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.