EarthquakesEarthquakes

Earthquakes - The movement of the ground, caused by - The movement of the ground, caused by waves of energy released as rocks move waves of energy released as rocks move along faultsalong faults

Fault – a large fracture in rocks, from Fault – a large fracture in rocks, from several meters to many kilometers long, several meters to many kilometers long, where rocks not only crack but also move where rocks not only crack but also move along either side of the breakalong either side of the break

Types of Stresses; tension, compression, & Types of Stresses; tension, compression, & shearshear

Types of Faults; Normal, Reverse, Types of Faults; Normal, Reverse, Strike-SlipStrike-Slip

Earthquake Mechanics Earthquake Mechanics (cont.)(cont.)

Epicenter – the point on Earth’s surface Epicenter – the point on Earth’s surface directly above the earthquake’s focusdirectly above the earthquake’s focus

Focus – the point in Earth’s interior or Focus – the point in Earth’s interior or where movement releases energy to where movement releases energy to cause the earthquakecause the earthquake

Seismic wavesSeismic waves: :

Waves of vibration caused by the energy Waves of vibration caused by the energy released during an earthquake. released during an earthquake.

• Types of waves produced: Surface and body Types of waves produced: Surface and body waveswaves

• SeismographSeismograph: is the instrument used to : is the instrument used to detect, measure, and record seismic waves detect, measure, and record seismic waves produced by earthquakes. produced by earthquakes.

• MagnitudeMagnitude - A measure of the strength of an - A measure of the strength of an earthquake or strain energy released by it, as earthquake or strain energy released by it, as determined by seismographic observations. determined by seismographic observations.

• SeismogramSeismogram: the recording of an earthquake : the recording of an earthquake made by a seismograph made by a seismograph

Body WavesBody WavesP waves – Primary Wave:P waves – Primary Wave:

compression & expansion - push-pull seismic waves • sound waves (too low to be heard)• fastest (~8 to 9 km/sec) depending on material• first to be recorded at a seismograph• causes rock particles to vibrate in the same direction the wave is

traveling• denser the material, the faster the P-wave travels

http://www.youtube.com/watch?v=2rYjlVPU9U4

Body WavesBody WavesS waves – Secondary Wave:S waves – Secondary Wave:• shearingshearing (lateral; side to side) seismic waves (lateral; side to side) seismic waves• travels through solid only (3 to 5 km/sec) - NOT travels through solid only (3 to 5 km/sec) - NOT

liquid or gassesliquid or gasses• second to reach and be recorded at a seismographsecond to reach and be recorded at a seismograph• causes the rock particles to vibrate at right angles causes the rock particles to vibrate at right angles

to the direction of travelto the direction of travel

• http://www.youtube.com/watch?v=gl4FvHKzAlU http://www.youtube.com/watch?v=gl4FvHKzAlU

Surface WavesSurface WavesSurface Waves – waves of energy, released

during an earthquake, that reach Earth’s surface and travel outward from the epicenter in all directions ON THE SURFACE ONLY

Travels only through solid

Surface WavesSurface WavesL wave – Love wave:L wave – Love wave:• shearingshearing (lateral; side to side) seismic waves (lateral; side to side) seismic waves• speed is 2 to 6 km/secspeed is 2 to 6 km/sec• has the greatest height of the ‘waves’ has the greatest height of the ‘waves’

recorded on recorded on a seismograma seismogram• has a horizontal (side to side) motion that is has a horizontal (side to side) motion that is

perpendicular to the direction of travelperpendicular to the direction of travel• causes the most destructioncauses the most destruction• (named after A.E.H. Love, the English (named after A.E.H. Love, the English

mathematician who discovered it.)mathematician who discovered it.)

Surface WavesSurface WavesRayleigh wave (Surface wave):Rayleigh wave (Surface wave):• Slowest of the waves 1 to 5 km/secSlowest of the waves 1 to 5 km/sec• Most complex of earthquake waves; elliptical Most complex of earthquake waves; elliptical

motion at the Earth's surface.motion at the Earth's surface.• They are usually felt as a rolling or rocking They are usually felt as a rolling or rocking

motionmotion• In the case of major earthquakes, can be In the case of major earthquakes, can be

seen as they approach seen as they approach • Often the largest and most destructive, of the Often the largest and most destructive, of the

wave types caused by an earthquake.wave types caused by an earthquake.• Named after Lord Rayleigh, the English Named after Lord Rayleigh, the English

physicist who predicted its existence.physicist who predicted its existence.

Surface WavesSurface Waves• Love waves – L-wavesLove waves – L-waves

• Rayleigh wavesRayleigh waves

Earthquake MachinesEarthquake MachinesSeismograph – instrument that detects Seismograph – instrument that detects

& records earthquake seismic waves& records earthquake seismic waves

Seismogram – the recording data Seismogram – the recording data sheet of an earthquake made by a sheet of an earthquake made by a seismographseismograph

http://www.leo.lehigh.edu/projects/seismic/graphics/012601_SIndia.jpg

Earthquake IntensityEarthquake Intensity

• Modified Mercalli Scale – intensity scale (modified for North American conditions); composed of 12 increasing levels of intensity that range from imperceptible shaking to catastrophic destruction.

http://www.abag.ca.gov/bayarea/eqmaps/doc/mmi.htmlhttp://www.abag.ca.gov/bayarea/eqmaps/doc/mmi.html • Seismic moment - measures the earthquake’s

strength, or the energy released based the amount of displacement along a fault.

Earthquake IntensityEarthquake Intensity

• Richter ScaleRichter Scale - - – measures the strength of an earthquakemeasures the strength of an earthquake– increase of one unit of magnitude (for increase of one unit of magnitude (for

example, from 4.6 to 5.6) represents a 10-fold example, from 4.6 to 5.6) represents a 10-fold increase in wave amplitude on a seismogramincrease in wave amplitude on a seismogram

– or approximately a or approximately a 32-fold increase in the 32-fold increase in the energyenergy released. released.

ThereforeTherefore a magnitude 6.7 earthquake a magnitude 6.7 earthquake releases over 900 times (32 times 32) the releases over 900 times (32 times 32) the energy of a 4.7 earthquake. energy of a 4.7 earthquake.

Creation of a Tsunami

Essential Questions -- Earthquakes• Name and describe the 3 different seismic waves• Explain how the structure of the earth’s interior

affects seismic waves• Describe how seismographs are used to determine

the epicenter of an earthquake• List the different scales used to measure the

magnitude and intensity of an earthquake• Discuss the relationship between earthquakes and

tsunamis• Identify the three types of stress and the resultant

features (faults/folds) associated with each.