山东地区地壳三维纵横波速度和泊松比结构及其对地震活动性的影响

3-D P and S wave velocity of crust and Poisso’ns ratio structures and their influence on seismic activity in Shandong area

基于山东及邻区丰富的P波和S波到时数据反演获得了研究区内高精度的三维纵横波速度结构和泊松比异常分布形态。结果表明:2020年济南长清M_(S)4.1地震震中位于P波、S波高低速异常和高低泊松比异常过渡带,可能是区域构造应力下长清断裂发生左旋走滑运动的结果;2003年青岛崂山M_(L)4.1地震、崂山震群、乳山震群和长岛震群等的发生可能都受到流体的强烈影响,流体沿已有的较大断裂或相对完整岩体内的裂隙侵入,诱发断裂活动或裂隙破裂,从而导致中强地震或震群活动的发生。

Shandong area is located in eastern China,where faults develop and earthquakes occur frequently,so high resolution velocity structure is quite necessary for better understanding causal mechanism of earthquakes.Based on abundant P and S wave arrival times recorded at stations in and around Shandong area,high resolution 3-D P wave velocity,S wave velocity and Poisson’s ratio structures are obtained.The results reveal that,the hypocenter of the 2020 Changqing M_(S)4.1 earthquake is located in the transition zone where seismic velocity and Poisson’s ratio change drastically in the horizontal direction.This suggests that the 2020 Changqing M_(S)4.1 earthquake may be caused by the sinistral strike-slip movement of the Changqing fault affected by the regional stress field.Occurrence of the 2003 Laoshan M_(L)4.1 earthquake and Laoshan,Rushan and Changdao earthquake swarms may be strongly affected by fluids.These fluids invaded along pre-existing faults or cracks in relatively intact rock bodies,and induced faults to act or cracks to break up,which caused the occurrence of middle and strong earthquakes and earthquake swarms.