Abstract:

 In this paper we use the new brittle faulting theory, the “noncoordination criteria”, to expound and analyze the mechanical mechanism of basement preexisting fabric controlling fault formation and evolution, to determine the law of change in preexisting basement fabric activity, and to investigate the controlling role of basement preexisting fabric on fault formation and evolution. Through the study we came to the following conclusions. (1)The basement preexisting fabric (particularly the preexisting fault) has priority in activity, which is the root cause of its control over fault formation and evolution in sedimentary basin. (2)The controlling power of preexisting fabric on basin faulting is determined by its activity that is controlled by the attitude and mechanical property of the preexisting fabric, as well as its stress state, and its activity can be quantitatively described using the activity coefficient (fAS) of preexisting fabric.(3)The faults controlled by basement preexisting fault exhibit remarkable regularity in their locations and trends (strikes), formation orders, inherited features, and the size distributions. (4)The controlling power of basement preexisting fault is the strongest when the fault is perpendicular to the extension direction of the controlled fault and the angle between the preexisting fault and the σ1 of the controlled fault is 45°-(/2); when the angle (α) between the strike of the preexisting fault and the extension direction of the controlled fault becomes smaller gradually, and the dipangle deviated from 45°+(/2), the controlling power will be reduced progressively. (5)The larger the size of the preexisting fault is, the more intensive the controlling power of the preexisting fault on fault formation and evolution will be. The faults controlled by largescale preexisting basement faults tend to constitute the structural framework in rift basin. (6)When the shear strength becoming smaller, the possibility of the occurrence of the rupture in the preexisting weakzone will be increasing, and its controlling power will steadily be enhanced, but its affection is relatively weak comparing to the basement preexisting fault. Using the abovementioned conclusions, a theoretical model for the structural interpretation of seismic data may be constructed. These conclusions may also be used as a theoretical guidance for indepth study of fault system formation and evolution in rift basin.

Key words:

Key words: rift basin; fault; preexisting fabric; preexisting fault; activity coefficient; noncoordination criteria