copyright © by isiorho 1 earthquake slides modified from the original version by dr. s. a....
TRANSCRIPT
Copyright © by Isiorho 1
Earthquake Slides
Modified from the original version by Dr. S. A. Isiorho’s presentation
Copyright © by Isiorho 2
EarthquakesDefinitions Earthquake- the vibration of the ground due to the sudden
release of energy accumulated in a deformed rock Focus (Hypocenter)- spot underground where the rock
begins to break- point at which slip initiates Epicenter- the point on the land surface directly above the
focus Aftershock- tremors that occur as rocks adjust to their new
position Seismology- the study of earthquake
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Seismic WavesEarthquake’s energy is transmitted through the earth as seismic waves Two types of seismic waves radiate from the focus: Body waves- transmit energy through earth’s interior
Primary (P) wave- rocks vibrate parallel to direction of wave Compression and expansion (slinky example)
Secondary (S) wave- rocks move perpendicular to wave direction Rock shearing (rope-like or ‘wave’ in a stadium) S wave cannot travel through liquid Slower than P waves, but faster than surface waves
Surface waves- transmit energy along earth’s surface Love (L) wave- Rock moves from side to side like snake
Specific Body Waves:
Primary or “P” Primary or “P” WaveWave
Secondary or Secondary or “S” Wave“S” Wave
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Locating & Measuring Earthquake Seismometer- instruments that detect seismic waves Seismograph- device that measures the magnitude of
earthquake Seismogram is visual record of arrival time and magnitude of
shaking associated with seismic wave Mercalli Intensity scale
Measured by the amount of damage caused in human terms- I (low) to XII (high)
Richter Scale- (logarithmic scale) Magnitude- based on amplitude of the waves Earthquake total energy- uses moment magnitude scale
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Locating Epicenter & Focus Depth (EQ classification)
Use Arrival time at a recording station (time lag between P & S waves) to locate the epicenter of an earth quake Need three stations to determine the epicenter
Maximum Depth of Focus Shallow focus EQ < 70 km (45 mi) most earthquakes Intermediate focus EQ- 70-300 km (45- 180 mi) Deep focus EQ- > 300 km (> 180 mi)
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Richter Scale Richter scale is based on a log scale, meaning that each
subsequent number is ten times more in amplitude of vibration- this translates to about 30 times more energy than the previous number.
Example: an EQ of 5.0 is 10 times greater than an EQ of 4.0 on the Richter scale and is 30 times more in energy. An EQ of 5.0 is 100 times greater in amplitude than an EQ with 3.0 reading on the Richter scale
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Earthquake Locations
Most EQs occur in the circum pacific region80% of shallow focus EQ; 100% of deep focus EQ
Most EQs occur along plate boundariesOceanic trenches, Benioff zones, Mediterranean-
Himalayan Most EQs in US occur near the west coast
San-Andreas Fault
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Effects of Earthquakes Ground Displacement
Lateral and vertical
Landslides Liquefaction
Conversion of formally stable fine grain materials to a fluid mass
Seiches The back & forth movement of water in a semi-closed/closed body of water- could
cause flooding
Tsunamis- more from submarine landslide
Fire
Tsunami Movement: ~600 mph in deep waterTsunami Movement: ~600 mph in deep water ~250 mph in medium depth water ~250 mph in medium depth water ~35 mph in shallow water ~35 mph in shallow water
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