【摘要】 山东省成武4.8级地震前二年,在其一侧小地震形成椭圆形围空区,空区长半轴达120公里。同样主震前二年,在以震中为园心,200公里为半径的园面积内小地震分布基本均匀(地震空白区除外);而在主震爆发前半年,小震集中在未来主震位置附近及其外围局部地区,这可能是震前应力急剧集中、调整的短期震兆。相应地在围绕主震震中较大区域内出现约十个月的“缺震”异常,当异常趋近恢复时发震。更多还原

【Abstract】 Two years before Chengwu earthquake(M=4.8), Shandong province, to one side of the earthquake area there was an elliptical seismic gap, the long semi-axis of which amouted to 120 km. During the same period of the two years before the major event in an area with the epicenter as its center and 200 km as its radius, the Small earhquakes were evenly distributed(except in the gap-area). Yet during the half year before the occurrence of the major event, the small shocks were clustered around the location of the future major event and part of its adjacent areas. This might be the shortterm precursor of the earthquake which showed the drastic concentration and readjustment of the stress before the major event. Accordingly, there appeared an“earthquake-absent”anormaly which lasted 10 long months in the large area around the epicenter of the major shock. At the time when the anomalies were about restored to normal, the earthquake took Place.更多还原