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EARTHQUAKESEARTHQUAKES
WHAT YOU NEED TO KNOW!
TECTONIC PLATES
EARTHQUAKES HAPPEN AT TECTONIC PLATE BOUNDARIES
ANALYSIS OF SEISMIC WAVES
HAVE RESULTED IN
THE INFERENCE ABOUT EARTH’S
INTERIOR
S WAVES CANNOT PASS THROUGH THE LIQUID OUTER
CORE
EARTHQUAKE SHADOW
ZONES
NO WAVES OCCUR BETWEEN 105º -140º
S WAVES DISAPPEAR FROM 105º NEVER TO APPEAR AGAIN
CONVECTION CURRENTS IN THE ASTHENOSPHERE CAUSE THE PLATES TO MOVE IN DIFFERENT DIRECTIONS – LOOK AT ARROWS
DIVERGING DIVERGING
CONVERGINGCONVERGING
Seafloor spreading
NORTH
WEST
SOUTH
EAST
SAN ANDREAS FAULT
PACIFIC PLATE
WEST SIDE MOVES NORTH
NORTH AMERICAN PLATE
EAST SIDE MOVES SOUTH
P WAVES
• Primary waves (compression waves) vibrate parallel to the direction of movement. (push-pull like a slinky)
• Travel faster than any other wave (6-8 km./s)
• Travel through solids, liquids, and gases
S WAVE
• Secondary wave (shear waves) vibrate side to side to the direction the wave is moving
• Slower than P waves (4-5 kms./s)
• TRAVEL THROUGH SOLIDS ONLY
Finding an Earthquake
Epicenter
What is an Epicenter?• A point on the surface of the Earth directly
above the FOCUS of the earthquake.
•The point within the Earth from which earthquake waves originate.
Use the data from the recording stations:
• Station A: San Francisco, California
P-Wave arrival 3:02:20 S-Wave arrival 3:06:30
What is the time difference between P and S wave arrivals?
Use the data from the recording stations:
• Station B: Denver, Colorado
P-Wave arrival 3:01:40 S-Wave arrival 3:05:00
What is the time difference between P and S wave arrivals?
Use the data from the recording stations:
• Station C: Missoula, Montana
P-Wave arrival 3:01:00 S-Wave arrival 3:03:00
What is the time difference between P and S wave arrivals?
Difference in arrival times:
San Francisco: 4:10
Denver, Colorado: 3:20Missoula, Montana: 2:00
TAKE A PIECE OF PAPER, AND MARK OFF THE DIFFERENCE IN ARRIVAL TIME
2800Km
4:10
MOVE THE PAPER UNTIL THE TWO TICK MARKS LINE UP WITH THE P AND S CURVES
WHEN TICK MARKS LINE UP, GO STRAIGHT DOWN AND READ THE EPICENTER DISTANCE
EPICENTER DISTANCE OF 2800 KM
EPICENTER DISTANCES
San Francisco: 4:10
Denver, Colorado: 3:20Missoula, Montana 2:00
2,800 km
1,100 km
2,000 km
Recording BoardDifference in arrival times:
San Francisco: 41:02,800 km
1,00
0
2,00
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3,00
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4,00
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5,00
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Line your compass up to the EXACT distance on the scale. Use the metric side (cm) beginning from zero.
0
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Where do most of the earthquakes in the U.S. occur?Where do most of the earthquakes in the U.S. occur?
Tsunami (giant sea wave)
REMEMBER!REMEMBER!
Emergency Preparedness Plan:Emergency Preparedness Plan:1.Duck and cover2.Evacuation route and safe place to go to3.Supply of clean water, food, blankets, flashlight, batteries, med.
