Module 2_ EQs

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University Of Arizona *

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103

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Geography

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Feb 20, 2024

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pdf

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4

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Module 2: EQs Define the three characteristics of a wave Amplitude- displacement Wavelength- distance between successive waves period/frequency-P is time between waves (=1/frequency) ; F is number of waves per time (Hertz=1 sec) What are the 3 types of seismic waves? Which is fastest? Which is most destructive? - Primary wave, Secondary wave, Surface wave. The fastest wave is the Primary wave. The most destructive wave is a Surface wave. It causes the most damage. What is a seismograph? - A seismograph is the record of ground motion produced by the earthquake. . What do these waves tell us about layers of Earth? - The waves tell us what the different densities and velocities are in the different layers of the earth due to the earthquake's speed. How do you locate the source of an EQ? How many stations do you need (at least)? - P waves travel about 1.7 times faster than S waves. Farther from hypocenter, greater lag time of S wave behind P wave (S-P). (S-P) time indicates how far away the earthquake was from the station using the three seismic stations. Must determine distance of EQ from at least three seismic stations, P wave arrives, then S wave arrives, and lastly Surface wave arrives last, this intersection of the circles gives the location. What is the relationship between earthquake numbers and magnitude? - The relationship between earthquake numbers and magnitudes is found using logarithms with a low magnitude causing a high frequency, and a high magnitude causing a low frequency. What is the difference between mainshock and aftershock? - The mainshock is the biggest event to occur and the aftershocks are smaller events that continuously happen close together after the mainshock which then trails off. What do you need to determine magnitude on Richter Scale? - The magnitude on the Richter scale is a logarithmic scale that combines the S-P time movements and the amplitude to find the magnitude scale in the middle. What is Richter scale good for? Bad for? Why bad?
- Richter scale is good for magnitude of shallow, small moderate nearby earthquakes. It does not work well for distant or large earthquakes, this is because it cant accurately calculate the magnitude due to the farther distance of the earthquake. What is the difference between magnitude and intensity? - The difference between magnitude and intensity is the magnitude of an EQ is a measure of how big it is-how much energy is released compared to the Intensity (Modified Mercalli) of an EQ which is a measure of how much shaking occurs at any place and how much damage it does. What kind of shaking does massive damage to buildings? Why? - Horizontal shaking does massive damage to buildings, because of the side to side motion as well as acceleration this furthers damage because of how buildings are designed to only handle vertical forces (weight of building and contents). What level in the Modified Mercalli Intensity does damage possibly start to create many loss of lives on a poor country (i.e. Haiti)? - Weak buildings suffer more damage from horizontal accelerations of more than 0.1g (=0.98 m/s^2) What ground type is most destructive in terms of wave energy? - The ground type that is most destructive in terms of wave energy is the water-saturated sand and mud (softer ground) What is liquefaction? What happens to large structures during liquefaction? - Liquefaction is water saturated soils that become a slurry (liquid-like) when shaken. Buildings that can tilt, sink and fall. How does the natural period of swaying change for different heights of buildings? - Natural Periods of swaying are about 0.1 second per story. 1- story houses shake at about 0.1 second per cycle (short period=fast=high frequency). 30-story buildings sway at about 3 seconds per cycle (long period=slow=low frequency). How tall of a building would you prefer to be in during an earthquake? - I would prefer to be in a modern 1-2 story wood frame house with shear walls, bracing , tying walls, and foundations and roof together. What lacking structure in building properties causes building floors and elevated highways to collapse?
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