Earthquakes

Focus - the place within Earth where earthquake waves originate; scientists often refer to this as the hypocenter 

Epicenter - point on the surface directly above the focus/hypocenter

Seismic waves - acoustic waves (vibrations) caused by frictional slip along the fault plane and transmitted through the surrounding rock

Seismographs - machines that measure (seismometers) and record the seismic waves generated by earthquakes

Two types of seismic waves - body waves and surface waves

 Body waves - travel through earth’s interior

Two types of body waves - primary (p-waves) and secondary (S waves)

Surface waves - travel along earth’s surface, have the slowest velocity, include rayleigh and love waves

Rayleigh waves - roll counterclockwise from the direction of wave propagation

Love waves - sway side to side with no vertical motion

P waves - push pull (compressional) motion; travel through solids, liquids and gases; greatest velocity of all earthquake waves; ex: sound

S wave - also known as shear waves, travel only through solids, slower velocity than P waves

Order of earthquake - quake happens at time 0, then first p waves come, then S waves come, and surface waves come last.

Intensity - measure of the earthquake shaking at a given location based on amt. of damage; measured with modified mercalli intensity scale

Magnitude - measure of seismic wave amplitude (energy release), a function of distance from focus; introduced by Charles Richter

Shaking is amplified - on unconsolidated sediment and artificial fill

Eastern US - composed of strong bedrock 

Western US - relatively damaged rock from plate boundary tectonic forces

Richter magnitude scale - is no longer used by seismologists

Moment magnitude - the standard used by seismologists, and can measure very small to very large earthquakes

Megathrust earthquakes - largest, most destructive, and can generate tsunamis; there is a stuck area that ruptures and releases energy; tsunami starts during quake rupture

Earthquake hazards - ground shaking, liquefaction, tsunami, landslides and ground subsidence, fires

Liquefaction - spaces between soil grains filled with water, shaking destabilizes soil and buildings sink

Earthquake forecasting - estimates probability that EQ of certain magnitude will occur in a specific area during a specific time