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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