This piece is geared towards the general public, with an emphasis on Earth Science concepts for Middle-High School students. It could potentially be submitted for publication with a public science site such as ScienceNewsForKids.org.
Earthquakes happen regularly throughout the world, on a daily basis, but more people may be attuned to their presence this year, with 2011 including quakes rating high on the Richter scale as strong 5, 6, and 7’s in places such as Turkey, Chili, Greece, China, Pakistan, Japan, Argentina, Fiji, India, and even Virginia, Oklahoma, and Alaska in the United States. With events such as the incredible 9.0 quake off the coast of Japan in March – which triggered numerous intense aftershock quakes, and devastating historic levels of flooding and tsunamis – more people should be conscious Earth’s significant natural events.
While geologists are scientists who study what makes up the Earth and the processes which shape them, geophysicists are often mathematicians, physicists, and computer specialists working closely with geologists (2). When studying earthquakes or simply “quakes”, some of the many factors scientists consider are: the duration of, or amount of time that passes during, a quake; the types of rock the quake energy is having to pass through (rocks such as quartzite, granite, gabbro, albite, and novaculite); where it happens; the seismic intensity, or the quake’s strength; the slip rates; different pressures; friction; and heat.
These last variables, friction and heat, operate together in ways geophysicists are working to better understand. As blocks of the Earth’s crust move against or slide past each other, they create tremendous friction, which generates heat. With as fast as earthquakes can move solid rock – as fast as 1 meter per second! – it makes sense that tremendous amounts of heat are created by the friction the rock layers are causing as they move across one another. However, what geophysicists are finding is there might actually be less surface area creating or carrying the majority of the heat than they previously expected.
The research and experiments performed by Brown University geophysicists David Goldsby and Terry Tullis delves into the mechanics, or inner workings, of earthquakes, including how the movements of the crustal rocks which make up the Earth’s surface interact with each other. Breaks in the Earth’s crust which remain actively moving are called faults, making them different from things like canyons, gorges, or valleys. Specifically, the Goldsby and Tullis team have explored the uncertain mechanics and aspects of the sliding resistance of faults during earthquakes, and how we understand variables of pressure, friction, and the nuances of heat to interact.
Imagine two hands pressing flat against each other, with one hand pushing and sliding one way, while the other hand pushes and slides the opposite way, rubbing back and forth. If you rub the two hands across each other faster, you can feel them warm up as heat is generated from the friction created by the two surfaces of the hands meeting. The entire surface of each hand heats up. Previous thinking was that each side of the fault was moved against the other and friction was created across the entire surface area of each side of the fault, like the two separate hands coming together.
In actual earthquake events, research has shown that the heat generated by the seismic activity is not as consistent as at first thought. Goldsby and Tullis’ findings show that the heat generated by friction in faults during quakes can suddenly increase to an intense “flash” heat point around microscopic particles of rock, basically sand or dust. When flash heated, these particles move, reducing friction and allowing the surfaces of the fault they are between to move more easily, smoothly, and faster. Think of how some man-made machines use round ball-bearings to enable different parts to slide faster, or imagine again the two hands pressing together and sliding against each other; this time, however, add a fine granulated sand to the surface of the hands. Even adding something as small as sand particles between the two hand layers lets them slide more easily across each other.
How much heat is generated, at the points where the rock layers are actually in contact, can vary and depend on how much the sides of a fault move. This movement is known as the slip rate. If the slip rate is slow, the heat generated at the contact points has time to diffuse away, resulting in only a small rise in temperature (heat) and a negligible or unnoticeable effect on the strength of the other rock in that part of the fault. However, a high slip rate means there is not enough time for the heat created to diffuse away, or cool off. That point becomes both hot and weaker. This means that high contact stress, or pressure, and high slip speeds may create intense “flash heating” moments. The weakened areas of rock particles might even melt as the fault moves across them. It would be as if the sand between the hands, in the previous example, were the bits which got very hot and melted, while the rest of the surface of the hands were just warm.
These flash heated areas also may “heal” themselves faster – during or after a seismic event – than a normal crack, due to the rapid movement, melting, and then settling, because the frictional strength of an area recovers on a time scale shorter than that of a rupture or crack (4). Several different types of rock were compared during the course of the all of the research work, and the experiment results were similar. Uncertainties remain with the work, though, due to the difficulties of replicating the exact nature of earthquakes and all their factors in man-made laboratory settings.
“Uncertainty” is part of what makes scientists, like geophysicists and geologists, eager to keep studying the processes of the world we live in, and trying to find ways to explain and show how things actually work, and why and how they happen. Understanding natural processes allows people to make better choices interacting with different environments, such as where they might want to live, what to expect during an event naturally occurring in that area, how best to respond to an event, and what to do to prepare for it. Earthquake preparedness is possible with help and guidelines from such Internet websites as www.USGS.gov , the main page for information relating to the United States Geological Survey. There, you can learn more about earthquakes as they happen around the world, see maps and detailed data about quakes, and learn more about other Earth Science topics and how we, as people, relate to and are affected by all these incredible things.
Works Cited & Referenced During Essay Research
1. http://en.wikipedia.org/wiki/Geologist
2. http://www.seg.org/education/youth-resources/what-is-a-geophysicist
3. United States Geological Survey (USGS) website
a. Main page: http://www.usgs.gov/
b. Terminology : http://earthquake.usgs.gov/learn/glossary/?alpha=ALL
c. Significant Earthquakes of 2011 : http://earthquake.usgs.gov/earthquakes/eqarchives/significant/sig_2011.php
d. Goldsby and Tullis report, grant : http://earthquake.usgs.gov/research/external/research.php?award=&pi=®ionID=5&submit=Find+Projects&yearID=2008
4. David L. Goldsby, Terry E. Tullis, Flash Heating Leads to Low Frictional Strength of Crustal Rocks at Earthquake Slip Rates, in Science. 14 October 2011. http://www.sciencemag.org/content/334/6053/216.full
5. Earthquakes Generate Big Heat in Super-Small Areas, in ScienceDaily. 13 October 2011. http://www.sciencedaily.com/releases/2011/10/111013153947.htm
6. David L. Goldsby, Terry E. Tullis, Laboratory Experiments on Rock Friction Focused on Understanding Earthquake Mechanics. Report for grant # 08-HQGR0067. February 2009. https://docs.google.com/viewer?a=v&q=cache:1XuzKFmg24UJ:earthquake.usgs.gov/research/external/reports/08HQGR0067.pdf+&hl=en&gl=us&pid=bl&srcid=ADGEESh6Jchi2Pm9oa03-wc_Tk5A0MDUp-6CE-5mTo2TwkOfLEumhxh1t_u38zo1l-ozQgabMfriX70FTpUtQY5A6f-Wf9rAtsKzHobSmzBr_ZZBq1BBgA9T9lu0m28og72YxLeBjsZm&sig=AHIEtbRRmm_sLi7kQDaTHNn3ss82S3VUTg&pli=1
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