Earthquakes

Earthquakes - The movement of the ground, caused by waves of energy released as rocks move along faults Fault – a large fracture in rocks, from several meters to many kilometers long, where rocks not only crack but also move along either side of the break Types of Stresses; tension, compression, & shear Types of Faults; Normal, Reverse, Strike-Slip Types of Faults; Normal, Reverse, Strike-Slip

Earthquake Mechanics (cont.) Epicenter – the point on Earth’s surface directly above the earthquake’s focus Focus – the point in Earth’s interior or where movement releases energy to cause the earthquake

Seismic waves: Waves of vibration caused by the energy released during an earthquake. Types of waves produced: Surface and body wavesTypes of waves produced: Surface and body waves Seismograph: is the instrument used to detect, measure, and record seismic waves produced by earthquakes.Seismograph: is the instrument used to detect, measure, and record seismic waves produced by earthquakes. Magnitude - A measure of the strength of an earthquake or strain energy released by it, as determined by seismographic observations.Magnitude - A measure of the strength of an earthquake or strain energy released by it, as determined by seismographic observations. Seismogram: the recording of an earthquake made by a seismographSeismogram: the recording of an earthquake made by a seismograph

Body Waves 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

Body Waves S waves – Secondary Wave: shearing (lateral; side to side) seismic wavesshearing (lateral; side to side) seismic waves travels through solid only (3 to 5 km/sec) - NOT liquid or gassestravels through solid only (3 to 5 km/sec) - NOT liquid 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 to the direction of travelcauses the rock particles to vibrate at right angles to the direction of travel

Surface Waves Surface 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 Waves L wave – Love wave: shearing (lateral; side to side) seismic wavesshearing (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’ recorded on a seismogramhas the greatest height of the ‘waves’ recorded on a seismogram has a horizontal (side to side) motion that is perpendicular to the direction of travelhas a horizontal (side to side) motion that is perpendicular to the direction of travel causes the most destructioncauses the most destruction (named after A.E.H. Love, the English mathematician who discovered it.)(named after A.E.H. Love, the English mathematician who discovered it.)

Surface Waves 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 motion at the Earth's surface.Most complex of earthquake waves; elliptical motion at the Earth's surface. They are usually felt as a rolling or rocking motionThey are usually felt as a rolling or rocking motion In the case of major earthquakes, can be seen as they approachIn the case of major earthquakes, can be seen as they approach Often the largest and most destructive, of the wave types caused by an earthquake.Often the largest and most destructive, of the wave types caused by an earthquake. Named after Lord Rayleigh, the English physicist who predicted its existence.Named after Lord Rayleigh, the English physicist who predicted its existence.

Surface Waves Love waves – L-wavesLove waves – L-waves Rayleigh wavesRayleigh waves

Earthquake Machines Seismograph – instrument that detects & records earthquake seismic waves Seismogram – the recording data sheet of an earthquake made by a seismograph

Earthquake 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. Seismic moment - measures the earthquake’s strength, or the energy released based the amount of displacement along a fault.

Earthquake Intensity Richter Scale -Richter Scale - –measures the strength of an earthquake –increase of one unit of magnitude (for example, from 4.6 to 5.6) represents a 10-fold increase in wave amplitude on a seismogram –or approximately a 32-fold increase in the energy released. Therefore a magnitude 6.7 earthquake releases over 900 times (32 times 32) the 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.