earthquake

Earthquake

Vibration of Earth produced by the rapid release of energy.

Focus

The source at depth from which energy radiates as seismic waves in all directions.

Epicenter

The surface location above the source (focus) of an earthquake.

Elastic Rebound Theory

The theory describing the process that leads to an earthquake, involving the bending of rock and subsequent snapping back.

Fault Creep

Gradual fault movement that releases little elastic energy, resulting in small earthquakes.

Stick-Slip Fault

A fault that locks and stores elastic energy for long periods, releasing it suddenly to produce large earthquakes.

Seismology

The study of earthquakes and seismic waves.

Seismograph

An instrument that measures seismic waves and records the movement of the Earth.

Surface Waves

Seismic waves that travel along the surface of the Earth and are the most destructive.

Body Waves

Seismic waves that travel through the Earth's interior, including P waves and S waves.

P Waves

Primary waves that compress and expand rock and can travel through solid and liquid.

S Waves

Secondary waves that change the shape of the material and cannot travel through liquid.

Lag Time

The time difference between the arrival of P waves and S waves used to locate the epicenter of an earthquake.

Triangulation

A method used to locate the epicenter of an earthquake using data from multiple seismograph locations.

Horizontal-Motion Seismograph

A type of seismograph that measures side-to-side movements.

Vertical-Motion Seismograph

A type of seismograph that measures up-and-down movements.

Foreshocks

Smaller earthquakes that occur days to years before a major earthquake.

Aftershocks

Smaller earthquakes that occur for days after the main earthquake.

Fault Scarp

A cliff formed by vertical offset along a fault.

Seismogram

The record provided by a seismograph that shows seismic wave activity.

Convergent Plate Boundaries

Regions where the majority of large earthquakes occur, comprising about 95% of energy released.

Divergent Plate Boundaries

Regions that have frequent, shallow, weak earthquakes.

Transform Faults

Faults that tend to generate large earthquakes.

San Andreas Fault

A well-known fault that moves approximately 3 cm per year, calculated from a 100-year offset.

Fault Offset

The distance that the fault has moved during an earthquake.

Primary Cause of Earthquakes

Slippage along fault lines.

Volcanic Eruption

One of the potential triggers of earthquakes.

Nuclear Blast

An event that can trigger an earthquake besides tectonic activity.

Elastic Energy

Energy stored in rock due to bending by tectonic forces.

Frictional Lock

Resistance holding rock together until slippage occurs.

Seismic Waves

The waves of energy released during an earthquake that radiate from the focus.

Deep Faults

Faults that may have no surface expression despite significant geological activity.

Magnitude Greater Than 5

Refers to significant earthquakes recorded between 1980 and 1990.

New Madrid Fault Zone

Site of notable earthquake activity within a continental plate with a major quake in 1811.

Inertia Principle

The principle on which seismographs operate, stating that objects at rest tend to stay at rest.

Seismic-Wave Travel-Time Graph

A graph that relates lag time to the distance from the epicenter.

Circum-Pacific Belt

One of the zones where the largest most destructive earthquakes originate.

Alpine-Himalayan Belt

Another major zone associated with high earthquake activity.

Energy Release from Earthquakes

The energy released during an earthquake that propagates as seismic waves.

Seismic Energy Distribution

How seismic energy is distributed along different fault types and plate boundaries.