In geology, the elastic-rebound theory is an explanation for how energy is released during an earthquake. Then they separate with a rupture along the fault; the sudden movement releases accumulated energy, and the rocks snap back almost to their original shape.

When the failure at the fault plane results in a violent displacement of the Earth’s crust, the elastic strain energy is released and seismic waves are radiated, thus causing an earthquake. This process of strain, stress, and failure is referred to as the Elastic-rebound theory.

Elastic rebound theory fits in well with the theory of plate tectonics and helps explains the cyclical nature of many earthquakes including why earthquakes repeatedly occur in the same regions.

The focus is the place inside Earth’s crust where an earthquake originates. The point on the Earth’s surface directly above the focus is the epicenter. When energy is released at the focus, seismic waves travel outward from that point in all directions.

The world’s greatest earthquake belt, the circum-Pacific seismic belt, is found along the rim of the Pacific Ocean, where about 81 percent of our planet’s largest earthquakes occur. It has earned the nickname “Ring of Fire”.

Buildings may sway, tilt, or collapse as the surface waves pass. Ground shaking from earthquakes can collapse buildings and bridges; disrupt gas, electric, and phone service; and sometimes trigger landslides, avalanches, flash floods, fires, and huge, destructive ocean waves (tsunamis).

PHIVOLCS Earthquake Intensity Scale (PEIS)

Intensity scales. The Richter scale measures the magnitude of earthquakes, and the Mercalli scale measures their intensity. The violence of seismic shaking varies considerably over a single affected area.

Intensity can be found by taking the energy density (energy per unit volume) at a point in space and multiplying it by the velocity at which the energy is moving. The resulting vector has the units of power divided by area (i.e., surface power density).

The five categories are Media/Seat, Daily Activity, Base, Heart Health and Max. Media/Seat (1) includes time spent sitting down in which a person can talk with no effort. Daily Activity (2) includes activities that are low in intensity and easy to perform.

The amplitude of a wave is related to the amount of energy it carries. The average amount of energy passing through a unit area per unit of time in a specified direction is called the intensity of the wave. As the amplitude of the sound wave increases, the intensity of the sound increases.