迭加断裂形成机制及其与构造应力场演化关系

地质体是在地壳演化中形成的,它是建造和构造形变的综合体。断裂化的地质体在较晚期构造力或工程载荷作用下沿已存在的断裂发生形变和位移的现象被称为迭加断裂,其形成过程即是迭加断裂作用。 本文以莫尔-库仑理论为基楚,探讨断裂发育与迭加断裂作用、构造应力场的关系,并对地质构造研究中的“断裂继承”,“断裂复活”进行定量的探讨。研究过程中承谷德振老师指导和鼓励,于此表示衷心的感谢。

MECHANISM OF THE FORMATION OF SUPERIMPOSED FAULT AND ITS RELATION WITH EVOLUTION OF TECTONIC STRESS FIELD

The deformation and displacement along preexisting faults,resulting from the action of engineering load or post-tectonic force on the faulted geologic body and cracked rock mass,are called superimposed faults.An empirical formula for the relation between the shear strength of tectonite in the fault zone and that of mother rocks is suggested; tgφ=1/2tgφ₀.(where φ and φ₀ are the angle of internal friction for tectonite and mother rock respectively);S=(1/3-1/6)/S₀ (where S and S₀ are.the original shear strength of tectonite and mother rock respectively).According to our calculations and analysis under a new stress condition of α=10°-70° (where a is the angle between the preexisting fault and maximum principal stress,shear superimposed fault may be formed in the mother rock with internal friction angle φ= 20°.Both α₁ and α₂ are called the critical shear angle,where α₁ and α₂ are the minimum and maximum value of angle a respectively Therefore,shear superimposed fault can be formed by the preexisting fault under the condition of α₁>α<α₂.IN 10° formed;as generally is fault superimposed α<10°tensile field,as formed.In be would etc.) fault,thrust (reverse compressive α="0,tensile" as formed; the 2.As Table in given 60°are and φ₀="30°,40°,50°" rock mother of angles friction internal for mass faulted α₂α₁ angle shear critical suggested paper,the this>α<70°,shear superimposed fault is generally formed (Fig 6).There is an optimum shear angle or a most dangerous slipping angle a,among the critical shear angles.Angle a,represents the angle between σ₁ and the fault plane,along which shear superimposed fault is most easily formed.The angle α_r= 40°to 20° for mother rocks with φ₀=20° to 60° are listed in Table 3.Under the action of polycyclic tectonic force in various directions,there exist no more than four sets of original shear faults and six sets of limited faults in a single geologic body.Under a condition of a given recent tectonic stress field,the faults with a equal to or approximate to a can be considered to be the most dangerous faults or the seismogenic faults in the region in question.Bades on the above-mentioned conclusions,the earthquake risk and regional stability of Earth’s crust can be predicted and determined.For the regions where exist deep seated basement faults with great elongation formed during polycyclic movements and historically occurred a number of earthquakes,or for the Cenozoic rift-valley regions,as the North China region,and Hengduan mountain ranges and so on,a can be selected as 40°-30°.As for the regions where the basement faults are not on a large scale and the historical earthquakes more seldom occurred,for instance the South China region,the angle a can be selected as 25°-20°.