earthquakes

where do eqs happen

95% along plate boundaries

shallow depth

<70km (divergent and transform)

deep focus

>70 km (convergent)

stress

force acting on crustal rocks that causes rock to be deformed - movement of Earth occurs when stress on rocks is greater than the strength of rocks

compression stress

decreases material volume (squeezes)

tension stress

pulls material apart

shear stress

different parts of material moved in different directions

strain

deformation of material in response to stress

elastic deformation

when material is compressed, bent, or stretched; occurs under low stress; rock returns to original state when stress is gone

plastic deformation

strain that produces permanent damage, 

fault

crack in Earth’s crust along which rock has moved

elastic rebound

release of strain energy as rocks move along fault

What happens when rocks are deformed by stress?

strain energy builds up and energy can be released if stress large enough to overcome the strength of the rocks

seismic waves

vibrations of the ground produced during an eq

epicenter

point on Earth’s surface above the focus

-surface waves originate here

focus

point where body waves originate

primary wave (p wave)

squeeze and push rocks in the same direction that the waves are traveling; fastest waves, travel through solids and liquids

secondary wave (s wave)

moves at right angles (up and down) to the direction of the wave; named for arrival time; slower than p waves, only travel through solids

surface waves

only on earth’s surface, slowest type of wave; usually the most destructive- cause the most movement of the ground and take the longest time to pass

rayleigh wave

move up and down

long wave

move side to side

mercalli scale

qualitative observation; measured based on the intensity of eq

ritcher scale

quantitative, numerical measurement of magnitude of eq (amplitude - energy)

seismometer

instrument used to measure motion of the ground during an earthquake

seismograph

record produced by a seismometer