Inactive faults can become active again. In our case there are no signs of that, although UP seismologists remain observant. This diagram shows an earthquake along a fault. Active Faults are those faults that are still subject to Earthquakes, those that are hazards.

Earthquakes can also occur far from the edges of plates, along faults. Faults are cracks in the earth where sections of a plate (or two plates) are moving in different directions. Faults are caused by all that bumping and sliding the plates do. They are more common near the edges of the plates.

A fault is a fracture or zone of fractures between two blocks of rock. Faults allow the blocks to move relative to each other. This movement may occur rapidly, in the form of an earthquake – or may occur slowly, in the form of creep.

San Andreas fault

All the faults on Earth are not active. When the stress conditions evolve, faults get deactivated or reactivated. Major faults are mainly found at the boundaries between tectonic plates, but active faults also exist within tectonic plates.

In a reverse fault, the block above the fault moves up relative to the block below the fault. This fault motion is caused by compressional forces and results in shortening. A reverse fault is called a thrust fault if the dip of the fault plane is small.

There are three kinds of faults: strike-slip, normal and thrust (reverse) faults, said Nicholas van der Elst, a seismologist at Columbia University’s Lamont-Doherty Earth Observatory in Palisades, New York.

There are two types of inclined dip slip faults. In Normal faults the hanging wall in moving downward relatively to the footwall. Normal faults accommodate extensional deformation. In reverse faults, the hanging wall in moving upward relatively to the footwall.

Answer: A fault, which is a rupture in the earth’s crust, is described as a normal fault when one side of the fault moves downward with respect to the other side. The opposite of this, in which one side moves up, is called a reverse fault.

A reverse fault is a dip-slip fault in which the hanging-wall has moved upward, over the footwall. Reverse faults are produced by compressional stresses in which the maximum principal stress is horizontal and the minimum stress is vertical.

An aftershock can cause damage days or months after a large earthquake. The correct answer is D, an aftershock.

This is called confining stress. Compression squeezes rocks together, causing rocks to fold or fracture (break) (figure 1). Compression is the most common stress at convergent plate boundaries. Rocks that are pulled apart are under tension.

The stress that squeezes something. It is the stress component perpendicular to a given surface, such as a fault plane, that results from forces applied perpendicular to the surface or from remote forces transmitted through the surrounding rock.

Since the rock cannot move, it cannot deform. This is called confining stress. Compression squeezes rocks together, causing rocks to fold or fracture (break) (Figure below). Compression is the most common stress at convergent plate boundaries.