EARTHQUAKE🫡😩

Stress

Forces per unit area that act on a material -- compression, tension, and shear.

Strain

Deformation of materials in response to stress.

Elastic Deformation

Causes materials to bend and stretch; proportional to stress, so if the stress is reduced or returns to zero the strain or deformation is reduced or disappears.

Plastic Deformation

Permanent deformation caused by strain when stress exceeds a certain value.

Fault

Fracture or system of fractures in Earth's crust that occurs when stress is applied too quickly or stress is too great; can form as a result of horizontal compression (reverse fault), horizontal shear (strike-slip fault), or horizontal tension (normal fault).

Seismic Wave

The vibrations of the ground during an earthquake.

Primary Wave

Seismic wave that squeezes and pushes rocks in the same direction that the wave travels, known as a P-wave.

Secondary Wave

Seismic wave that causes rock particles to move at right angles to the direction of the wave, known as an S-wave.

Focus

Point of initial fault rupture where an earthquake originates that usually lies at least several kilometers beneath the Earth's surface.

Epicenter

Point on Earth's surface directly above the focus of an earthquake.

Seismometer

Instrument used to measure horizontal or vertical motion during an earthquake.

Richter Scale

Numerical rating system used to measure the amount of energy released during an earthquake.

Magnitude

Measure of the energy released during an earthquake, which can be described using the Richter Scale.

Amplitude

The size of the seismic waves; an increase of 1 in the scale represents an increase in amplitude of a factor of 10.

Moment Magnitude Scale

Scale used to measure earthquake magnitude—taking into account the size of the fault rupture, the rocks' stiffness, and amount of movement along the fault—using values that can be estimated from the size of several types of seismic waves.

Modified Mercalli Scale

Measures earthquake intensity on a scale from I to XII; the higher the number, the greater the damage the earthquake has caused.

Tsunami

Large, powerful ocean wave generated by the vertical motions of the seafloor during an earthquake; in shallow water, can form huge, fast-moving breakers exceeding 30 m in height that can damage coastal areas.

Soil Liquefaction

Process associated with seismic vibrations that occur in areas of sand that is nearly saturated; resulting in the ground behaving like a liquid.

Seismic Gap

Place along an active fault that has not experienced an earthquake for a long time.

Seismogram

Record produced by a seismometer that can provide individual tracking of each type of seismic wave.