9/19/2012 1 EARTHQUAKES Definition of Earthquake Ground trembling or shaking due to sudden release of energy accumulated in deformed rock. Rocks at relatively shallow depths in the Earth’s crust (cool and brittle) deform until they reach a yield point and break forming faults. At new ruptures or movement along older faults, strain energy is released suddenly and the earth quakes.
18
Embed
Definition of Earthquake - CCSF...9/19/2012 1 EARTHQUAKES Definition of Earthquake Ground trembling or shaking due to sudden release of energy accumulated in deformed rock. Rocks at
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
9/19/2012
1
EARTHQUAKES
Definition of Earthquake
Ground trembling or shaking due to sudden
release of energy accumulated in deformed
rock.
Rocks at relatively shallow depths in the Earth’s
crust (cool and brittle) deform until they reach a
yield point and break forming faults.
At new ruptures or movement along older faults,
strain energy is released suddenly and the earth
quakes.
9/19/2012
2
Aftershocks and Foreshocks
Aftershock — a series of smaller quakes that
occur after a major earthquake as the crust
readjusts to the change in stress.
Aftershocks are usually smaller but are very
destructive.
Foreshocks — small earthquakes that may (or
may not) precede a major quake by days to
years.
It is hoped that monitoring foreshocks may be
useful
as a prediction tool.
Location of an Earthquake
Focus (Hypocenter): precise underground location at
which rocks begin to rupture.
Epicenter: point on the Earth’s surface directly above
the focus.
The energy of an earthquake is
released from the slippage along a
fault and radiates in all directions.
9/19/2012
3
Seismology
Seismology is the study of earthquakes.
Seismographs are instruments that detect and record earthquakes.
In the seismograph, inertia tends to
keep the suspended mass motionless
while the recording surface (on a
rotating drum) vibrates with the
bedrock.
Thus the seismograph measures the
displacement or movement of the
ground as seismic waves pass through
the station.
QuickTime™ and a Cinepak decompressor are needed to see this picture.
Typical seismographs consist of
rotating drums with recording
paper.
Most modern seismographs
now record data digitally and
are available in near real time
on the internet.
USGS
9/19/2012
4
Some Uses of the Seismograph
Measurement of the energy released by an earthquake (Richter Magnitude)
Measurement of the location of an earthquake (epicenter)
Interpretation of the Interior of the Earth (Chapter 11)
Detection of underground nuclear bomb testing
Numerous spin-off apps
Thousands of seismographs are
deployed in national and international
networks to record earthquakes.
Seismographs
This extensive network
permits us to determine
the location of an
earthquake and to
study the earth’s
interior.
9/19/2012
5
Seismograms record the arrival of seismic energy at the recording
station.
Careful analysis of seismograms indicates that several different types
of seismic waves are recorded.
•Body waves travel through the
Earth’s interior and provide useful
information about the earthquake
and the interior structure of the
Earth.
•Surface waves move along the
surface of the Earth. They tend to be
the most destructive.
Seismic Waves – Seismic Energy Traveling
How does seismic energy propagate through the Earth?
earthquake
9/19/2012
6
Two types of body waves:
P-waves - primary waves -
compress and extend
material in the direction of
wave travel.
S-waves - secondary
waves move the material in
a direction that is normal to
the direction of wave travel.
Body Waves: P-waves
P-waves travel ~6 km/sec. They are
compressional waves and particle
motion is in the travel direction.
QuickTime™ and a Cinepak decompressor are needed to see this picture.
9/19/2012
7
Body Waves: S-waves
S-waves travel in the crust ~3.6 km/sec
(slower than p-waves). They
propagate through the Earth by
displacing particles perpendicular to
the direction of travel.
QuickTime™ and a Cinepak decompressor are needed to see this picture.
P-waves travel ~1.7 times
faster than s-waves.
Hence, the farther the
seismograph is from the
location of the earthquake
the greater the difference
in arrival times between
the p-wave and s-wave.
9/19/2012
8
Seismograms
From the arrival times of the different types of waves, we can see that