EARTHQUAKES
DEFINITION
Vibrations in the ground caused by a release of
energy along faults, (breaks), in the Earth’s
lithosphere as a result of plate tectonics.
MAIN CAUSES OF EARTHQUAKES
1. Plate movements
2. Volcanic Eruptions
3. Mining
4. Meteor Impacts
ROCK DEFORMATION
When a force is applied to a body of a rock at plate
boundaries, the rock may bend or break.
FAULTS
As stress builds in the deformed rock, a fault
can form.
Definition: Faults are a break in the Earth’s
lithosphere where one block of rock
moves toward, away from, or past
another.
TYPES OF FAULTS
1. Strike-slip
2. Normal
3. Reverse
STRIKE-SLIP
A strike-slip fault occurs when two blocks of rock slide
horizontally past each other in opposite directions.
Location: Transform Plate Boundaries
STRIKE-SLIP FAULT
NORMAL FAULT
Tectonic forces pull two blocks of rock apart. The block of
rock above the fault moves down relative to the block of rock
below the fault.
Location: Divergent Plate Boundary
NORMAL FAULT
REVERSE FAULT
Tectonic forces push two blocks of rock together.
The block of rock above the fault moves up relative to
the block below the fault.
Location: Convergent Plate Boundaries.
REVERSE FAULT
FOCUS & EPICENTER
Focus: The location inside the Earth where the
rock first begins to move or break.
Epicenter: The location on the earth’s surface
which is directly above the focus.
FOCUS & EPICENTER
SEISMIC (BODY) WAVES
When rocks move along a fault, a release of
energy travels out in all directions as waves from
the focus.
TYPES OF SEISMIC WAVES
1. Primary Waves: P-waves
2. Secondary Waves: S-waves
3. Surface Waves
PRIMARY WAVES
P-waves cause rock in the ground to move in a push-pull
motion similar to spring. P-waves are the fastest moving of
all seismic waves.
SECONDARY (SHEAR) WAVES
S-waves cause the rocks to move up and down at
right angles relative to the direction the wave is
traveling.
SURFACE WAVES
Surface waves travel along the Earth’s surface
moving rocks up and down in a rolling motion.
Surface waves are the slowest type of seismic
waves.
TYPES OF SURFACE WAVES
1. Love Waves
2. Rayleigh Waves
LOVE WAVES
Love waves causes the rock to move side to side in a
directions perpendicular to the waves’ direction of travel.
RAYLEIGH WAVES
Rayleigh waves are slow moving waves that travel along
the surface in a rolling motion similar to ocean waves.
LOCATING THE EPICENTER
An instrument called a seismometer measures and
records ground motion and can be used to determine the
distance seismic waves have traveled.
SEISMOMETER
SEISMOGRAM
ANALYZING THE DATA
Step 1:
Determine the number of seconds between the
arrival time of the first P-wave and the first Swave. This time difference is know as
“Lag Time”. The lag time must be calculated from
at least 3 different recording stations.
ANALYZING THE DATA CONTINUED
Step 2: Plot the lag times found from the three recording
stations on a (S-P) Lag Time Graph in order to
determine the distance to the epicenter.
ANALYZING THE DATA CONTINUED
Step 3: Using a ruler and a map scale to measure the
distance between the seismometer and the
earthquakes epicenter.
Step 4: Place the point of a compass on the seismometer
location and the pencil on the distance away from
the epicenter. Next, draw a circle around the
seismometer. Repeat this step for the other two
recording stations.
THE EPICENTER
Where the three triangulated circles intersect is the
location of the epicenter of the earthquake.
DETERMINING AN EARTHQUAKES MAGNITUDE
Scientists use three different scales to measure and
describe an earthquakes magnitude. Magnitude is a
measure of the amount of energy released during an
earthquake.
1. Richter Magnitude Scale
2. Moment Magnitude Scale
3. Modified Mercalli Scale
RICHTER SCALE
The Richter scale is used to interpret two different values
recorded by the seismometer.
1. The amount of ground motion.
2. The amount of energy released by the earthquake
GROUND MOTION
The Richter scale begins at zero but has no upper limits.
Each increase of 1 unit represents ten times the amount
of ground motion.
Example: A magnitude 8 produces ten times greater
ground shaking than a magnitude 7.
The ground motion value is the measure used to alert the
general public.
ENERGY RELEASE
The Richter scale also measures the energy released by
the earthquake. On this scale each increase of one whole
number, is represented by a 31-fold increase in energy.
Example: A magnitude 8 is 31 times more powerful than a
magnitude 7
MOMENT MAGNITUDE SCALE
The moment magnitude scale measures the total amount
of energy released by an earthquake. The energy
released depends on three factors:
1. The size of the fault
2. The amount of motion that occurs along the fault
3. The strength of the rocks that break during the
earthquake.
MOMENT MAGNITUDE SCALE CONTINUED
On this scale for each increase of one unit the earthquake
releases 31.5 times more energy.
Example: A magnitude 8 earthquake releases more than
992 times more energy than a magnitude 6.
MODIFIED MERCALLI SCALE
On the Modified Mercalli scale, an earthquakes magnitude
is measured by the amount of damage caused by ground
motion. This scale ranges from 1 – 12. 1 being minimal
and 12 being total destruction.
LARGEST RECORDED EARTHQUAKE
The largest ever recorded earthquake occurred in Chile.
May 22nd 1960 at 11:19:14 UTC a magnitude 9.5
earthquake was recorded. Approximately 1,655 killed,
3,000 injured, 2,000,000 homeless, and $550 million
damage in southern Chile; tsunami caused 61 deaths,
$75 million damage in Hawaii; 138 deaths and $50 million
damage in Japan; 32 dead and missing in the Philippines;
and $500,000 damage to the west coast of the United
States.
ASSOCIATED EARTHQUAKE HAZARDS
1. Aftershocks
2. Fires
3. Tsunamis
4. Liquefaction
LIQUEFACTION
Liquefaction occurs when loose soil temporarily takes on
some properties of a liquid. (Quicksand)
RESULTS OF LIQUEFACTION
HOW CAN EARTHQUAKES BE USED
Seismologists have used earthquakes to map the Earth’s
interior. P and S waves change speed and direction
depending on the density of different materials. Scientists
have found that S-waves cannot travel through the outer
core, proving it is liquid. By studying the P-waves
scientists were also able to determine that the inner core
is composed of iron and nickel.
EARTH’S INTERIOR USING SEISMOLOGY