EARTHQUAKES sudden movement or shaking of the Earth sudden movement or shaking of the Earth Caused by:Caused by: –plate tectonic stresses (stick-slip)

EARTHQUAKESEARTHQUAKES sudden movement or shaking of the Earthsudden movement or shaking of the Earth

• Caused by:Caused by:

– plate tectonic stresses (stick-slip)plate tectonic stresses (stick-slip)

• Located at:Located at:

– plate boundariesplate boundaries

• Resulting in:Resulting in:

– breaks in Earth’s crust (faults)breaks in Earth’s crust (faults)

TERMINOLOGYTERMINOLOGY• The The FOCUSFOCUS is the place within the Earth and is the place within the Earth and

along the fault where rupture occursalong the fault where rupture occurs• The The EPICENTEREPICENTER is the geographic point on the is the geographic point on the

surface directly above the focus surface directly above the focus • WAVES are produced WAVES are produced

by the release by the release of energyof energy

EARTHQUAKE EARTHQUAKE WAVESWAVES waves that spread out and carry energy in waves that spread out and carry energy in

all directions from the focusall directions from the focus• P waveP wave = primary; push; fast. = primary; push; fast.• S waveS wave = secondary; snake; slow. = secondary; snake; slow.

EARTHQUAKE EARTHQUAKE WAVESWAVES

MEASURING EARTHQUAKESMEASURING EARTHQUAKES

• Seismographs record earthquake wavesSeismographs record earthquake waves

• Seismograms show:Seismograms show:– Arrival of P & S wavesArrival of P & S waves– Distance to the Distance to the

epicenterepicenter

HOW TO READ HOW TO READ SEISMOGRAMSSEISMOGRAMS

HOW TO READ HOW TO READ SEISMOGRAMSSEISMOGRAMS• Time between arrival of P waves and S Time between arrival of P waves and S

waves shows distance from epicenterwaves shows distance from epicenter

MINI-QUIZ #1MINI-QUIZ #1

1.1. Which type of seismic waves are fastest? Which type of seismic waves are fastest? P WAVESP WAVES

2.2. What does the difference in time between P What does the difference in time between P and S waves tell you?and S waves tell you?THE STATION’S DISTANCE TO THE EPICENTERTHE STATION’S DISTANCE TO THE EPICENTER

EARTHQUAKE EARTHQUAKE MAGNITUDEMAGNITUDE quantitativequantitative value that measures the energy value that measures the energy

released by the earthquakereleased by the earthquake

The The Richter ScaleRichter Scale– From <2 to ~10From <2 to ~10– LogarithmicLogarithmic scale (grows exponentially; scale (grows exponentially;

+ 1 on the scale = x10 in wave amplitude)+ 1 on the scale = x10 in wave amplitude)– Does not change for a specific earthquake.Does not change for a specific earthquake.

What you need:What you need:– AmplitudeAmplitude (wave height) (wave height)– Time between 1Time between 1stst P and 1 P and 1stst S waves S waves distance distance

Richter Scale is logarithmic

1 magnitude = too small to feel2 = 10x bigger3= 100x4= 1000x5= 10,000x6= 100,000x7= 1,000,000x8= 10,000,000x9= 100,000,000x10= 1,000,000,000x bigger than

a 1 magnitude earthquake

Northridge, 1994 = 6.7Northridge, 1994 = 6.7

Indonesia (tsunami), 2004 = Indonesia (tsunami), 2004 = 9.09.0

Pakistan, 2005 = 7.6Pakistan, 2005 = 7.6

Haiti, 2010 = 7.0Haiti, 2010 = 7.0

Chile, 2010 = 8.8Chile, 2010 = 8.8

Biggest EVER (since 1900) = Biggest EVER (since 1900) = Chile, 1960 = 9.5Chile, 1960 = 9.5

Biggest in US = AK, 1964 = Biggest in US = AK, 1964 = 9.29.2

MINI-QUIZ #2MINI-QUIZ #2

1.1. Which scale is used to measure magnitude?Which scale is used to measure magnitude?RICHTER SCALERICHTER SCALE

2.2. What is the amplitude of a wave?What is the amplitude of a wave?THE HEIGHT OF A WAVETHE HEIGHT OF A WAVE

3.3. How do you determine magnitude?How do you determine magnitude?USE THE AMPLITUDE AND THE TIME USE THE AMPLITUDE AND THE TIME

DIFFERENCE BETWEEN THE 1DIFFERENCE BETWEEN THE 1STST P WAVE AND P WAVE AND 11STST S WAVE S WAVE

Magnitude vs. Amplitude

MagnitudeThe same value for the entire earthquake; constant.You need:

a) amplitude b) Ts-Tp (distance)

AmplitudeAmplitude

Changes with -- Changes with --

a)a) Distance (Decreases as you go further away from the focus)Distance (Decreases as you go further away from the focus)

b)b) Geology (depends on what material the earthquake is Geology (depends on what material the earthquake is travelling through).travelling through).

EARTHQUAKE EARTHQUAKE INTENSITYINTENSITY

qualitativequalitative description of description of the effect of shaking, the effect of shaking, based on damage to natural and humanly based on damage to natural and humanly made structuresmade structures

• The Modified The Modified Mercalli ScaleMercalli Scale– From I to XII (Roman numerals)From I to XII (Roman numerals)

– Descriptive, changes with distance from Descriptive, changes with distance from epicenterepicenter

• What you need:What you need:– Your senses!Your senses!

MERCALLI VS. RICHTERMERCALLI VS. RICHTER

ISOSEISMAL MAPSISOSEISMAL MAPS shows area of equal earthquake intensityshows area of equal earthquake intensity,

connecting areas with the same Mercalli value.

MINI-QUIZ #3MINI-QUIZ #3

1.1. Which scale is used to measure intensity?Which scale is used to measure intensity?MODIFIED MERCALLI SCALEMODIFIED MERCALLI SCALE

2.2. What would change an earthquake’s What would change an earthquake’s intensity?intensity?

A) GEOLOGY, OR B) DISTANCEA) GEOLOGY, OR B) DISTANCE

Earthquake HazardsEarthquake Hazards LIQUEFACTIONLIQUEFACTION = = soils or sand is “saturated” --the space between individual particles is completely filled with water; then the soil shakes, and the solid acts like a liquid

LIQUEFACTIONLIQUEFACTION

Earthquake HazardsTSUNAMI= underwater earthquake causing

massive displacement of water

http://www.pbs.org/wnet/savageearth/animations/tsunami/index.html