Earthquake trend of Quanzhou earthquake

1604 calculation of the overseas earthquake with M8.04 in Rinan Island and its significance for judging the earthquake trend in Fujian.

Putian No.10 Middle School Zheng

1 1 earthquake with magnitude above 7 occurred in China in the 7th century, including 5 earthquakes with magnitude above 8. The overseas earthquake in Hinan Island occurred on1604,65438+February 29th (thirty-two years of Wanli reign of Ming Dynasty), with magnitude of 8.0, and its epicenter was in Hinan Island, southern Fujian (1 19.5e). Putian and Quanzhou are the most popular places. Numerous rural houses in Putian were dumped, and the pool water dried up due to ground fissures. The land houses in and out of Quanzhou have been dumped, the rocks and sea water have moved, and there are many boats. There are cracks in Tongan, and the water overflows. There are dozens of caves in Zhangpuchang, and mud gushes out. Anxi landslide collapsed. The earthquake affected Zhejiang, Jiangxi, Jiangsu, Guangdong, even Guilin, Guangxi, Tongling, Anhui and other counties and cities. Shanghai and other places are much bigger than the South Australia earthquake with magnitude 7 in Guangdong Province. This is the first major earthquake in Fujian Province, and the only earthquake of magnitude 8 in southeastern China so far. 1445 Zhangzhou earthquake with a magnitude of 6.5, and then 159, until an earthquake with a magnitude of 8 occurred overseas. There have only been five earthquakes of magnitude 5-6 in Fujian Province. Under the background of such seismic activity, it is difficult to give people the impression that an earthquake of magnitude 8 will occur. 1600 The South Australia earthquake with M = 7 and the Rinan Island earthquake with M = 8 overseas are only four years apart. Both earthquakes were on the west coast of the Taiwan Strait, and the epicentres were not far apart. Will the South Australia earthquake with M = 7 promote the Rinan Island earthquake with M = 8?

The Nan 'ao earthquake occurred on September 29th in 1600 (twenty-eight years of Wanli in Ming Dynasty), with a magnitude of 7. The epicenter was located in Nan 'ao Island, Shantou City, eastern Guangdong Province (1 17.2E, 23.5N) with intensity of 9 degrees. The walls, offices and houses in Nan 'ao County collapsed, killing countless people. Earthquake. This is the first earthquake of magnitude 7 in Guangdong Province. 1067 An earthquake of magnitude 6.8 occurred in Shantou-Chaozhou area, which has been 533 years since. If the preparation of an earthquake of magnitude 7 is related to an earthquake of magnitude 6.8, what is the process during this period? Seven earthquakes in our province (1445 M = 6.3 to 1604 M = 8) and two earthquakes in Shantou-Chaozhou area of Guangdong province (1067 M = 6.8 and 1600 M = 7) are arranged in chronological order.

As can be seen from the figure 1, earthquakes are almost distributed in the southeast coast of Fujian and Shantou-Chaozhou area of Guangdong, and move back and forth in the northeast direction. Line A is the main fracture line, and there are two major fractures, Grade 7 and Grade 8. Line B passes through three faults of magnitude 6.8, 6.5 and 4.8, and Line A and Line B tend to be parallel. From the point of view of rock fracture mechanics, a large fracture of magnitude 8 is enough.

As can be seen from Figure 2, the silent period is shortening. On the trend diagram of the average frequency changing with time, the frequency rises sharply when the distance from the main rupture time is less than T/3, and slowly rises around T/ 10, but suddenly rises from T/ 100. It can be considered that the frequency is high and the earthquake has arrived.

Because there are three magnitudes to be calculated in Figure 2: magnitude 7, magnitude 8 and magnitude 7.5, they are discussed separately.

Calculation of Nan 'ao M7 Earthquake in Guangdong Province

The quiet period series is 1-2 2-3 6-7.

July 3781year 22 years

According to the proportional time formula, t is the ratio =(7 1╳22)/378=4 (year).

It is calculated that the occurrence year of the South Australia earthquake with Ms 7 is the year of the last earthquake in 1596 and the Hui 'an earthquake with Ms 4.8 in 10 plus the quiet period, namely:

T is proportional = 1596+4= 1600 (year), which is the same as the actual earthquake occurrence time, that is, this group of quiet periods is proportional.

