Download Earthquakes

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