EARTH’S INTERIOR

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

TECTONIC PLATES EARTHQUAKES HAPPEN AT TECTONIC PLATE BOUNDARIES

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

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

NORMAL FAULT REVERSE FAULT TRANSFORM FAULT

TRANSFORM FAULT SAN ANDREAS FAULT FREQUENT EARTHQUAKES

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

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

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

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

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 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

SEISMOGRAPH SEISMOGRAM

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

EARTHQUAKE SHADOW ZONES At an angle of 103° (distance 11,000 kms) from the epicenter both P and S waves disappear 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.) P waves can again be detected at l42° (16,000 kms.) NO S WAVES EVER APPEAR AGAIN NO S WAVES EVER APPEAR AGAIN THIS BAND OF 39° IN WHICH NO WAVE ARE OBSERVED IS CALLED THE EARTHQUAKE’S SHADOW ZONE THIS BAND OF 39° IN WHICH NO WAVE ARE OBSERVED IS CALLED THE EARTHQUAKE’S SHADOW ZONE

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

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

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 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 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 TO DETERMINE THE EXACT LOCATION OF AN EPICENTER, ITS DISTANCE FROM 3 STATIONS MUST BE DETERMINED AND 3 CIRCLES DRAWN

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

LOCATING EARTHQUAKE EPICENTER LOCATING EARTHQUAKE EPICENTER MUST HAVE DISTANCE FROM 3 SEISMOGRAPH STATIONS TO DETERMINE EPICENTER