一般情况1989年6月末,在近年来几乎每年都有震群发生的日本伊豆半岛以东近海,继5月下旬持续约3周的震群之后,又出现了频繁的震群活动。从6月30日到7月11日凌晨,地震总数超过21000次,其中有感地震464次,最大震级5.5(7月9日,两次),其次还有一次5.3(7月7日),一次4.9(7月5日),一次4.7(7月7日),震源深度5—10公里,最高烈度(静冈县伊东市)为日本气象厅烈度标度的5度,属近10年来最大的震群。在近一个月 General Situation At the end of June 1989, earthquake swarms near the sea east of Japan’s Izu Peninsula occurred in almost every year in recent years and frequent swarm of earthquake swarms occurred following the swarm that lasted for about three weeks in late May. From June 30 to the early hours of July 11, the total number of earthquakes exceeded 21,000, of which 464 were felt, the maximum magnitude was 5.5 (July 9, twice), and the second was 5.3 (July 7). A time of 4.9 (July 5), a 4.7 (July 7), the focal depth of 5-10 km, the highest intensity (Ishi-shi, Shizuoka) Japan’s Meteorological Agency intensity scale of 5 degrees, which is the past 10 years The largest earthquake swarm. In nearly a month