Types of Faults to Know for Intro to Geology

Faults are fractures in the Earth's crust where blocks of rock move relative to each other. Understanding different types of faults—like normal, reverse, and strike-slip—helps explain how tectonic forces shape our planet's landscape and contribute to geological features.

1. Normal fault

   • Occurs when the crust is extended, causing one block of rock to move down relative to another.
   • Typically found in regions experiencing tectonic stretching, such as rift zones.
   • The hanging wall moves downward relative to the footwall.
   • Commonly associated with the formation of valleys and basins.

2. Reverse fault

   • Formed when the crust is compressed, causing one block of rock to move up relative to another.
   • The hanging wall moves upward relative to the footwall.
   • Often found in convergent plate boundaries where tectonic plates collide.
   • Can create mountain ranges and uplifted terrains.

3. Strike-slip fault

   • Characterized by horizontal movement of rock blocks past each other.
   • The movement is primarily lateral, with little vertical displacement.
   • Commonly associated with transform plate boundaries.
   • Can result in features like offset rivers and roads.

4. Thrust fault

   • A type of reverse fault with a low-angle fault plane.
   • The hanging wall is pushed up over the footwall due to compressional forces.
   • Often found in mountain ranges and areas of significant tectonic activity.
   • Can lead to the stacking of rock layers, creating complex geological structures.

5. Oblique-slip fault

   • Exhibits both vertical and horizontal movement, combining features of normal and strike-slip faults.
   • The movement can be a result of complex tectonic forces acting on the crust.
   • Common in regions where multiple stress regimes are present.
   • Can create varied geological features due to its mixed movement.

6. Transform fault

   • A specific type of strike-slip fault that occurs at plate boundaries.
   • Characterized by the lateral sliding of tectonic plates past one another.
   • Often associated with significant seismic activity and earthquakes.
   • Examples include the San Andreas Fault in California.

7. Listric fault

   • A curved fault that flattens with depth, often associated with normal faulting.
   • The hanging wall moves downwards along a curved surface.
   • Common in extensional tectonic settings, such as rift zones.
   • Can lead to the formation of large-scale geological structures like half-grabens.

8. Horst and graben

   • Horsts are elevated blocks of the Earth's crust, while grabens are down-dropped blocks.
   • Formed through extensional tectonics, often associated with normal faulting.
   • Commonly found in rift valleys and areas of crustal stretching.
   • The alternating pattern of horsts and grabens creates distinct topographical features.