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Kennebec River, Georgetown, MEVanessa Lyons
Sea Caves, La Jolla, CASamantha Bassman
Montmorency Falls, QCEmily Stuart
EARTHQUAKES
SEISMIC WAVES
EARTHQUAKES
SEISMIC WAVES
BODY WAVESBODY WAVES transmit energy through the Earth’s
interior in all directions from the earthquake’sfocus.
EARTHQUAKES
SEISMIC WAVES
BODY WAVES
Are the fastest seismic waves (6-7 km/sec).First to arrive at earthquake station and be
recorded on a seismograph.Energy is a compressional wave that alternates
between compression and dilation.Vibration is parallel to direction of travel.Produces sharp jolts.
PRIMARY or P-WAVES
EARTHQUAKES
SEISMIC WAVES
BODY WAVES
Slower than P-waves (3.5 km/sec).Second wave to arrive at earthquake station and
be recorded on a seismograph.Energy is up and down movement.Vibration is perpendicular to direction of travel.Produce continuous wriggling motion.Do not travel through liquid.
SECONDARY or S-WAVES
EARTHQUAKES
SEISMIC WAVES
SURFACE WAVES
Transmit energy along Earth’s surface.Causes the Earth’s surface to vibrate.Slowest of the seismic waves (2.5 km/sec).Two types: side to side whipping action
rolling up and down (i.e. ocean wave)Both can occur at the same time.Causes extensive damage to rigid structures.
EARTHQUAKES
SEISMIC WAVESSURFACE WAVES
EARTHQUAKES
MEASURING EARTHQUAKESMODIFIED MERCALLI INTENSITY SCALE
Earthquake strength depends on how much stored energy is released or INTENSITY.
Initially looked at destructiveness of earthquake.Can’t locate the epicenter accurately or measure
distance and actual intensity. Doesn’t consider quality of building vs. intensity.Can’t be used where no people live.Good to characterize historical earthquakes.Introduces a human component to earthquakes.
EARTHQUAKES
MEASURING EARTHQUAKES
EARTHQUAKES
MEASURING EARTHQUAKESRICHTER SCALE
Scale is based on MAGNITUDE, which is the amountof energy released by the earthquake.
Magnitude is the amplitude of the largest peak on theseismogram.
Really designed for use only in California.Works best for earthquakes of magnitude 7 or less.
The Richter scale is logarithmic, that is an increase of 1 magnitude unit represents a factor of ten times in amplitude.
The seismic waves of a magnitude 6 earthquake are 10 times greater in amplitude than those of a magnitude 5 earthquake.
However, in terms of energy release, a magnitude 6 earthquake is about 31X greater than a magnitude 5 and ~1000X greater than a 4.
EARTHQUAKES
MEASURING EARTHQUAKES
EARTHQUAKES
MEASURING EARTHQUAKESMOMENT-MAGNITUDE SCALE
Seismic moment more accurately gauges the total energy of a large earthquake.
MOMENT = (total length of fault rupture)X (depth of fault rupture)X (total amount of slip along rupture)X (strength of rock)
Produces MOMENT-MAGNITUDE scale.The longer the fault, the greater the earthquake.Allows direct measurement of quake related to its cause.
EARTHQUAKES
EARTHQUAKE DEPTH AND MAGNITUDEDEPTH
Related to depth of focus of the earthquake.Shallow focus = < 70 km (< 45 miles)Intermediate focus = 70-300 km (45-180 mi.)Deep focus = > 300 km (> 180 miles)
90% of all earthquakes have a focus < 100 km.Most occur within 60 km (40 mi) of Earth’s surface.Heat weakens rock with depth and rock loses its ability
to store strain energy.
EARTHQUAKES
EARTHQUAKE DEPTH AND MAGNITUDEDEPTH
Focus closer to surface allows greater brittle failure.1964 Good Friday Alaskan quake D = 33 km1994 Northridge, CA quake D = 21 km1989 Loma Prieta, CA quake D = 18 km
EARTHQUAKES
EARTHQUAKE DEPTH AND MAGNITUDEMAGNITUDE
Generally, earthquakes with shallower foci have greatermagnitude.
(Magnitude is the amount of energy released by the earthquake.)
EARTHQUAKES
EFFECTS OF EARTHQUAKES
GROUND DISPLACEMENT
Most obvious geologic effect of earthquakesSan Francisco 1906 earthquake had 7 m of
horizontal displacement.Anchorage 1964 Good Friday earthquake had
land going up 12 m and sea floor down 16 m.Anchorage earthquake was second largest
ever recorded.
EARTHQUAKES
EFFECTS OF EARTHQUAKES
GROUND DISPLACEMENT
1964 Anchorage Earthquake
1906 San Francisco Earthquake
EARTHQUAKES
EFFECTS OF EARTHQUAKES
LANDSLIDES AND LIQUEFACTION
Shaking and tremors dislodge unstable masses of rocksand soil on hillsides.
Fragments can be dislodged from bedrock andbuildings as well.
EARTHQUAKES
EFFECTS OF EARTHQUAKES
LANDSLIDES 1959 earthquake at Hebgen Lake, MT
1995 landslide in La Conchita, CA
EARTHQUAKES
EFFECTS OF EARTHQUAKES
FALLING DEBRIS
EARTHQUAKES
EFFECTS OF EARTHQUAKES
LIQUEFACTION
Conversion of unconsolidated material with some initial cohesiveness in to a mass of water-saturatedsediment that flows like a liquid, although nowater has been added.
Shaking increases the pressure on the water betweenthe sediment grains, forcing them apart
Loss of frictional contact produces a slurry of sedimentand mud
EARTHQUAKES
EFFECTS OF EARTHQUAKES
LIQUEFACTION
Turnagain Heights, AK1964
Government Hill Elementary SchoolAnchorage, AK, 1964
EARTHQUAKES
EFFECTS OF EARTHQUAKES
LIQUEFACTION
Kobe, Japan
EARTHQUAKES
EFFECTS OF EARTHQUAKES
LIQUEFACTION
Kobe, Japan
EARTHQUAKES
EFFECTS OF EARTHQUAKES
LIQUEFACTION
Port Royal, Jamaica1692
City slid 15 m belowsea level.
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