GEOL 1425 1st Edition Lecture 17 Outline of Last Lecture I. Geosystem interactionsII. Volcanism and human affairsIII. ReviewOutline of Current Lecture I. About earthquakesII. Studying earthquakesCurrent Lecture—Earthquakes I. About earthquakesa. Occur where plates converge, split apart, and slide past each otherb. Sequence of events can often be complex, making earthquake prediction difficult—false positives and negativesII. What is an earthquake? Plate movements generate forces in narrow zones at the boundaries between tectonic plates. The buildup of energy does not get released immediately. But when the fault slips, the stress is reduced, dropping to a level below the rock strengtha. Forces: stress—happens when the rock is under pressure; the force per unit area that causes rocks to deform, the relative amount of deformation. Before an earthquake the rock may be stressed until it reaches its breaking point. b. Forces: strength—whatever holds 2 blocks of rock together (cohesion) breaks and moves apart, slips, falls. c. Elastic rebound theory-- the stress is suddenly released and there is a reboundThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.d. Fault rupture: epicenter (place on ground surface above focus) and its focus (point where slip begins, action here)III. Studying earthquakesa. Time delay between seismic station recoding and the actual time of earthquakeb. P waves (initial) = compression waves are compressed and expanded. Push/pull. c. S waves (secondary)= much slower, shear waves, displace materials at right angles to path of travel, do not exist in liquids or gassesd. Surface waves= confined to surface, like waves on an ocean on rocks of surface,slower than S wavese. Locating the earthquake epicenter: often in remote places and predictions of outcomes become very difficult since you have to determined center of earthquake. Need at least 3 seismographs across the globe in order to do this. f. Earthquake’s magnitude determines the intensity of waves and potential destructiveness. **Richter magnitude: not a linear scale! Energy releases increases even more with earthquake magnitude by a factor of 33 for each Richter unit. ** Know for test::Epicenters and fociDepth of earthquakesRecording earthquakesP-, S-, and surface wavesThe richter scale—difference in magnitudesLoss of life and earthquakesSilent earthquakesRecurrence interval for seismically active
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