PowerPoint Presentation
Todays Schedule:HAZARD UPDATE!Review Lecture 3XXXXEarthquakes
(cont.)Stress and Strain (energy transfer)Elastic (bounces back)
vs. Plastic (stays deformed)Elastic Rebound TheoryTodays
MaterialEarthquakes (cont.)Stress and Strain (energy
transfer)Elastic (bounces back) vs. Plastic (stays deformed)Elastic
Rebound TheoryClass ReviewPreview Next Class
http://earthobservatory.nasa.gov/IOTD/view.php?id=84282&src=fb
Thoughphotographers,seismologists, andautomated webcamshave been
documenting the eruption near IcelandsBardarbungavolcano from the
ground, satellite imagery has been scarce because of persistent
cloud cover and a relatively small number of spacecraft that
collect images at high latitudes. But in the past few days, NASA
satellites have finally been able to observe the event from
orbit.At 12:45 p.m. Universal Time on August 31, 2014, theModerate
Resolution Imaging Spectroradiometer(MODIS) on NASAsAquasatellite
acquired these views of the eruption (above). The top, false-color
image uses a combination of infrared and visible light (MODISbands
7-2-1) to highlight the heat signatures of the erupting lava and to
distinguish glacial ice from clouds. In the lower, natural-color
image, the lava appears black.Overnight on September 1, the
Advanced Land Imager (ALI) on NASAsEarth Observing-1(EO-1)
satellite captured the first high-resolution view of the scene. The
image below is a composite of a natural-color observation from
August 27 overlaid with an infrared (IR) night view from September
1. The night view combines shortwave IR, near IR, and red
wavelengths (bands 9-7-5) to tease out the hottest areas within the
vent and lava field. The image shows at least a 1-kilometer fissure
and lava flowing in channels. The front of the flow has been moving
mostly to the northeast in recent days. (Download the large images
to see the day and night views separately.)Swarms of earthquakes
begannear the volcano on August 16, and tremors have persisted in
the weeks since (as many as 500 per day). To date, the Bardarbunga
eruption has produced lava flows and fountainssome reaching 200
meters, or 650 feetbut no large ash plumes. As of September 3,
theIcelandic Met Office reportedthat the new lava field spanned an
area of 7.2 square kilometers (2.8 square miles), slightly larger
than Gibraltar.Scientists are watching closely to see how molten
rock at and below the surface will interact with glacial ice,
surface melt, and groundwater; their concern is for flooding on or
near the Holuhraun lava field, or for steam explosions as water is
superheated by the magma. Icelandic researchers also have surmised
from GPS measurements of the deforming land surface that more magma
is entering the dyke than is erupting on the surface.References and
Related ReadingErik Klemettis Eruptions blog, viaWired(2014,
September 2)Bardarbunga.Accessed September 3, 2014.Icelandic Met
Office (2014)Brdarbungaupdated information.Accessed September
3,2014.NASA imagse by Jeff Schmaltz,LANCE/EOSDIS Rapid Responseand
Jesse Allen, using EO-1 ALI data provided courtesy ofthe NASA EO-1
team.Caption by Mike Carlowicz, with image interpretation from
Ashley Davies, NASA Jet Propulsion Laboratory.Instrument(s):EO-1 -
ALIAqua -
MODIS2http://earthobservatory.nasa.gov/IOTD/view.php?id=84282&src=fb
314 years ago (January 26, 1700), an estimated M9 earthquake
unzipped the Cascadia Subduction Zone fault from northern
California, USA to southern British Columbia, Canada, much like
recent events in 2011 in Japan and 2010 in Chile. The newly
released Cascadia Subduction Zone Earthquakes: A Magnitude 9.0
Earthquake Scenario examines how the Pacific Northwest may fare
after the next great megathrust earthquake and tsunami.
http://www.crew.org/sites/default/files/cascadia_subduction_scenario_2013.pdf
Turbidite Event HistoryMethods and Implications for Holocene
Paleoseismicity of the Cascadia Subduction
Zonehttp://pubs.usgs.gov/pp/pp1661f/
EarthquakeAnimation shows the buildup of stress along the margin
of two stuck plates that are trying to slide past one another. The
rock is deformed as it builds up strain in the plates; stress
increases along the contact.
http://www.youtube.com/watch?v=HQFTDAzhbZM&feature=player_embedded
http://www.iris.edu/hq/programs/education_and_outreach/animations/4What
is stress?Stress is defined as a force (F) acting on some area
(A).http://www.geology.sdsu.edu/visualstructure/vss/htm_hlp/stres_d.htm
http://serc.carleton.edu/quantskills/methods/quantlit/stressandstrain.htmlhttp://en.wikipedia.org/wiki/Stress_%28mechanics%29Stress
and Strain (Energy Transfer): What is stress and what is strain?
