Quantitative Seismic Risk Evalution On Blind Active Faults

Fuyu-Zhaodong Fault is an important blind seismogenic fault in Songliao Basin. In 1119 A.D. a 63/4 earthquake happened on the fault, which was the largest earthquake ever before the Haicheng earthquake in 1975 of Northeast China. In 2006 and 2014 occurred several earthquakes below Ms6.0 on the fault; the modern earthquakes mainly centralized on the northeast segment and the Chaganhua segment. After our active fault detection on the Songyuan City during 2012 to 2014, the northeast segment of Fuyu-Zhaodong fault was proved to have crossed the downtown of Songyuan City, being nearly east-west trending and obviously partitioned and independent.. During the active faults detection work in Songyuan we found a active fault, which was called Gudian fault; In this article, detailed underground structure of the fault is obtained through 3D seismic data, the latest activities and sliding rate are obtained from the shallow seismic exploration and the terrace borehole work; On the basis of comprehensive study on the geological structure, the quaternary activity, historical earthquakes and earthquake activities of the fault, etc, we evaluate the potential maximum earthquake magnitude on subsurface fracture parameters, to confirm the fault to be active since late Pleistocene, with the ability of magnitude 7 earthquakes. In addition, recurrence period or annual rate is calculates by seismic moment ways. The historical earthquake recurrence probability model of Chinese mainland is adopted to calculate the occurrence probability of the Gudian Fault in the coming 50~200 years. The urgency and importance of meticulous detection of the faults is obvious. Through three dimensional geophysical data from oilfield and shallow geophysical prospecting, the space distribution and profile characteristics of faults was determined; united drilling detection and optical stimulated luminescence dating were also used to confirm seismic activities of the faults as being active since late pleistocene. This paper, using the scale of bedrock surface rupture from three dimensional geophysical data, estimates the seismic potential of the North-Fuyu and Gudian Fault and studies their probabilistic seismic risk in probabilistic calculation method. Poisson probability model is adopted and quantitative parameters such as the maximum magnitude, recurrence period and occurrence probability in the coming 50~200 years are calculated. Especially in the oil field area on which three dimensional seismic data is rich, it is easier to obtain large area active faults fracture scale on bedrock accurately, to get closer to the actual situation of empirical formula of magnitude- fracture parameters. It is a breakthrough of study on potential seismogenic fault with little historical earthquake records and with long recurrences; the research also has certain significance on the impact of the earthquake surface rupture scale with different coating conditions.