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Earthquakes GLG 101 - Physical Geology Bob Leighty These notes and web links are your primary “lecture” content in this class. Additionally, various articles are assigned each week to supplement this “lecture” information. I believe you’ll have enough information to reference without having to purchase a costly textbook. These lecture notes are very similar to the ones I use in my traditional classes. You’ll find they are loaded with imagery and streamlined text that highlight the most essential terms and concepts. The notes provide a framework for learning and, by themselves, are not meant to be a comprehensive source of information. To take advantage of the global knowledge base known as the Internet, I have included numerous hyperlinks to external web sites (like the Wikipedia, USGS, NASA, etc.). Follow the links and scan them for relevant info. The information from linked web sites is meant to supplement and reinforce the lecture notes – you won’t be responsible for knowing everything contained in them. As a distance learning student, you need to explore and understand the content more independently than in a traditional class. As always, I will help guide you through this learning adventure. Remember, email Dr. Bob if you have any questions about today’s lecture ([email protected]). Leave no questions behind! Explore and have fun! Earthquakes What’s Shakin’? National Earthquake Information Center (NEIC) World seismicity 1990-2000 Earthquakes Earthquakes: why do we care? Destructive (in lives & property) Mexico City (1985) Earthquakes Earthquakes: why do we care? Some types of building sites are better than others > Bedrock is better than soft sediment Earthquakes Earthquakes: why do we care? We can learn about the Earth's interior & tectonic plates Earthquakes What is an earthquake? Elastic rebound theory - Stress builds up until rocks deform elastically and then break, releasing energy Quake = A sudden release of stored energy causing vibrations (seismic waves) in rock The size of a quake the amount of built-up stress Earthquakes Where do earthquakes occur? Originate within the brittle part of the lithosphere Mostly occur at plate boundaries (~95%) Earthquakes Where do earthquakes occur? Focus - The actual location within the Earth where the earthquake originates Epicenter - The point on the Earth's surface above the focus Earthquakes Seismic Waves Body Waves P-waves P-wave = primary wave or compressional wave Fastest (4 to 7 km/sec) Can move through solids & liquids Earthquakes Seismic Waves Body Waves S-waves S-wave = secondary wave or shear wave Slower (2 to 5 km/sec) Can move only through solids Earthquakes Locating Earthquakes Seismometer - Detects and records vibrations (earthquakes, nuclear blasts, etc.) Earthquakes Locating Earthquakes Seismogram - Record of vibrations (paper, electronic) Earthquakes Locating Earthquakes surface P lag time S Earthquakes Locating Earthquakes To get the distance to an earthquake epicenter, we need: 1) the difference in arrival times (lag time) between P & S waves 2) data from 3 different seismic stations Earthquakes Earthquake Intensity Magnitude Richter Scale = measures earthquake intensity (energy) from ground shaking Determined by measuring amplitude (height) of the S-wave on seismogram Richter scale is logarithmic (each interval x10) Seismic Moment Scale - A better estimate of earthquake energy, now the standard Earthquakes Controls on Earthquake Damage Distance from focus / depth of earthquake Soft sediment vs. dense bedrock Duration of earthquake Population density Building design and construction Earthquakes Destructive Effects Ground Rupture Earthquakes Destructive Effects Ground Rupture Earthquakes Destructive Effects Liquefaction Liquifaction - Soft sediment can amplify vibrations (watersaturated sediment can liquefy & turn to goop) Earthquakes Destructive Effects Fire Broken gas lines, water pipes, etc. ex - San Francisco, CA (1906): 90% of EQ damage caused by fire ex - Yokohama, Japan (1923): 576,262 houses burned, 143,000 people killed Earthquakes Destructive Effects Tsunami Tsunami - Caused by the sudden displacement of water NOT a tidal wave Earthquakes Destructive Effects Tsunami Fast, but low in open ocean Big & bad near shore (average up to 30 m high) Earthquakes Destructive Effects Tsunami Earthquakes Destructive Effects Tsunami http://www.ess.washington.edu/tsunami/index.html http://www.volcanolive.com/tsunami10.html http://serc.carleton.edu/NAGTWorkshops/visualization/collections/tsunami.html Earthquakes Destructive Effects Tsunami Earthquakes WWW Links in this Lecture > NEIC - http://earthquake.usgs.gov/regional/neic/ > Tectonic plates - http://en.wikipedia.org/wiki/Tectonic_plates > Elastic Rebound Theory - http://en.wikipedia.org/wiki/Elastic_rebound_theory > Earthquake - http://en.wikipedia.org/wiki/Earthquake > Lithosphere - http://en.wikipedia.org/wiki/Lithosphere > Epicenter - http://en.wikipedia.org/wiki/Epicenter > Seismic waves - http://en.wikipedia.org/wiki/Seismic_wave > P-wave - http://en.wikipedia.org/wiki/P_wave > S-wave - http://en.wikipedia.org/wiki/S_wave > Seismometer - http://en.wikipedia.org/wiki/Seismometer > Seismogram - http://en.wikipedia.org/wiki/Seismogram > Richter Scale - http://en.wikipedia.org/wiki/Richter_magnitude_scale > Liquifaction - http://en.wikipedia.org/wiki/Earthquake_liquefaction > Tsunami - http://en.wikipedia.org/wiki/Tsunami > http://www.ess.washington.edu/tsunami/index.html > http://www.volcanolive.com/tsunami10.html > http://serc.carleton.edu/NAGTWorkshops/visualization/collections/tsunami.html
