EARTHQUAKES
SEISMOLOGY
- The study of earthquakes waves and how
they move through the body and around the
surface of the earth.
Seismic Waves vibrations generated in the earths interior that
carry energy away from the focus point of the
earthquake towards the surface of the earth
which is what we feel.
What are Earthquakes?
The shaking or trembling caused by the sudden
release of energy.
Usually associated with the faulting or breaking
of rocks along tectonic plates or faults (cracks in
the plates)
What is Elastic Rebound?
Energy is stored-up in rocks
Rock bend and stretch until the strength of the
rock is exceeded.
Rupture occurs and the rock quickly snap back
to the shape they were before the rupture
Energy WAVES are released and travel outward.
What is Elastic Rebound?
Prefix “Seis” - is from the Greek word “Seien”
which means “to shake”
Seismologist - a scientist who studies
earthquakes
Seismic Waves- waves of energy caused by the
sudden breaking/releasing of rock or an
explosion.
Seismograph/Seismometer - an instrument
used to record seismic activity
Seismogram - a record (paper or electronic)
produced by a seismograph.
Old School Seismograph
Seismogram Sample
Two main categories of seismic
waves:
1. Body Waves - travel through the Earth’s
interior only - two types of these:
A. Primary Waves (P Waves)
B. Secondary Waves (S Waves)
2. Surface Waves - travel along the Earth’s
surface only - also two types of these:
A. Love Waves (L Waves)
B. Rayleigh Waves ( R Waves)
Seismogram Sample
Body Waves
A. PRIMARY WAVES (P Waves):
Called Primary waves because they are the first
to arrive at a seismograph station.
the fastest of the seismic waves
can travel through solids or liquids
Seismogram Sample
Body Waves
A. PRIMARY WAVES (P Waves):
“Compressional”/push-and-pull wave action like
someone at the back of a line pushing and a
chain reaction results
The sound waves of thunder travel in the same
way...pushing and pulling on the air, shaking the
windows and walls of your house.
Body Waves - Secondary Waves
B. SECONDARY WAVES (S Waves):
Slower than P Waves
Can only move through solid rock, not liquids
Second Type- Surface Waves
A. LOVE WAVES (L Waves)
Fastest of the two types of surface waves
Cause the surface to move in a side-to-side
manner
Surface Waves - Rayleigh Waves
B.
RAYLEIGH WAVES (R Waves):
cause a “rolling” action across the surface
making the ground go up-and-down, and side to
side.
Most of the shaking felt during an earthquake is
caused by Rayleigh Waves.
Seismogram Example - Labeled
How are Earthquakes Measured?
The “size” of earthquakes is commonly
expressed in two ways: magnitude and
intensity.
The Richter Scale
Magnitude is a measure of the total energy
released during an earthquake. It is determined
from a seismogram, which plots the ground
motion produced by seismic waves. As devised
by C.F. Richter in 1935, the magnitude scale
allows us to compare earthquakes in relative
terms. It’s known as The Richter Scale.
The Richter Scale
The important thing to remember about
magnitude is that the scale is logarithmic, which
means that each step in magnitude represents a
TEN times increase in amplitude of wave
motion. Therefore, an earthquake of magnitude
6.0 has ten times the wave amplitude of an
earthquake of magnitude 5.0, a hundred times
the strength of a magnitude 4.0 earthquake, and
one thousand times the strength of a magnitude
3.0 earthquake.
The Richter Scale
What are the Epicenter and
Focus?
FOCUS - The point within the Earth where the
faulting begins, also known as the
HYPOCENTER
EPICENTER - The point directly above the
focus on the surface
How are the Focus & Epicenter
located?
These are located in much the same way a GPS
(global positioning system) knows where you are
and how fast you’re moving in a car. However,
instead of using satellites the way a GPS does,
seismologist use seismographs and seismic waves
to determine the focus & epicenter locations
through a process known as
TRIANGULATION.
Triangulation
In all honesty, the jobs of seismologist has been
made much simple with the invention of
networked, computerized sensors.
Instead of having to wait days or weeks for data
to be gathered from seismographs and then the
information be interpreted and calculations be
made, seismologist can get real-time results and
we can too at......
http://earthquake.usgs.gov
U.S. Geological Survey Earthquake Hazards
Program
This website has enough information and
incoming data to keep ANY seismologist busy.
The
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