Analysis On The Faults And The Possibility Of Earthquakes Induced By Them In Daqing City

Daqing region is situated in the middle-north of Songlao basin, the tectonics inducing earthquakes in this region are mainly influenced by the pressing force of the Pacific plate to the northeast Asian continent, there were 6 earthquakes, which MS were not less than 6.8 among the earthquake records in the history, and the most dangerous earthquake occurred in 1119. Daqing city, on the whole, belongs to the weaker part in the northeast earthquake regions, but the earthquakes on a little scale occurred more frequently since 1970. Because the Yilan-Yitong fault belt has blocked and weaken the effect from the Pacific plate diving, it was difficult for the energy to accumulate to induce earthquakes on a large scale in the basin.The geophysics fields and the deep structures in the Daqing region show that the region is steadier and is not the place where earthquakes occur frequently.According to the developing depth and grade of the faults, the lithosphere faults, the crust faults, the basement faults and the cover faults were divided. Twelve deep and great faults are developed in Daqing city and its adjacent areas, they include Nenjiang fault, Keshan-Da'an fault, Fuyu-Zhaodong fault and the second Songhuajiang fault etc, and they have been active in different degree since early Pleistocene.The cover faults in Daqing region are mainly developed in formation of Huoshiling member late Jurassic and its cover formations. According to their formation period, activity characteristics and penetrating relationship, four types of faults were divided, that is fault-depression faults, depression faults, inverted-strike-slip faults and inverted-extension faults; According to the activity history of the faults, five types of faults were divided, that is long-term active faults, early active faults, early-medium-term active faults, medium-term active faults and terminal active faults.It is possible for the terminal activity faults to penetrate to the Quaternary, but their scale is generally small and the penetrating distance is short, therefore, they can not induce earthquakes on a large scale. The remote sense images of last thirty years in Daqing region show that the linear tectonics have not changed remarkbly, in the meantime, the earthquake timing figure shows that the probability of the faults inducing earthquakes, which MS is no less than 5, is little, though some terminal active faults have penetrated to the Quaternary.Seventeen potential earthquake source areas were divided in the region according to the dividing principles and the signs of earthquake source areas. The research results indicate that the earthquake degree is 6, considering the exceeding probability to be 10 percent in the future 50 years.