辽东半岛中强地震活动及其与构造相关性

摘要

Moderate-strong earthquakes happened very frequently in the Liaodong peninsula.In addition to the Haicheng M7.3 earthquake in 1975,there are also 19 earthquakes of M≥5 recorded in this area.The earthquakes are distributed regularly,mainly restricted to seismic belts or to the grid nodes.The spatial distribution is accordant to the NE-NNE trending faults such as the Jinzhou Fault,the Yalujiang Fault,and to the NW-trending conjugated ones.Moderate-strong earthquakes happened mostly near the tectonic basins where two sets of faults intersect,or close to the NW-trending tectonic belt.The NE-NNE and NW-trending faults are a pair of conjugate sheer fracture planes characterized mainly by lateral strike-slip movement under the action of the contemporary NEE-directed nearhorizontal principal stress.The NE-NNE faults belong to the inheritance fault,which control the regional geological tectonic pattern and its evolution,often large in size ; while the NW ones mostly belong to newly-generated fault,and their size is usually related to the size of NE-NNE faults they conjugate with.The study shows that the moderate-strong earthquakes in the Liaodong peninsula are controlled mainly by the NE-NNE structures,and the seismogenic structures are basically the NW faults.Meanwhile,correlated with the size of the NW faults,the moderate-strong earthquake activities show a trend of decreasing gradually from north to south and from west to east,and the magnitude of them decreases roughly from M7 ～7.5 to M5.5 ～ 6 or so.%辽东半岛是中强地震活动较多的地区,除1975年海城7.3级地震外,这一地区还记录了≥5级地震19次.区内中强地震分布具有较好的规律性,基本上局限于地震活动条带及其网格的结点部位,空间分布上与金州断裂、鸭绿江断裂等NE-NNE向断裂及其共轭的NW向构造一致,且多发于2组构造交会部位的构造盆地或偏于NW向的构造带附近.NE-NNE向和NW向断裂是在现今NEE向近水平主压应力作用下所形成的一对平移走滑性质为主的共轭剪切破裂面,NE-NNE向断裂属于继承性破裂,规模大,对区域地质构造格局及其演化具有控制作用；NW向断裂多属于新生破裂,其规模通常同与其交会的NE-NNE向断裂有一定的相关性.研究表明,辽东半岛中强地震活动受到了NE-NNE向断裂的控制,但其发震构造基本上是NW向断裂,同时,与NW向断裂的规模相关联,中强地震活动存在由N向S、由W向E逐渐减弱的变化规律,地震强度大致从7 ～7.5级降为5.5 ～6级.