Textbook Notes (362,790)
EAS205 (28)
Chapter 4

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School
University of Alberta
Department
Earth and Atmospheric Sciences
Course
EAS205
Professor
Solweig Balzer
Semester
Fall

Description
CHAPTER 4EARTHQUAKESImportant Concepts1An earthquake occurs when movement along a fault zone results in a sudden release of builtup strain energy in the lithosphereMost earthquakes occur at plate boundaries2The point of first break or movement along a fault is called the earthquakes focus or hypocenterThe point on the earths surface directly above the focus is called the epicenter3There are several types of earthquake or seismic wavesaP primary waves are compressional waves that cannot travel through the earths liquid outer corebS secondary waves are shear waves and cannot travel through the earths coreBoth P waves and S waves are classified as body waves because they travel through the earths interiorcSurface waves travel along the earths surface some causing vertical ground motions and others horizontal shearing motionsMuch of the structural damage during earthquakes is caused by the surface waves4P waves travel faster than S wavesThe difference in the first arrival times of P waves and S waves as detected by seismographs is a function of the distance to the earthquakes epicenterThe epicenter of an earthquake can be determined from SP time difference recorded at three or more seismograph stations5The magnitude of an earthquake is a measure of the amount of ground displacement or shaking associated with the earthquake and is usually reported using the Richter magnitude scale although moment magnitude is a better measure of the released energyThe Richter scale is logarithmic6 The intensity of an earthquake is a measure of the damaging effects of an earthquake at a particular location and is usually reported on the Modified Mercalli scaleThe damage caused by an earthquake depends not only on its magnitude but also on other factors such as the distance from the epicenter the integrity of the structures and their foundations and population density7Earthquakerelated hazards includeaGround shaking and fault displacementbGround failures including landslides and liquefactionLiquefaction is a quicksand condition arising in wet soil shaken by seismic wavescTsunamis or seismic sea waves and coastal floodingdFires caused by fuel line and storage tank ruptures and electrical system damage8Some progress in earthquake prediction and forecasting has been made by recognizing the presence of seismic gaps and by studying precursor phenomena and earthquake cyclesUnfortunately it is not yet possible to precisely predict the timing size or precise location of a future major earthquake24
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