地震空区及条带附近地震破裂特征的震例研究

STUDY ON THREE EARTHQUAKE CASES FOR FRACTURE FEATURE OF MODERATE AND SMALL SHOCKS NEAR SEISMIC BELTS AND GAPS

选取邢台 1 981年MS5.8、菏泽 1 983年MS5.9和射阳 1 987年MS5.1三个震例 ,研究了孕震中后期中小地震的破裂特征 .结果表明 :震前区域内中小地震多倾向于单侧破裂 ;邢台、菏泽地区的中小震具有优势的破裂面走向 ,与主震破裂面一致或共轭 ;震前中小地震的环境应力值τ0 略大于正常时期 ;射阳不存在优势破裂面走向 ;菏泽MS5.9和射阳MS5.1孕震空区边缘上的地震都倾向于单侧破裂 。

Three cases of Xingtai M S5.8,Heze M S5.9 and Sheyang M S5.1 earthquakes are chosen and the fracture feature of moderate and small shocks before the earthquakes are studied.The result shows:1.The shocks occurred during the seismogenic period show ten dency of unilateral fracture;2.The shocks before Xingtai and Heze earthquakes possess a dominant direction of fracture plane,that is similar or conjugate to the strikes of seismic belts and fracture planes of main earthquakes;3.The environment stress τ 0  of the shocks before the earthquakes is slightly larger than those during the normal period;4.There is not a dominant direction of fracture plane for the shocks before Sheyang earthquake, therefore it is deduced that there is not seismic belt before the event;5.Before Heze and Sheyang earthquakes,the moderate and small shocks occurred on the edge of seismic gaps show tendency of unilateral fracture, and their directions of principal fracture generally do not point to the interior of gaps.