EARTH’S INTERIOR

EARTH’S DYNAMIC EARTH’S DYNAMIC SURFACESURFACE

CHARACTERIZED BY CONTINUOUS CHARACTERIZED BY CONTINUOUS CHANGECHANGE

EARTHQUAKES SEEM TO HAPPEN IN EARTHQUAKES SEEM TO HAPPEN IN SPECIFIC LOCATIONSSPECIFIC LOCATIONS

WHAT CAUSES THIS CONSTANTLY WHAT CAUSES THIS CONSTANTLY CHANGING SURFACE? CHANGING SURFACE?

TECTONIC PLATESTECTONIC 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 FAULTSEARTHQUAKES 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 FAULTTRANSFORM FAULTSAN ANDREAS FAULTSAN 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 WAVESSEISMIC WAVES

When earthquakes occur, waves of When earthquakes occur, waves of energy energy SEISMIC WAVESSEISMIC WAVES travel travel outward from the earthquake focus outward from the earthquake focus

3 types of seismic waves are 3 types of seismic waves are produced produced AT THE SAME TIMEAT THE SAME TIME but but each behaves differently within each behaves differently within earth.earth.

P WAVESP WAVES

Primary waves or compression waves Primary waves or compression waves vibrate parallel to the direction of vibrate parallel to the direction of movement. (slinky)movement. (slinky)

Travel faster than any other wave (6-Travel faster than any other wave (6-8 km./s)8 km./s)

Travel through solids, liquids, and Travel through solids, liquids, and gasesgases

S WAVES WAVE Shear wave or secondary waves Shear wave or secondary waves

vibrate back and forth perpendicular vibrate back and forth perpendicular to the direction the wave is movingto 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 ONLYTRAVEL THROUGH SOLIDS ONLY

SURFACE OR LONG WAVESSURFACE OR LONG WAVES Vibrations travel along earth’s Vibrations travel along earth’s

surface in a circular motion at surface in a circular motion at relatively slow speeds (2 kms/s) like relatively slow speeds (2 kms/s) like waves in a pondwaves in a pond

Do more Do more damage damage because they because they produce produce more ground more ground movementmovement

SEISMOGRAPH

SEISMOGRAM

VELOCITY OF SEISMIC VELOCITY OF SEISMIC WAVESWAVES

Velocity depends on the material Velocity depends on the material they are passing throughthey are passing through

a.a. Increase density and pressure – Increase density and pressure – greater the velocity greater the velocity

b.b.Waves are refracted or bent as Waves are refracted or bent as waves pass through material with waves pass through material with different densitiesdifferent densities

EARTHQUAKEEARTHQUAKE SHADOW SHADOW ZONESZONES

At an angle of 103° (distance 11,000 At an angle of 103° (distance 11,000 kms) from the epicenter both P and S kms) from the epicenter both P and S waves disappearwaves disappear

P waves can again be detected at P waves can again be detected at l42° (16,000 kms.) l42° (16,000 kms.)

NO S WAVES EVER APPEAR AGAINNO S WAVES EVER APPEAR AGAIN

THIS BAND OF 39° IN WHICH NO THIS BAND OF 39° IN WHICH NO WAVE ARE OBSERVED IS CALLED WAVE ARE OBSERVED IS CALLED THE THE EARTHQUAKE’S SHADOW ZONEEARTHQUAKE’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 LOCATING THE EPICENTER OF AN EARTHQUAKEAN EARTHQUAKE

The difference in travel time between P The difference in travel time between P and S waves can be used to determine the and S waves can be used to determine the DISTANCEDISTANCE from a station to the epicenter from a station to the epicenter

The farther a station is from the epicenter, The farther a station is from the epicenter, the GREATER the time interval between the GREATER the time interval between the arrival of P and S wavesthe arrival of P and S waves

TO DETERMINE THE EXACT LOCATION OF TO DETERMINE THE EXACT LOCATION OF AN EPICENTER, ITS DISTANCE FROM 3 AN EPICENTER, ITS DISTANCE FROM 3 STATIONS MUST BE DETERMINED AND 3 STATIONS MUST BE DETERMINED AND 3 CIRCLES DRAWNCIRCLES 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 LOCATING EARTHQUAKE EPICENTEREPICENTER

MUST HAVE DISTANCE FROM 3 SEISMOGRAPH STATIONS TO DETERMINE EPICENTER