Calculation of overseas earthquake with M8.0 in Rinan Island

The problem is that an earthquake of magnitude 7 occurred in South Australia, and it takes a long time from magnitude 7 to magnitude 8. The No.7 earthquake is an earthquake with a magnitude of 4.8 in Hui 'an, which is a small earthquake compared with the magnitude of 5.8 in Lianjiang, Fuzhou on the 6th and the magnitude of 7 in Nan 'ao on the 8th. Therefore, the time between the No.6 earthquake and the No.8 earthquake can be regarded as a quiet period (relative), so the quiet period sequence is as follows:

1-2 2-3 6-8

July 3781year 26 years

According to the calculation, the year of the overseas earthquake with M = 8 in Rinan Island is the last M = 7 earthquake in South Australia, which is in direct proportion to the fourth quiet period T = 1600+5= 1605 (year), which is later than the actual earthquake time 1 year.

Interference coefficient α=(4-5)/5=-20%

Calculation of the Qiongshan and Wenchang M 7.5 Earthquakes in Guangdong Province

The earthquake of magnitude 7.5 occurred in 1605, which is the year after the earthquake of magnitude 8 occurred outside Nandan Island, and can be regarded as an aftershock. The M-T diagram follows the earthquake with M = 8, and the previous pattern has not changed at all. Therefore, the static series is still taken as follows.

July 3781year 26 years

According to the proportional time formula, t is the ratio =(7 1╳26)/378=5 (year

The calculated earthquake occurrence year of the Qiongshan and Wenchang Ms 7.5 earthquakes is the year of the last South Australia Ms 7 earthquake plus the fourth quiet period: t proportional = 1600+5= 1605 (year), which is the same as the actual earthquake occurrence time.

Interference coefficient α=0

In other words, the above-mentioned series is directly proportional to the Qiongshan and Wenchang earthquakes with Ms 7.5.

Although the primary earthquakes in Fujian Province are few and small, they also meet the requirements of magnitude 6-7-8 with the earthquakes of magnitude 6.8 and 7.0 in Guangdong. As time goes on, it also appears: calm-strong-prone to earthquakes. From the point of view of rock fracture, the conditions are also mature. In a word, the occurrence of the overseas M 8 earthquake in Rinan Island was the result of the tectonic activities in Fujian and Guangdong. Small earthquake is a summary of Xingtai earthquake experience, and large earthquake has been tested by Haicheng earthquake. But many big earthquakes are not like this. Tangshan earthquake is an obvious example. This is because the structures of various seismic sources are different. Great earthquakes are not universal laws. If we look at a series of long-term earthquakes in an earthquake area, we will find that in the historical series of earthquakes, the quiet period between earthquakes tends to be shortened, which follows the quasi-proportional formula, so it can be summarized as follows: high-frequency and large earthquakes are a universal qualitative law. Of course, there is a high-frequency trend first, and then there is an impending small earthquake.

Secondly, according to the historical data of the earthquake, this earthquake has obvious foreshock, main shock and aftershock, which is the main shock sequence.

1, characteristics of foreshock activity: most small earthquakes occurred in the main earthquake area and its adjacent areas more than three years before the overseas earthquake of magnitude 8 in Rinan Island. The closer to the main earthquake, the higher the frequency and intensity of small earthquakes, and there is a tendency to move to the main earthquake area. Before the earthquake, the earthquake energy release gradually increased.

2. Characteristics of aftershock activity: aftershocks near the main earthquake area are frequent and last for a long time, especially strong aftershocks, which last for about five years and all occur near the Changle-Zhaoan active fault. With the passage of time, the frequency and intensity of aftershocks decrease, and there is a tendency to migrate outside the main earthquake zone, which is called the adjustment of stress field after the main earthquake.

Thirdly, from the analysis of M-T diagram, it can be seen that earthquakes of magnitude 7 or above may not occur in this area in the next few decades. However, studying the trend of seismic activity is a complex subject, and other methods must be used for comprehensive analysis.