E&E 151 S Introductory Geology: Chapters 16.1 - 16.5 (Earthquakes Pt. 1) Definitive Study

Earthquake

A trembling of the ground caused by the sudden release of energy stored in rocks beneath the surface.

Stress

Tectonic forces deep in the Earth that push or pull on rocks.

Strain

The bending or changing of shape in rocks due to tectonic stress.

Elastic Rebound Theory

The classic explanation for earthquakes stating that tectonic forces act on rocks over many decades, causing them to bend and store energy until they break suddenly along a fault, releasing energy as seismic waves.

Seismic Waves

Waves of energy released when rock breaks, causing the ground to tremble.

Seismometer

An instrument that measures seismic waves by using inertia to keep a heavy suspended mass as motionless as possible while its frame moves with the ground.

Seismograph

A seismometer equipped with a recording device to produce a permanent record of vibrations.

Seismogram

The permanent record of Earth's vibrations produced by a seismograph.

Shallow-Focus Earthquakes

Earthquakes occurring 0–70 km deep, which are the most common and account for 85% of total quake energy released.

Intermediate-Focus Earthquakes

Earthquakes occurring 70–350 km deep.

Deep-Focus Earthquakes

Earthquakes occurring 350–670 km deep.

Intensity

A measure of an earthquake's effect on people and buildings, determining the amount and type of damage caused.

Modified Mercalli Scale

A scale using Roman numerals from I to XII to express earthquake intensity based on observed damage.

Magnitude

A calculated number representing the amount of energy released by an earthquake.

Richter Scale

A historical, open-ended logarithmic scale used to report earthquake magnitude, where an increase of one whole number means a tenfold increase in vibration amplitude and roughly 32 times the energy released.

Moment Magnitude

A more objective measurement scale for large earthquakes determined from rock strength, rupture surface area, and the amount of rock displacement along the fault.

Circum-Pacific Belt

A narrow geographic belt encircling the Pacific Ocean where approximately 80% of shallow, 90% of intermediate, and nearly 100% of deep-focus earthquakes occur.

Mediterranean-Himalayan Belt

Another major earthquake concentration running through the Mediterranean Sea, the Mideast, the Himalayas, and the East Indies.

Ground Motion

The trembling and shaking of the land that causes buildings to vibrate and potentially collapse.

Liquefaction

A special type of ground failure where water-saturated soil or sediment turns from a solid to a liquid due to earthquake shaking, causing buildings to sink or tanks to float.

Foreshocks

Small earthquakes that precede a main shock.

Aftershocks

Smaller earthquakes that follow the main shock and can cause significant damage to already weakened structures.

Resonance

A phenomenon where a building is pushed to vibrate in time with the underlying sediment's natural period, amplifying earthquake waves and leading to structural collapse.

Tsunami (Seismic Sea Waves)

Very large sea waves generated by the sudden upward or downward movement of the sea floor during a submarine earthquake, submarine landslide, or volcanic explosion.