EARTH’S INTERIOR

EARTH’S DYNAMIC SURFACE CHARACTERIZED BY CONTINUOUS CHANGE EARTHQUAKES SEEM TO HAPPEN IN SPECIFIC LOCATIONS 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

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

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.

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

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

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

SEISMOGRAPH SEISMOGRAM

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

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.

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 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

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 MUST HAVE DISTANCE FROM 3 SEISMOGRAPH STATIONS TO DETERMINE EPICENTER