Earthquakes

Intensity

A measure of the amount of ground shaking at a particular location based on observed property damage

Magnitude

Quantitative measurement of ground motion based on data from seismic records used to estimate the amount of energy released at an earthquake’s source

Modified Mercalli Intensity Scale

Based on property destruction in a region

Richter Magnitude Scale

Based on the amplitude of the largest seismic wave recorded

Moment magnitude

Measures the total energy released during an earthquake

Circum-Pacific Belt

More commonly known as the “Ring of Fire”. The zone of greatest seismic activity

Liquefaction

The phenomenon where loosely packed, waterlogged sediments behave as a fluid during the intense shaking of an earthquake

Seiches

Rhythmic sloshing of water in lakes, reservoirs and enclosed basins. Can be dangerous to small watercraft or if it causes spillage over the side

Tsunami

A series of large ocean waves, travel at 800 km/hr

Seismic gaps

Tectonically quiet zones along a fault where strain is currently building up

Paleoseismology

The study of prehistoric earthquakes

Deep focus earthquake

Earthquakes that result from stresses on, and brittle deformation of, a subducted plate

Earthquake

Ground shaking caused by the sudden and rapid movement of one block of rock sliding

Fault

Fractures in the crust

Focus/Hypocenter

Where rock slippage originates in the ground

Epicenter

The point on the ground surface directly above the focus

Seismic waves

Stored up energy the releases in all directions from the focus

Elastic rebound

Deformed rocks “snap back” to their original position

Aftershock

Numerous small earthquakes after a major earthquake

Foreshock

Minor earthquakes that sometimes precede a major earthquake by days, weeks, or months

Normal fault

Occur at divergent plate boundaries; minor earthquakes

Reverse and thrust faults

Occur at convergent plate boundaries; major earthquakes, tsunamis

Strike-slip fault

Occurs at transform plate boundaries; major earthquakes

Megathrust fault

Occur at subduction zones; strongest recorded earthquakes and tsunamis

Fault slip

The amount of displacement on the fault surface

Seismology

The study of earthquake waves

Seismograph/ seismometer

Devices that record the movement of Earth in relation to a stationary mass

Body waves

Waves that travel through Earth’s interior

Primary (P) waves

Compression waves; travel through all materials

Secondary (S) waves

Shear waves; only travel through solids

Surface waves

Waves that travel in rock layers just below Earth’s surface