EARTHQUAKES
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
CONVERGING
Seafloor spreading
NORTH
SAN ANDREAS FAULT
PACIFIC PLATE
WEST SIDE MOVES
NORTH
EAST
WEST
NORTH AMERICAN
PLATE
EAST SIDE MOVES
SOUTH
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: 3:20
Missoula, Montana: 2:00
TAKE A PIECE OF PAPER, AND MARK
OFF THE DIFFERENCE IN ARRIVAL TIME
4:10
2800Km
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
2,800 km
Denver, Colorado: 3:20
2,000 km
Missoula, Montana 2:00
1,100 km
Recording Board
Difference in arrival times:
San Francisco: 41:0
2,800 km
5,000
4,000
3,000
2,000
0
1,000
Line your compass up to
the EXACT distance on the
scale. Use the metric side
(cm) beginning from zero.
.
.
.
Where do most of the earthquakes in the U.S. occur?
Tsunami (giant sea wave)
REMEMBER!
Emergency Preparedness Plan:
1. Duck and cover
2. Evacuation route and safe place to go to
3. Supply of clean water, food, blankets, flashlight, batteries, med.