ESC 102- Earthquakes

earthquake

vibration generated from sudden release of energy associated with rapid movement of rock along a FAULT

fault

ruptures/breaks that divide crust into "blocks" (units of rock that move relative to the other block)

what causes the "shake"?

when stress applied, rocks stretch. rocks can snap back or rupture, rupturing causes vibration.

elastic deformation

reversible deformation in a rock

returns to original shape. does not rupture

elastic rebound

the sudden snapping back of elastically deformed rock to its undeformed shape

epicenter

location on earths surface directly above focus

fault surface

fracture surface between one block and another. movement occurs

focus

origin of earthquake within earths crusy where movement first occurs

seismic waves

waves of energy that travel like shock waves from focus to surrounding area

p waves

primary body wave. compresses and expands the ground. arrive first

s wave

secondary body wave. moves the ground up and down or side to side

Rayleigh wave

surface wave behaves like a rolling ocean wave and causes the ground to move in an elliptical path.

love wave

A surface wave that causes rocks to move side-to-side. Very Destructive.

seismometer and seismographs

seismometer detects seismic waves and recorded on a paper or electronic trace- seismogram

main shock

biggest earthquake in cluster

foreshock

before main shock

aftershock

after main shock

how to know where earthquake occured

1) time difference from arrival of body wave and surface wave

2) drawing on map a circle with radius = distance to epicenter for 3 stations. intersection = epicenter.

earthquake magnitude

energy released. intensity refers to effects on society

Moment Magnitude Scale

replaced richter scale. numbers similar but more accurate for large earthquakes

used by seimsologists- quantitative

Modified Mercalli intensity scale and peak ground acceleration

-qualitative

-not tecnhically a scale, used by engineers, quantitative, site specific

Richter calculated based on:

difference in P and S arrival times and maximum amplitude on seismograph.

not accurate for large, deep or faraway earthquakes

Moment magnitude how measured

based on energy released, more precise for large earthquakes, based on seismograph measurements and fault displacement

earthquakes and divergent

shallow 30km

earthquakes and convergent

shallow to deep 700km

strike slip fault tension

shearing tension (pulling opposite directions, perp to plane)

normal fault tension/compression

tension. see it at divergent plate boundary

thrust fault compression/tension?

low angle reverse faults. compression (at convergent boundary)

reverse fault tension or compression?

compression (convergent)

modified mercalli intensity scale

observations and perceptions of people who felt earthquake.

12 degrees of intensity. qualitative