GLG Physical Geology Bob Leighty Earthquakes

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, Dr. Bob if you have any questions about today’s lecture Leave no questions behind! Explore and have fun! 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.

What’s Shakin’? Earthquakes  National Earthquake Information Center (NEIC)NEIC World seismicity

 Destructive (in lives & property) Mexico City (1985) Earthquakes: why do we care? Earthquakes

 Some types of building sites are better than others Earthquakes: why do we care? Earthquakes > Bedrock is better than soft sediment

 We can learn about the Earth's interior & tectonic platestectonic plates Earthquakes: why do we care? Earthquakes

 Elastic rebound theory - Stress builds up until rocks deform elastically and then break, releasing energy Elastic rebound theory  The size of a quake  the amount of built-up stress What is an earthquake? Earthquakes  Quake = A sudden release of stored energy causing vibrations (seismic waves) in rock Quake

 Mostly occur at plate boundaries (~95%)  Originate within the brittle part of the lithospherelithosphere Where do earthquakes occur? Earthquakes

 Focus - The actual location within the Earth where the earthquake originates  Epicenter - The point on the Earth's surface above the focus Epicenter Where do earthquakes occur? Earthquakes

 Fastest (4 to 7 km/sec)  Can move through solids & liquids P-waves Seismic Waves Earthquakes Body Waves  P-wave = primary wave or compressional wave P-wave

 Slower (2 to 5 km/sec)  Can move only through solids S-waves Seismic Waves Earthquakes Body Waves  S-wave = secondary wave or shear wave S-wave

 Seismometer - Detects and records vibrations (earthquakes, nuclear blasts, etc.) Seismometer Locating Earthquakes Earthquakes

 Seismogram - Record of vibrations (paper, electronic) Seismogram Locating Earthquakes Earthquakes

P S surface lag time Locating Earthquakes 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 Locating Earthquakes Earthquakes

Magnitude  Richter Scale = measures earthquake intensity (energy) from ground shaking Richter Scale  Determined by measuring amplitude (height) of the S-wave on seismogram  Richter scale is logarithmic (each interval x10) Earthquake Intensity Earthquakes  Seismic Moment Scale - A better estimate of earthquake energy, now the standard Seismic Moment Scale

 Duration of earthquake  Population density  Distance from focus / depth of earthquake  Soft sediment vs. dense bedrock Controls on Earthquake Damage Earthquakes  Building design and construction

Ground Rupture Destructive Effects Earthquakes

Ground Rupture Destructive Effects Earthquakes

 Liquifaction - Soft sediment can amplify vibrations (water- saturated sediment can liquefy & turn to goop) LiquifactionLiquefaction Destructive Effects Earthquakes

 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 killedFire Destructive Effects Earthquakes

 Tsunami - Caused by the sudden displacement of water Tsunami  NOT a tidal wave Tsunami Destructive Effects Earthquakes

 Fast, but low in open ocean  Big & bad near shore (average up to 30 m high) Tsunami Destructive Effects Earthquakes

Tsunami Earthquakes

Destructive Effects Earthquakes

Tsunami Earthquakes

WWW Links in this Lecture > NEIC - > Tectonic plates - > Elastic Rebound Theory - > Earthquake - > Lithosphere - > Epicenter - > Seismic waves - > P-wave - > S-wave - > Seismometer - > Seismogram - > Richter Scale - > Liquifaction - > Tsunami - > > >