Earthquake overview and Earthquake Engineering activity
Pattern of earthquakes defines the boundaries of tectonic platesThere are about 23 major plates
Three types of interactions between plates as they move around:Sliding past one another - transform boundaryRunning into one another - convergent boundaryMoving away from one another - divergent boundary
Where are earthquakes likely to occur? On faults? • Tectonic development of the New Madrid rift complex, Mississippi embayment, North America: • A rift was splitting apart the North American continent 600 million years ago • Rifting stopped • The continent has been under compression for at least 150 million years • The ancient faults may have been reactivated but are moving in the opposite sense by Lawrence W. Braile, William J. Hinze, G. Randy Keller, Edward G. Lidiak, and John L. Sexton; 1986; in Tectonophysics, Volume 131 (1986).
How strong will the ground shake? • http://quake.wr.usgs.gov/prepare/factsheets/NewMadrid • U.S. Geological Survey Fact Sheet-168-95 1995
What determines the level of shaking? • Magnitude • More energy released • Distance • Shaking decays with distance • Local soils • amplify the shaking
It is estimated that there are 500,000 detectable earthquakes in the world each year. 100,000 of those can be felt, and 100 of them cause damage. http://earthquake.usgs.gov/learning/facts.php
The magnitude of an earthquake is a measured value of the earthquake size. The magnitude is the same no matter where you are, or how strong or weak the shaking was in various locations. The intensity of an earthquake is a measure of the shaking created by the earthquake, and this value does vary with location. http://earthquake.usgs.gov/learning/facts.php
Richter magnitude scale • Because of the logarithmic basis of the scale, each whole number increase in magnitude represents a tenfold increase in measured amplitude; as an estimate of energy, each whole number step in the magnitude scale corresponds to the release of about 31 times more energy than the amount associated with the preceding whole number value.
Taken from: http://www.sdgs.usd.edu/publications/maps/earthquakes/rscale.htm
The 1906 San Francisco Earthquake (M~7.8) ~3 m right lateral offset on the San Andreas fault
The 1906 San Francisco Earthquake (M~7.8) San Francisco after the Earthquake and fire.
The 1906 San Francisco Earthquake (M~7.8) Comparison of fault lengths for selected significant events on the San Andreas.
Dec. 26, 2003 M6.6 Earthquake, Bam, Iran, ~80% of buildings destroyed
Earthquake Engineering Activity: • Supplies: (per group) • 1 sheet of card stock (cut into 1” wide 8 “ long strips) • 1 3x5 note card • 1 meter of tape • 1 tray • 1 golf ball • Ruler
Earthquake Engineering Activity: • Rules: • Must use only the materials provided • Structure must be 15 cm in height (the bottom of the ball must be 15 cm off the tray) • Structure must hold the golf ball (the ball cannot be taped down)