GEOL 4

Aftershock

A smaller earthquake that follows the mainshock, occurring in the same region as the initial quake.

Amplification

The increase in seismic wave amplitude as they pass through softer ground, leading to stronger shaking.

Anticline

An upward-arching fold in rock layers, typically formed by compressional forces.

Attenuation

The decrease in seismic wave energy as it travels through the Earth’s materials.

Body Waves

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

Compression

A type of stress that squeezes rocks together, often leading to faulting or folding.

Dip-Slip Fault

A fault where movement occurs along the dip of the fault plane, either upward (reverse fault) or downward (normal fault).

Earthquake

The shaking of the Earth's surface caused by the sudden release of energy along a fault.

Elastic Rebound

The process where rocks deform under stress and then snap back to their original shape, releasing energy and causing an earthquake.

Epicenter

The point on the Earth's surface directly above the earthquake's focus.

Fault

A fracture in the Earth's crust along which movement has occurred.

Focus

The point within the Earth where an earthquake originates.

Folds

Bends in rock layers caused by compressional forces.

Footwall

The block of rock below a fault plane.

Foreshock

A smaller earthquake that precedes the mainshock.

Hanging Wall

The block of rock above a fault plane.

Intensity

A measure of the effects of an earthquake at different locations, often determined using the Modified Mercalli Intensity scale.

Intraplate

Earthquakes that occur within a tectonic plate, rather than at plate boundaries.

Liquefaction

The process where saturated soil temporarily loses strength due to shaking, behaving like a liquid.

Magnitude

A numerical measure of an earthquake’s size based on energy release.

Mainshock

The largest earthquake in a sequence, often followed by aftershocks.

Modified Mercalli Intensity (MMI)

A scale that measures earthquake intensity based on observed effects and damage.

Moment Magnitude

A modern scale used to measure earthquake size, based on seismic moment (fault slip, area, and rock rigidity).

Normal Fault

A dip-slip fault where the hanging wall moves downward relative to the footwall, caused by tension.

P-Waves (Primary Waves)

The fastest seismic waves that travel through solids, liquids, and gases by compressing and expanding the material.

Resonance

The amplification of shaking when the frequency of seismic waves matches the natural frequency of a structure.

Reverse Fault

A dip-slip fault where the hanging wall moves upward relative to the footwall, caused by compression.

Richter Scale

An older logarithmic scale that measures earthquake magnitude based on seismic wave amplitude.

Rupture

The breaking and displacement of rock along a fault during an earthquake.

S-Waves (Secondary Waves)

Seismic waves that move perpendicular to their direction of travel; they only move through solids.

Scarp

A steep slope or cliff formed by fault movement or erosion.

Seismometer

An instrument that detects and records seismic waves.

Shear

A type of stress that causes parts of a material to slide past each other in opposite directions.

Strain

The deformation of rocks due to stress.

Stress

The force applied to a material, which can cause deformation and lead to earthquakes.

Strike-Slip Fault

A fault where horizontal motion occurs due to shear stress, such as the San Andreas Fault.

Subsidence

The sinking or downward settling of the Earth’s surface.

Surface Waves

Seismic waves that travel along the Earth's surface, causing most earthquake damage.

Syncline

A downward-curving fold in rock layers.

Tectonic Creep

The slow, continuous movement along a fault without noticeable earthquakes.

Tension

A type of stress that pulls rocks apart, leading to normal faulting.

Tsunami

A large ocean wave generated by underwater earthquakes, landslides, or volcanic eruptions.

Warning

A system that detects early seismic waves and alerts people before strong shaking arrives.