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What are earthquakes?. Earthquakes occur mainly at plate boundaries. http://vulcan.wr.usgs.gov/Imgs/Gif/PlateTectonics/Maps/map_quakes_volcanoes_plates.gif. Pressure. Pressure builds up as plates move. Eventually rocks break at a fault . Energy is released as seismic waves . (3 kinds). - PowerPoint PPT Presentation
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What are earthquakes?
• Earthquakes occur mainly at plate boundariesplate boundaries.
http://vulcan.wr.usgs.gov/Imgs/Gif/PlateTectonics/Maps/map_quakes_volcanoes_plates.gif
Pressure
• Pressure builds up as plates move.
• Eventually rocks break at a faultfault.
• Energy is released as seismic seismic waveswaves. (3 kinds)
Types of Forces and Faults
Normal Faults
Tension – pulling rocks apart
Reverse Faults
Compression– pushing rocks together
Strike-Slip Faults
• Caused by shearing
Describing the location
Earthquakes occur underground. The spot underground where the rock breaks
is the focusfocus. The spot on the surface directly above that is
the epicenterepicenter.
http://www.harcourtschool.com/scienceglossary/images/gr4/epicenter4.jpg
Types of Waves
Primary WavesPrimary Waves (first) – longitudinal waves that travel the fastest- originate at the focus
These are the first sign of an earthquake
http://astro.uchicago.edu/cara/outreach/se/ysi/1999/intro2.html
Secondary Waves
Transverse Waves that start out at the focus
http://astro.uchicago.edu/cara/outreach/se/ysi/1999/intro2.html
Surface Waves
Originate at the epicenter (on the surface)
Cause the most destruction
http://www.gly.fsu.edu/~salters/GLY1000/Chapter4/Slide18.jpg
How far away?
• The lag time between the primary and secondary waves is used to determine how far away the earthquake occurred
Measuring an Earthquake
SeismometersSeismometers – instruments used to sense and record earthquake data
http://www.thetech.org/exhibits/online/quakes/seismo/
Measuring an Earthquake
SeismographsSeismographs – recordings of seismic waves produced by seismometers
http://www.thetech.org/exhibits/online/quakes/seismo/
http://www.inel.gov/env-energyscience/seismic/network.shtml
Amplitude
• The height of a wave
Locating the epicenter
3 Seismograph stations are required to triangulate the location
http://www.tecedu.com/about/images/us-map.gif
Richter ScaleMeasures the magnitude of earthquakes
using the distance from the epicenter and the amplitude of the largest wave.
http://www.wanadoo.jo/medias/img/SGE.GXY52.050904182653.photo00.default-245x208.jpg
Determining Richter scale
Richter ScaleEach number increase on the Richter
scale indicates an increase of
10x’s in amplitude
32 x’s more energy
http://www.wanadoo.jo/medias/img/SGE.GXY52.050904182653.photo00.default-245x208.jpg
Historic Earthquakes
Alaska 1964, 9.2
http://epod.usra.edu/archive/images/augustanack3.jpghttp://earth.geol.ksu.edu/sgao/g100/plots/1031_earthquake_trig.jpg
http://www.tfhrc.gov/pubrds/03nov/images/mccarthy2.jpg
http://www.tfhrc.gov/pubrds/03nov/05.htmhttp://www.disasterrelief.org/Disasters/010326alaskaquake1964/Images/rail.gif
Modified Mercalli Scale
Measures intensity or damage caused by an earthquake
I -XII
http://elearning.niu.edu/simulations/images/S_portfolio/Mercalli/Mercalli_Scale.swf
Moment magnitude scale
Used to record energy released by an earthquake and takes into account the size of the fault rupture.
Tsunamis
• are large fast moving waves that are produced by moving crust under the ocean
Recent Tsunami’s