How do these relate to earthquakes?Additional resources:Stress:
Tension vs. Compression vs. ShearTensional stress is the stress
that tends to pull something apart. It is the stress component
perpendicular to a given surface, such as a fault plane, that
results from forces applied perpendicular to the surface or from
remote forces transmitted through the surrounding
rock.Compressional stress is stress that squeezes something. It is
the stress component perpendicular to a given surface, such as a
fault plane, that results from forces applied perpendicular to the
surface or from remote forces transmitted through the surrounding
rock.Shear stress is the stress component parallel to a given
surface, such as a fault plane, that results from forces applied
parallel to the surface or from remote forces transmitted through
the surrounding rock.
Image courtesy of Michael Kimberly, North Carolina State
Univ.http://earthquake.usgs.gov/learn/glossary/What is
strain?Strain is the relative change in shape or size of an object
due to externally-applied forces (e.g.
stress).http://physics.bgsu.edu/~stoner/p201/shm/sld002.htmHookes
Law: Stress is directly proportional to strain.
>>>>>>>>
http://en.wikipedia.org/wiki/Hooke%27s_lawWhat does elastic
mean?Elastic refers to internal strain in a material. This internal
strain is observed as a distortion of the material. Elastic
deformation returns to it's original shape after a strain is
applied.
http://en.wikipedia.org/wiki/Elastic_and_plastic_strainWhat does
plastic mean?Plastic refers to internal strain in a material. This
internal strain is observed as a distortion of the material.
Plastic deformation stays in the deformed shape after a strain is
applied.Earthquake MachineOn the graph, the yellow line shows the
movement of the hand over time, thus a steady line. The blue line
shows the movement of the block during slip on "earthquakes" thus
the jumps in distance over
time.http://www.iris.edu/hq/programs/education_and_outreach/animations/1
Activity 1
What is the Elastic Rebound Theory?The elastic rebound theory is
an explanation for how energy is spread during earthquakes. As
rocks on opposite sides of a fault are subjected to force and
shift, they accumulate energy and slowly deform until their
internal strength is exceeded. At that time, a sudden movement
occurs along the fault, releasing the accumulated energy, and the
rocks snap back to their original undeformed
shape.http://en.wikipedia.org/wiki/Elastic_rebound_theoryThe rocks
accumulate energy and slowly deform until their internal strength
is exceeded. At that time, a sudden movement occurs along the
fault, releasing the accumulated energy, and the rocks snap back to
their original undeformed shape.Reid's Elastic Rebound Theory
From an examination of the displacement of the ground surface
which accompanied the 1906 earthquake, Henry Fielding Reid,
Professor of Geology at Johns Hopkins University, concluded that
the earthquake must have involved an "elastic rebound" of
previously stored elastic stress.If a stretched rubber band is
broken or cut, elastic energy stored in the rubber band during the
stretching will suddenly be released. Similarly, the crust of the
earth can gradually store elastic stress that is released suddenly
during an earthquake.This gradual accumulation and release of
stress and strain is now referred to as the "elastic rebound
theory" of earthquakes. Most earthquakes are the result of the
sudden elastic rebound of previously stored energy.
http://earthquake.usgs.gov/regional/nca/1906/18april/reid.php
The following diagram illustrates the process. Start at the
bottom.
A straight fence is built across the San Andreas fault. As the
Pacific plate moves northwest, it gradually distorts the fence.
Just before an earthquake, the fence has an "S" shape. When the
earthquake occurs the distortion is released and the two parts of
the fence are again straight; but now there is an offset.
This diagram greatly exaggerates the distortion. Actually, the
distortion is spread over many miles and can only be seen with
precise instrumentation (e.g. GPS).
Review Lecture 4
Earthquakes: What are earthquakes? What causes them? What is the
results of an earthquake?Stress and Strain (Energy Transfer): What
is stress and what is strain? How do these relate to earthquakes?
What are the 3 different kinds of strain?Elastic Rebound Theory:
What is this and how does this relate to earthquakes?
One Minute Paper, that lasts three minutes.
I want to read about what you do understand. What is the most
exciting thing you learned today?
I want to read about what you do not understand. What may have
been confusing?
What is one question that you have about todays lecture?
We will cover these issues during our review of todays class at
the beginning of our next class.Next Class:
Origin of the EarthEarth StructurePlate Tectonics