FORCES INSIDE EARTH Objectives
Explain how earthquakes result from the buildup of stress in Earth’s crust
Contrast normal, reverse, and strike-slip faults
CAUSES OF EARTHQUAKES Passing the Elastic Limit Causes
FaultingApplied stresses can cause rocks to bend
and stretch Eventually rocks will break away from one
anotherArea in which the rocks break and
move is called a faultVibrations produced is called an
earthquakeEarth’s crust movement causes the stresses
applied
TENSION The rocks on the crust are being
stretched as two plates are moving apart
The middle becomes thinner until a normal fault occurs
TYPES OF FAULTS P.120 Normal Fault
Earth’s plates move apart
Movement of the plates causes tension
Rocks above the fault surface move downward in relation to the rocks below the fault surface
COMPRESSION This stress force squeezes rock until it
folds or breaks This can create a reverse fault
TYPES OF FAULTS P.121 Reverse Faults
Compression forces are applied because Earth’s plates are coming together
Causes rocks to bend and break
Rocks above the fault surface are forced up and over the rocks below the fault surface
SHEARING This stress force pushes rock in two
opposite directions This can cause a strike-slip fault
TYPES OF FAULTS P.121 Strike-slip Fault
Earth’s plates move sideways to one another
Creates a shear force
Rocks on either side of the fault surface are moving past each other without much upward or downward movement
EARTHQUAKE INFORMATION Objectives
Compare and contrast primary, secondary, and surface waves
Explain how an earthquake epicenter is located using seismic wave information
Describe how seismic wave studies indicate the structure of Earth’s interior
TYPES OF SEISMIC WAVES P.125 Earthquake focus
Focus – the point in Earth’s interior where the energy waves are produced
Seismic wavesSeismic wave - the energy waves that move
outward from the earthquake focus and make the ground quake
EpicenterThe point on Earth’s surface directly above
the earthquake focus
TYPES OF SEISMIC WAVES P.127 Seismic Waves
Primary wavesEnergy waves that cause rocks to
move back and forth in the same direction
Compression and stretching forces are created
Secondary wavesEnergy waves that cause rocks to
move at right angles to the wave
TYPES OF SEISMIC WAVESSurface waves
Energy waves that reach the Earth’s surface
Energy waves that move rocks in an elliptical motion
LOCATING AN EPICENTER P.130 Seismic waves do not travel through
earth’s surface at the same speedPrimary waves are the fastestSurface waves are the slowest
Seismograph stationsRecord the information from the earthquake
by recording the different types of waves as they reach the station
LOCATING AND EPICENTER P.131 Epicenter Location
If information is received from the earthquake at three stations, then the epicenter can be located
A circle is drawn around each station on a mapThe radius is equal to the distance
from the station to the epicenterThe point in which all three circles intersect
is the earthquake epicenter
USING SEISMIC WAVES TO MAP EARTH’S INTERIOR The speed of the waves changes as the
depth changesThe speed changes in accordance to the
density of the layers of Earth
USING SEISMIC WAVES TO MAP EARTH’S INTERIOR Structure of Earth
Inner coreSolid and very denseComposed of mostly nickel and
ironOuter core
Liquid layer that surrounds the inner core
Composed of nickel and iron
USING SEISMIC WAVES TO MAP EARTH’S INTERIOR
MantleLargest layer located above the
inner coreComposed of silicon, oxygen,
magnesium, and ironCrust
Outermost layerSolid and similar in composition to
the mantle
USING SEISMIC WAVES TO MAP EARTH’S INTERIOR Moho Discontinuity
Boundary between the crust and the mantleSeismic waves speed up as they reach this
area Seismic waves speed up as they
reach more dense areas and slow down when the reach less dense areasThe more solid the layer the more dense
USING SEISMIC WAVES TO MAP EARTH’S INTERIOR Shadow zone
The area between 105-140 degrees from the epicenter
Area in which seismic waves can’t be detected
What is the cause?Secondary waves can’t be
transmitted through liquid layersPrimary waves are slowed and
deflected by the outer core and speed up again when the reach the solid inner core
DESTRUCTION BY EARTHQUAKES Objectives
Define magnitude and Richter scaleList ways to make your classroom and home
more earthquake safe
MEASURING EARTHQUAKES P. 135 Seismology
Seismologists - People who study earthquakes and seismic waves
Use instruments called seismographsRecord seismic wavesA drum with a sheet of paper
vibrates and a stationary pen marks the vibrations on the paper
The height of the lines are used to measure the energy released from the earthquake called the magnitude
MEASURING EARTHQUAKES P.128 Earthquake Magnitude
Usually determines the strength of the break
Doesn’t determine the duration or the sizeFor each increase of 1is 10 times stronger
An earthquake of 4 is 10 times stronger than an earthquake of 3
TSUNAMIS P.137 Caused by the movement of the
ocean floorCauses a disruption in the waterSome are so wide that a large ship can
travel over the wave without knowingRecent earthquake in the Indian Ocean
created a tsunamis that was 100 feet high and moving at 500 mph
EARTHQUAKE SAFETY Quake proofing your home
Place heavy objects near the floorFix gas appliances in place
9.4 LIVING ON A FAULT Objectives
Recognize that most loss of life in an earthquake is caused by the destruction of human-made structures
Consider who should pay for making structures seismic safe
WHO SHOULD PAY FOR EARTHQUAKE PREPARATION? Seismic safe structures
Structures that are resistant to the vibrations of Earth’s crust
Structures are made with mooringsMade of steel and are filled with
alternating layers of rubber and steel
These structures absorb the energy produced from the earthquake