According to historical records in the early Western Han Dynasty, the birthplace of Han Shui was located in the southwest of Tianshui City, Gansu Province, when the upstream of Han Shui was now Liuyang County, Shaanxi Province, there were a number of mountain lakes, these lakes were called Tianchi Daze, because these lakes stored enough water, the upstream of Han Shui was unimpeded, at that time it was possible to take a boat from Hanzhong City, Shaanxi Province, and go up the Han River to reach Longxi, and down the river to reach Eastern Chu.
On February 22, 186 BC [ the twenty-seventh day of the first month of the second year after Han Gao ] earthquake, the Landslide of Qiangdao in Wudu Province, the earthquake ended in August, crushing more than 860 people.
According to historical records, it can be found that on February 22, 186 BC, a particularly large earthquake occurred in the area of Wudu in Gansu Province - Luoyang County in Shaanxi Province and Ningqiang County in Shaanxi Province - Qingchuan County in Sichuan Province, which caused landslides in wudu, Zhouqu, and Liuyang County in southeastern Gansu Province, and strong aftershocks lasted for 8 months, and the earthquake killed at least 860 people.
Modern geological surveys and expeditions have found that there have been extra-large landslides in the hanwang mountain area in the territory of ningqiang county in modern Shaanxi Province, and it is precisely because of this landslide that the guhan river upstream [modern Han water] is blocked to form a dammed lake, and in 161 BC, the water of the dammed lake overflowed from the south of the dammed lake into the ancient diving channel and then flowed into the upper reaches of the Jialing River to complete the Jialing River to seize the ancient Han water [modern Han Shui] channel.
Historical records record that the main areas damaged by the earthquake in 186 BC were Wudu Dao and Qiang Dao, which were mainly manifested as landslides; Wudu Dao was located near the modern Luoyang County in Shaanxi Province, while Qiang Dao was located near Zhouqu County in modern Gansu Province. Official ranging shows that the straight-line distance between Zhouqu County in Gansu Province and Luoyang County in Shaanxi Province is about 173 kilometers. Historical records record that landslides occurred in Wudu Province and QiangDao; the corresponding seismic intensity of landslides was 10 degrees or more (because only earthquake intensity of 10 degrees or more would lead to landslides].
In addition, the straight-line distance between the ancient Wudu Road [modern Luoyang County, Shaanxi Province] is about 32 kilometers away from the area where the landslide blocked the river channel in the ancient Han River, and the seismic intensity of the area where the landslide blocked the river channel in the ancient Han River should also be 10 degrees or more.
Therefore, it is speculated that the area of the great earthquake that occurred on February 22, 186 BC at the junction of Sichuan, Gansu and Shaanxi with an earthquake intensity of 10 degrees was a northwest-southeast direction, with an area of more than 173 kilometers long and more than 32 kilometers wide.
Official information shows that on May 12, 2008, a magnitude 8 earthquake occurred in Wenchuan, Sichuan, China, with a focal intensity of 10 degrees or more, an area of 224 kilometers long and 28 kilometers wide.
By comparing the area with the earthquake intensity of 10 degrees or more in the Sichuan-Gansu-Shaanxi junction earthquake in 186 BC and the area with the magnitude 8 earthquake earthquake in Wenchuan, Sichuan in 2008 with an earthquake intensity of 10 degrees or more, it can be found that the distribution range of the great earthquake intensity of the Sichuan-Gansu-Shaanxi junction in 186 BC and the intensity distribution range of the 8-magnitude earthquake that occurred in Wenchuan, Sichuan in 2008 are very similar, so it is speculated that the magnitude of the two earthquakes should not be much different.
Therefore, according to the distribution range of earthquake intensity, we believe that the magnitude of the earthquake that occurred on February 22, 186 BC at the junction of Sichuan and Gansu and Shaanxi should be between magnitude 7.5 and 8. [Previously, a paper on the 186 BC Wudu earthquake in Gansu province by the Gansu Earthquake Research Institute of the China Earthquake Administration believed that the magnitude of the earthquake was between 7 and 7.25; and the catalogue of strong earthquakes in Chinese history published by the National Earthquake Defense Department in 1995 stated that the magnitude of the 186 BC Wudu earthquake in Gansu should be between 6 and 7. 】
conclusion:
1. On February 22, 186 BC, a major earthquake occurred at the junction of Sichuan, Gansu and Shaanxi [between Qingchuan County in Sichuan Province and Ningqiang County in Shaanxi Province and Luoyang County in Shaanxi Province and Longnan in Gansu Province] directly caused the upstream of the Ancient Han River to divert the current Western Han Water into the Jialing River to complete the Jialing River to seize the Ancient Han River.
2. The whole process of the Jialing River seizing the ancient Han River is speculated to be as follows: on February 22, 186 BC, a large earthquake occurred at the junction of Sichuan, Gansu and Shaanxi, and the magnitude of the earthquake should be estimated to be 7.5 to 8 magnitude; the earthquake caused a large-scale landslide and landslide in the south of Hanwang Mountain in Ningqiang County, Shaanxi Province [east of Daijiaba Town, Ningqiang County, Shaanxi Province], and the landslide blocked the river channel in the upper reaches of the Ancient Han River to form a dammed lake.
In 185 BC, about 1 year after the earthquake, there was a dam collapse in the dammed lake, and a large number of floods rushed down the ancient Han River channel to attack the Han Middle Han River coast, and in 180 BC, about 6 years after the earthquake, there was a dam collapse in the weir lake, and a large number of floods rushed down the ancient Han River channel to attack the Han Middle Han River coast again. However, due to the relatively strong dam body generated by the 186 BC earthquake, the dammed body did not completely collapse and continued to store water to form a dammed lake.
In 161 BC, the dam collapsed in the south of the dammed lake affected by exceptionally heavy rainstorms, and the lake water flowed into the Jialing River along the ancient diving river channel, and finally completed the process of the Jialing River seizing the upper reaches of the ancient Han River.
3. According to the duration of the aftershocks of the Sichuan-Gansu-Shaanxi junction earthquake on February 22, 186 BC and the regional distribution range of the earthquake intensity of 10 degrees or more after the earthquake, it can be speculated that the magnitude of the large earthquake that occurred on February 22, 186 BC at the junction of Qingchuan County, Sichuan Province, Longnan County, Gansu Province, Liuyang County and Ningqiang County, Shaanxi Province should be 7.5 to 8 magnitude. [Previous official research has concluded that the magnitude of this earthquake is 6 to 7 or 7 to 7.25 is a significant underestimation of the magnitude]