How to distinguish between reverse faults and normal faults? In geology, reverse faults and normal faults are two common types of faults. Their distinction is mainly based on the relative movement direction of the two plates of the fault and the tectonic environment in which they are formed. The following is a detailed explanation from the aspects of core characteristics, formation mechanism, typical characteristics, etc.:

  I. Core distinction: relative movement direction of the two plates

   1. Normal fault: The upper plate (the rock block located above the fault plane) slides downward relative to the lower plate (the rock block located below the fault plane). In simple terms, the upper plate descends and the lower plate rises relatively.

   2. Reverse fault: The upper plate slides upward relative to the lower plate. In simple terms, the upper plate rises and the lower plate descends relatively.

   II. Formation mechanism and stress environment

   1. Normal fault

   ① Stress: tensile stress;

   ② Tectonic environment: often seen in crustal stretching areas, such as rifts (East African Rift Valley) and plate discrete boundaries (mid-ocean ridges).

   2. Reverse fault

   ① Stress: subject to compression stress;

   ② Tectonic environment: often found in crust compression areas, such as plate collision zones (Himalayas) and orogenic belt fold tectonic zones.

  III. Typical characteristics and identification marks

   1. Fault plane dip

   ① Normal fault: The fault plane is usually steep, with a dip angle of more than 45° (some may become slower due to later transformation).

   ② Reverse fault: The fault plane dip angle varies greatly, among which reverse faults with a dip angle of less than 30° are specifically called "thrust faults" (common in strong compression zones, such as the edge of the Qinghai-Tibet Plateau).

  2. Associated structures

   ① Normal fault: often forms grabens (rock blocks sink between two normal faults) and horsts (rock blocks rise between two normal faults), such as the Fenwei graben.

   ② Reverse fault: often accompanied by strong fold structures (formed by compression), and the upper plate often has a crushed zone where the rock is squeezed and crushed, and the lower plate may have traction folds (the rock layer is dragged and bent).

   3. Surface performance

   ① Normal fault: easy to form steep cliffs and canyons, and the thickness of the rock layers on both sides of the fault may become thinner due to stretching.

   ② Reverse fault: easy to form mountains, thrust mats (rocks in the upper plate are pushed onto the lower plate), and even flying peaks (isolated rock blocks that are pushed) and structural windows (local exposure of rocks in the lower plate).

   4. Summary: Quick distinction formula

   ① Normal fault: tension environment, upper plate descending, steep inclination, accompanied by graben horsts.

   ② Reverse fault: compression environment, upper plate rising, gentle inclination (thrust), accompanied by fold thrust.

   By observing the direction of rock block movement, force environment and associated structures, the two can be accurately distinguished.

   Normal faults and reverse faults are the "unity of opposites" of crustal movement. The former stretches and the latter compresses, together shaping the mountain and river pattern on the earth's surface. Field identification requires comprehensive stratigraphic sequence, structural features and topographic evidence, with particular attention to the core role of the upper plate movement direction and dip parameters. Accurate identification of the two types of faults is not only the basis for geological mapping, but also the key basis for resource exploration and earthquake risk assessment.