北两条断裂所围限,说明地震的孕震可能与龙首山断裂带主断裂有关,转换断层上的地表破裂仅为局部的应力释放.利用震源机制解资料,通过静态库仑应力变化模拟可以看到,如果主震发生在南缘断裂上,对地表破裂有显著的触发作用.综合考虑北缘断层可能存在的动态触发作用,说明目前所见地表破裂是龙首山断裂带主断裂地震的同震响应.小震精定位也显示,龙首山南北两侧的断裂在约10km范围内形成一狭窄的倒三角形,并有向北扩展的趋势.更多还原

【Abstract】 Located in the front margin of the northeastern Tibetan Plateau,the Longshoushan fault zone is one of the boundary faults between the Hexi corridor and the Alxa block.Although the resolution of observation is limited,the 1954 M71/4 earthquake on the Longshoushan fault zone is a rare big event in this zone with modern seismological observation and documentation.During this earthquake,one continuous dextral-normal rupture occurred with a length of only 7 km along a transfer fault connecting two secondary faults of the Longshoushan fault zone.However,the dextral-normal sense of this surface rupture is contrary to the tectonic kinematics in this area.Based on recent field investigation and mapping,two phenomena were discovered.Firstly,except the one appeared on the transform fault,no surface rupture zone is found on the branches of the Longshoushn fault zone.Secondly,the main damage caused by earthquake is distributed on the region between the northern and the southern branches of the Longshoushan fault zone.These two findings indicate that the 1954 earthquake was caused by the main faults rather than the transfer fault of the Longshoushan fault zone,and the co-seismic surface rupture on the transfer fault is only a form of stress release at local portion.According to calculation of static co-seismic Coulomb stress change,the surface rupture could be triggered by an earthquake on the southern branch of the Longshoushan fault zone.Furthermore,in consideration of the possibility of dynamic triggering along the northern branch of the Longshoushan fault zone,the surface rupture should be the co-seismic response to the earthquake occurred on the main branches of the Longshoushan fault zone.Relocation of the small earthquakes also shows that a narrow inverted north-extending triangle about 10 km wide was formed between the northern and the southern faults of the Longshoushan fault zone.更多还原