1. General characteristics of translational faultsTranslational faults are faults in which the two disks of the fault basically slide relative along the strike of the fault. According to the relative sliding direction of the two disks, it can be further named the right-line translational fault and the left-running translational fault, the so-called right-line or left-side line refers to the right line when standing on any part of the fault to observe the counter-plate, the right-line person who slides to the right of the counter-plate is the left-line line, and the person who slides to the left is the left line. If it is a group of geese-row translational faults, it can also be divided into left-order and right-order according to the arrangement and partial superposition relationship between the geese-row faults. The left-step type refers to the observation along the strike of the fault, and then rises to the left staggered column, as if going up the step; The right-step type refers to the observation along the strike of the fault, and then rises to the right, as if it were going up a step (Fig. 6-32).
The translational fault plane is generally straight, steep and even upright. If a fault cross-cuts into inclined strata (inclined faults), the fault effect from the cross-section is often consistent with that of the normal or reverse fault, and sometimes there is a certain degree of down-dip sliding, so some large translational faults are often mistaken for normal or reverse faults.
Large translational faults are often characterized by strong fracture zones, dense shear zones, breccia lithification zones and super-fractured lithification zones, and the shear fragmentation is more intense than the other two types of faults.
2. Geological background
The geological background of the development of translational faults can be divided into two categories: one is the translational faults associated with wrinkles and other structures, and the other is regional translational faults. The translational faults associated with folds or large thrust faults are generally not large, mainly play the role of structural transformation and displacement regulation, and are often oblique or cross-intersected with folds or thrust faults. The translational faults of the oblique structural line are developed along a pair of conjugate shear planes. The translational faults of the cross-alternating structural line may have developed along the tension fracture plane and were formed under the impetus of differences. The translational faults of these two occurrences, especially the oblique translational faults, are widely developed in the European Jurassic structure.
Large translational faults are formed by regional force-couple tectonics, which are called strike-slip faults. There are some well-known trend-slip faults in the world, such as the San Andres fault on the west coast of the United States, the Alpine fault in New Zealand, the Tanlu fault on the mainland, and the Altun Mountain fault.
3. Stress field analysis of translational faults
(1) The stress state of the translational fault zone controlled by the two main strike-slip faults
Translational faults are formed and developed under single shear stress, and have specific secondary stress fields in different directions and intervals within the translational fault zone, and various secondary folds and fracture structures are formed in each specific part (Fig. 6-33).
(2) The stress state at the end of the translational fault is at the end of the straight shear zone, and the main fault is often bifurcated into a set of horsetail filamentous secondary faults, and a compressive fracture fan is formed at the end of the general sliding direction. A tensile fracture fan is formed at the other end of the sliding pointing (Figure 6-34). This divides the entire shear zone into four stress state quadrants (Fig. 6-35).
4. Some phenomena related to strike-slip faults
The study of some famous large translational faults (strike-slip faults) in the world has found some remarkable phenomena, such as differential uplift and fault block uplift associated with faults; One is the folds associated with faults.
In the San Andrés Fault Zone and its flanks, there are a number of fault basins. It is concluded that in translational fault activities, due to the local deflection of the fault trend, the extension and collapse of the rock block at one end of the fault block (Fig. 6-36B) will be caused, and basins and depressions will be formed. At the other end, it causes extrusion and overlap, forming folds or thrust faults (at Figure 6-36A). When two translational faults with different strikes and opposite directions are intersected and cut into wedge-shaped rock blocks on the plane, the wedge-shaped rock blocks will slide up and down with the horizontal movement of the faults on both sides. As shown in Figure 6-37, if the wedge-shaped rock block moves towards the wedge tip, the wedge-shaped rock block rises and the surrounding rock blocks fall. Conversely, when the wedge moves away from the tip, it causes the wedge to fall and the surrounding rock to rise.