As a fault, the process from development to activity, maturity and final decline:
The fracture of a complete block begins with shear. In the section with the weakest shear strength or the strongest shear stress, a new micro-fracture system is developed first, or there is no fracture, but only an invisible stress concentration area. When the stress exceeds the rock limit, a fracture zone is formed. This stage is the initial stage of active fault development, and there is no obvious displacement in this stage, which is called embryo fracture or juvenile active fault. The existence of fault zone in this period is mainly manifested in the banded activity of small earthquakes.
The most vigorous development stage of active faults is its growth stage, and the external manifestation of faults is often a straight line with obvious displacement. Because of the similar nature of rock strata around faults, many faults exist in constituent systems. Such as syngenetic faults and NW-trending active faults on the edge of a series of graben or dustpan basins in North China; Some NW-trending active faults in Xinjiang and Gansu are in the growing period. During this period, the fault activity mode is relatively simple, and some moderate and strong earthquakes often occur at the ends of these outward-developing fault zones or where they intersect with other structures.
The mature stage of active fault development can be called active stage or mature stage. During this period, the fault zone often appears in the form of huge arc or wave extension, and is mostly formed by connecting several young active faults. During this period, the active mode of fault zone is complex, the displacement is large, the seismic activity of different active segments is different, and there is the phenomenon of migration and transformation of active segments. A series of giant strike-slip active faults in western China mostly belong to this development stage.
The last stage of the development of active faults can be called recession or old age. At this time, the fault activity is weak, obviously distorted and even cut by other structural features. During this period, the seismic activity on the fault zone is very low and the period is long. The Tanlu fault is the oldest active fault zone in eastern China, with the longest active history, the longest extension and the deepest crustal cutting. Through the analysis of satellite photos and deformation data, it can be seen that it was cut by a series of new NW-trending active faults. Individual strong earthquakes in the history of the Tan-Lu fault zone may be related to the activities of these small active fault systems, while the Tan-Lu fault zone only played a role in the structural conditions of the earthquake.
The fault activity has completely stopped. This fault has always been called a healing fault or a dead fault. At this time, there is no seismic activity on the fault.