1982年卢龙地震前后的小震震源参数

SOURCE PARAMETERS OF SMALL EARTHQUAKES BEFORE AND AFTER THE 1982 LULONG EARTHQUAKE

1982年10月19日,在唐山余震区的东北端卢龙,发生了一次M_L=6.2(按北京电信传输台网的目录)的地震(39°57′N,119°04′E).为了监视卢龙地震前后小震震源参数的变化,本文考察了唐山-卢龙地区自1980年1月至1984年6月的情况.利用P波初动半周期,测定了160次M_L=2.7—4.3的地震的震源参数.在所研究的震级范围内,初动半周期和震源半径不随M_L而增大,应力降则随M_L而增大。应力降的数值在0.1—50MPa的范围内变化,且主要集中在1MPa和5MPa之间.因此本文认为,对此地区,5MPa以上为高应力降,1MPa.以下为低应力降.该地区地震的空间分布表明,高应力降事件与随后发生的M_L≥5的地震有明显的关系.在卢龙地震前一年多里,整个地区内的高应力降事件减少,低应力降事件增多;但在卢龙地震的震中附近发生了两次高应力降事件.

On 19 October 1982,an earthquake (39°57'N,119°04'E) with ML = 6.2 (according to Catalog of the Beijing Telemetered Seismic Network) occurred in Lulong on the northeastern edge of the aftershock zone of the Tangshan 7.8 earthquake of 1976. Earthquakes in the Tangshan-Lulong region from January 1980 to June 1984 have been examined for monitoring the variations in source parameters of small earthquakes before and after the Lulong earthquake. Source parameters of 160 earthquakes,2.7≤ML≤4.3,were determined using the P-wave first motions. In the magnitude range studied the P-wave first impulse width and the source radius do not increase with ML,and the stress drop increases with ML. The values of stress drop vary in the range from 0.1 MPa to 50 MPa,and are concentrated primarily between 1 MPa and 5 MPa; so in this paper stress drops of 5 MPa and more are taken as high stress drops and that of 1 MPa and less as low stress drops for this region. The spatial distribution of earthquakes in this region shows an apparent relation between high stress drop events and succedent ML≥5 earthquakes. Within one year and more before the Lulong earthquake,in the vicinity of its epicenter occurred two high-stress drop events,but in the whole reigon the number of high-stress-drop events decreased and that of low-stress-drop events increased.