1. EARTH’S INTERIOR

3. EARTH’S DYNAMIC SURFACE
CHARACTERIZED BY CONTINUOUS CHANGE
EARTHQUAKES SEEM TO HAPPEN IN SPECIFIC LOCATIONS
WHAT CAUSES THIS CONSTANTLY CHANGING SURFACE?

5. TECTONIC PLATES
EARTHQUAKES HAPPEN AT TECTONIC PLATE BOUNDARIES

7. CONVECTION CURRENTS IN THE ASTHENOSPHERE CAUSE THE PLATES TO MOVE IN DIFFERENT DIRECTIONS – LOOK AT ARROWS
DIVERGING
CONVERGING

8. EARTHQUAKES AND FAULTS
An earthquake is caused by the sudden release of energy stored in rocks along a fault
Fault is a crack in a mass of rock along which there has been movement of rock layers on either side of the crack
Focus – where EQ starts below surface
Epicenter – location directly above on land or water

10. NORMAL FAULT
REVERSE FAULT
TRANSFORM FAULT

11. TRANSFORM FAULT SAN ANDREAS FAULT
FREQUENT EARTHQUAKES

12. SAN ANDREAS FAULT PACIFIC PLATE WEST SIDE MOVES NORTH
NORTH AMERICAN PLATE
EAST SIDE MOVES SOUTH
EAST
WEST
SOUTH

15. SEISMIC WAVES
When earthquakes occur, waves of energy SEISMIC WAVES travel outward from the earthquake focus
3 types of seismic waves are produced AT THE SAME TIME but each behaves differently within earth.

16. P WAVES
Primary waves or compression waves vibrate parallel to the direction of movement. (slinky)
Travel faster than any other wave (6-8 km./s)
Travel through solids, liquids, and gases

17. S WAVE
Shear wave or secondary waves vibrate back and forth perpendicular to the direction the wave is moving
Slower than P waves (4-5 kms./s)
TRAVEL THROUGH SOLIDS ONLY

18. SURFACE OR LONG WAVES
Vibrations travel along earth’s surface in a circular motion at relatively slow speeds (2 kms/s) like waves in a pond
Do more damage
because they produce
more ground movement

23. SEISMOGRAPH
SEISMOGRAM

24. VELOCITY OF SEISMIC WAVES
Velocity depends on the material they are passing through
Increase density and pressure – greater the velocity
Waves are refracted or bent as waves pass through material with different densities

25. EARTHQUAKE SHADOW ZONES
At an angle of 103° (distance 11,000 kms) from the epicenter both P and S waves disappear
P waves can again be detected at l42° (16,000 kms.)
NO S WAVES EVER APPEAR AGAIN
THIS BAND OF 39° IN WHICH NO WAVE ARE OBSERVED IS CALLED THE EARTHQUAKE’S SHADOW ZONE
However, scientists noticed something unusual. When the angle around the earth’s circumference from the epicenter is more than 102 (This is a distance of about 11,000 kms.) both the P and S waves disappear. Then the P waves can again be detected if the station is more than l43 (l6,000 kms.). NO S WAVE ARE EVER OBSERVED. THE RESULT IS A BAND OF ABOUT 41 OR 4500 KMS. wide in which no waves are observed. This region is called the earthquake’s shadow zone. Location of the shadow zone will depend on the focus of the EQ. Each EQ produces its own shadow zone.

26. EARTHQUAKE SHADOW ZONES
P WAVES DISAPPEAR FROM º -140º
S WAVES DISAPPEAR FROM 105º NEVER TO APPEAR AGAIN

27. ANALYSIS OF SEISMIC WAVES HAVE RESULTED IN THE INFERENCE ABOUT EARTH’S INTERIOR
S WAVES CANNOT PASS THROUGH THE LIQUID OUTER CORE

28. LOCATING THE EPICENTER OF AN EARTHQUAKE
The difference in travel time between P and S waves can be used to determine the DISTANCE from a station to the epicenter
The farther a station is from the epicenter, the GREATER the time interval between the arrival of P and S waves
TO DETERMINE THE EXACT LOCATION OF AN EPICENTER, ITS DISTANCE FROM 3 STATIONS MUST BE DETERMINED AND 3 CIRCLES DRAWN

29. P WAVES TRAVEL FASTER THAN S WAVES
AS DISTANCE FROM EPICENTER INCREASES -THE GREATER THE TIME INTERVAL BETWEEN P AND S WAVES

31. LOCATING EARTHQUAKE EPICENTER
MUST HAVE DISTANCE FROM SEISMOGRAPH STATIONS TO DETERMINE EPICENTER