Transcript Joe Murnane Earthquakes

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Earthquakes
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By Joe Murnane
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East
West
North
Earthquakes
Myths
Myths
• Mongolia, China
• A gigantic frog which
carried the world on
its back would twitch
periodically,
producing what we
now call earthquakes.
Myths
• Hindus of India
• The Hindus believed
that eight huge
elephants held up the
world. Whenever one
grew tired, it lowered
it’s head and shook ,
causing an
earthquake.
Myths
• Japan
• A giant catfish lived in mud
beneath the earth. The catfish
enjoyed playing pranks and
could only be held at bay by
Kashima,a god who protected
the Japanese. As long as
Kashima kept a mighty rock
with magical powers over the
catfish, the earth was still. But
whenever Kashima got lazy,
the catfish thrashed about,
causing earthquakes.
Myths
• Russia
• A god named Tuli
drove a sled filled with
the Earth. The sled
was pulled by dirty
dogs covered with
fleas. Whenever the
dogs stopped to
scratch, there was an
earthquake.
Myths
• Peru
• The Peruvian god would
periodically visit the earth
to count how many
people were there. When
he walked about, his
footsteps would caused
earthquakes. To shorten
his task, the people would
run out of their houses,
shouting such things as
"I'm here, I'm here!”
Earthquakes
Modern Myths
Modern Myths
• Many people believe because their home
is often shaken by small earthquakes that
they are protected from larger ones. Many
times the smaller quakes are actually
forerunners to larger earthquakes.
Modern Myths
• Many People believe that when an
earthquake happens, a chasm may open
up and anyone who falls in it will be lost in
the earth. Sudden movement along a fault
may create a shallow crevice but there has
never been any recordings of a person
falling into such a place and dying.
Modern Myths
• It has been speculated that in some way
Jupiter, Saturn, and Mars cause
earthquakes and that tidal movements
may also play a part. The most precise
scientific evaluations show no significant
relationship between earthquakes and
tidal loading.
Modern Myths
• Many people believe that earthquakes
cause volcanic eruptions. This is not true.
Earthquakes will occasionally happen in
the same area during, before, or after an
eruption, but are a result of the forces
which cause the eruption.
Modern Myths
• A theory was proposed that that
earthquakes happened in primarily
serene, cloudy conditions. They were
then proceeded by gale force winds,
meteors, and fireballs. This is not true.
Earthquakes are causes solely by geologic
processes and have no relation to weather
conditions.
Modern Myths
• At the present there is no known way to
prevent quakes. However, the amount of
destruction caused can be lessened but
quake resistant structures and proper
education.
Earthquakes
Cause
Cause
• Tectonics- processes, structures, and
landforms associated with deformation of
the Earth’s crust.
- Continents and ocean basins are largest
examples.
- Processes take place over hundreds of
millions (oceans), millions (mountain
ranges), hundreds of thousand (hills), and
in seconds (scarps).
• Tectonic Cycle- All the processes that
make up tectonics on a global scale
• Lithosphere- outer layer of Earth (crust
and upper mantle)
- Strong and rigid
- Broken into several pieces lithospheric
plates
- The plates move relative to eachother
Cause
• Asthenosphere- layer underlying
lithosphere made up flowing, hot, weak
rock.
- This layer is the cause for the movement
of the lithospheric plates.
- Causes continental movement
Cause
•
•
1.
2.
3.
The boundaries where lithospheric plates meet are
areas of great geological activity where earthquakes
are most common.
Three types of boundaries:
Divergent- occur where new lithosphere is made and
plates are moving away from each other.
Convergent- occur where one plate travels beneath
the edge of another plate “subduction.” (If both are
made of low-density material such as granite, a
continental-collision boundary can develop.) “Alps,
Himalayas”
Transform- occur where one or more plates slide past
one another, displacing ridges. “San Andreas Fault”
Cause
• Stress (force per unit area on a specified plane)
develops from these processes.
• Strain (deformation) increases as these
processes occur
• Elastic strain- deformation that is not permanent
• Elastic rebound- when elastic strain is released
• http://www.crustal.ucsb.edu/ics/understanding/el
astic/rebound.html
Cause
• When the stress caused by these processes
grows greater than the strength of the
surrounding rock, the rock ruptures, causing a
massive release of energy and seismic waves in
the form of an earthquake
• Because of this, this is why most earthquakes as
a rule occur on faults.
• Fault- a fracture or system of fractures where
rock has been displaced or deformed
Cause
• Intraplate earthquakes- earthquakes that
occur far from the plate boundaries
• Relatively rare
• Caused by weak portions of lithosphere
that break do to the stress caused by the
distant plate boundaries.
Cause
• Intensity
• Focus- the area where the rupture is
started and seismic energy first released.
• Epicenter- surface directly above the focus
• Deeper focus’ usually mean less damage
done to the epicenter.
Earthquakes
Detection
Detection
• Long-term
• Paleoseismology — Study of the
occurrence, size, and frequency of
historical earthquakes lacking instrumental
seismic records and prehistoric quakes.
• Two types of evidence:
Detection
• Geomorphic- deformed landform features
(fold scarps, fault scarps, uplifted coastal
terraces and deflected streams.)
• Stratigraphic- deformed sedimentary
deposits (lake, beach, subsidence, sand
boils, colluvial wedges, etc.)
Detection
• Common techniques
• Trenching- observation of faults to find the
“piercing point” (offset channel, pipe etc.)
• Seismic Reflection- shaking the ground via
explosions or electric vibrations to
measure vibration “waves.” Data is
compiled to make a model of possible
underground deformities caused by fault
offsets.
Detection
• Short-term
• Forecasting- specifies possible time period
and probability.
• Foreshocks- smaller earthquakes often
leading up to a single massive quake.
- Does not always occur
Detection
• Preseismic Uplift- Raising of earths crust
for a period of time before the earthquake
• Seismic Gaps- Areas along active fault
zones which are capable of producing
large quakes but have not in recent time.
Believed to store tectonic strain, thus
having good potential for future quake
sites.
Detection
• Electrical Resistivity- Before an
earthquake, rocks dilate and there is an
influx of water, decreasing electrical
resistivity.
• Radon increases from deep wells
• Animal Behavior
Detection
• Instruments
• Accelograph- Instrument used to measure
ground acceleration during seismic shaking
• Seismograph- Instrument used to measure
seismic waves
- Richter magnitude- determined by the largest
amplitude of seismic waves on a seismograph
- Modified Mercalli Scale
- http://www.seismo.unr.edu/ftp/pub/louie/class/10
0/mercalli.html
Detection
• From Space
• The ionosphere — an atmospheric region
filled with charged particles that blankets
the Earth between altitudes of about 75 to
1000 km.
• Fluctuations in the ionosphere=
ionospheric scintillations= signal delays in
GPS satellites
Detection
• From Space
• Ionosphere — works as a natural amplifier
of seismic waves moving across the
Earth's surface.
• Future use to detect seismic activity in
deep ocean or island areas.