一、概况1985年3月29日19点15分,在四川省自贡市境内,发生了4.8级地震。根据四川地震台网测定,仪器震中位于北纬29°22′08″,东经104°49′34″;宏观震中在自贡市大安区的凉高山——燕子山一带。主震发生后的10小时之内,断续发生较强有感地震三次,其后数日,发生余震100多次,但强度、频率 I. Overview At 19:15 on March 29, 1985, a magnitude 4.8 earthquake struck within Zigong City, Sichuan Province. According to the Sichuan Seismic Network, the instrumental epicenter was located at latitude 29°22′08′′ north latitude and longitude 104°49′34′′ east longitude; the macro-epicenter was in Yanliangshan, a cool mountain in the Da’an District of Zigong City. Within ten hours after the main shock, strong and sensitive earthquakes occurred intermittently three times. In the following days, there were more than 100 aftershocks, but the intensity and frequency