1On August 25th, 933, a magnitude 7.5 earthquake occurred in Diexi Town, 60km north of Maoxian County, Sichuan Province, with the epicenter intensity of 10 degree and the focal depth of 6. 1 km. According to historical records, when the earthquake occurred, the ground was covered with yellow fog and there were few battlements left. The central part of the city almost plummeted within a few minutes of the violent earthquake, and the descending distance of a single stepped earthquake reached 500-600 meters, so Diexi Town no longer existed. Before the earthquake, there were many abnormal phenomena in this area: dogs cry and sheep hiss, snakes scare mice, crows cry and hens. It is said that a shepherd boy actually flew over two mountains.
The huge landslide cut off the Minjiang River, dammed the lake and spread to Dujiangyan. More than a month after the earthquake, it rained continuously in the upper reaches of Minjiang River, the river surged and the number of lakes in Haizi Lake increased day by day. On the 45th day after the earthquake, Haizi Waterfall in Diexi River collapsed and accumulated water poured out. The rapids rushed to Maoxian and Wenchuan at a speed of 30 kilometers per hour, which triggered a rare secondary flood in the history of China earthquake.
On August 1976, 16, an earthquake of magnitude 7.2 occurred between Songpan and Pingwu in Sichuan Province. The earthquake was a swarm type, followed by a magnitude 6.7 earthquake on the 22nd and a magnitude 7.2 earthquake on the 23rd. The range of earthquake sensation is wide, reaching Gao Tai in Gansu province in the west, Kunming in the south, Hohhot in the north and Changsha in the east, with the maximum radius of 168. Landslides, falling rocks, mudslides, etc. It has caused serious damage to farmland, roads, river beds, etc. , communication is interrupted. The earthquake occurred in a sparsely populated mountainous area, and measures were taken to evacuate people before the earthquake. So there were only more than 800 casualties, including more than 600 minor injuries.
The first two earthquakes were 43 years apart, and the last earthquake was 32 years away from this Wenchuan earthquake. It can be seen that Wenchuan itself is an earthquake-prone area and should be the most important monitoring area for seismologists!