昌马断裂东段断层年龄的确定和大震复发周期的估计

本文以野外地质调查资料为依据,利用地质的方法,讨论了昌马断裂东段的断层崖特征、断层位移量和沿昌马断裂带的古地震证据,确定了断层崖年龄和断层活动速率,粗略地估算了大震复发周期。研究结果表明自全新世以来北东东向断裂的活动性质由压性变为左旋张扭性;断层崖是断裂左旋张扭性活动的结果。断层的水平位移具有分级特点,断层崖具有两个明显的坡度中断,其形成年龄分别为12760年和1880年。公元104年前后,沿昌马断裂可能发生过一次7～7(1/2)级地震,大震复发周期为2620年(考虑蠕滑)和1500年(不考虑蠕滑),12760年和1880年以来的断层水平运动速率分别为4.5毫米/年和6.5毫米/年,水平位移与垂直位移之比值为4.7。

AGE OF FAULT-SCARPS AND EARTHQUAKE RECURRENCE INTERVALS ON CHANGMA FAULT

Based on authers'' field investigations, using geological methods, in the paper we have mainly discussed the fault-scarp features and displacement features in eastern Changma fault zone, some paleoseismic evidences along the fault zone, including the faults formed in Holncene Epoch, ancient slump, drumlin and fault cliff and coarsely ascertained the displacement rates of the NEE fault, the age of the fault-scarps and earthquake recurrence intervals along the faul zone.The studied results show that the active properties of the NEE fault have transformed themselves from extrusion, into left-lateral shear-tension Since Holocene Epoch and the left-lateral shear-tension activity of the fault did form the fault-scarps.An earthquake (Ms=7.5) probably once occurred along Changma fault zone about A.D.104. The recurrence intervals for magnitude 7-7 (1)/(2) earthquake are 2620 years when creep rate is considered, and 1500 years when creep rate is not considered. The strike displacement rate of the fault is 4.5mm/Yr during 12760 years, and 6.5mm/yr during 1880 years. A ratio of strike displacement to the dip is 4.7.