eqhazards&risks

eqhazards&risks - EQ Hazards Risks EENS 204 Tulane...

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This page last updated on 21-Jan-2004 EENS 204 Natural Disasters Tulane University Prof. Stephen A. Nelson Earthquake Hazards and Risks Earthquake Risk z Many seismologists have said that "earthquakes don't kill people, buildings do". This is because most deaths from earthquakes are caused by buildings or other human construction falling down during an earthquake. z Earthquakes located in isolated areas far from human population rarely cause any deaths. z Thus, earthquake hazard risk depends on 1. Population density 2. Construction standards (building codes) 3. Emergency preparedness Examples: z Worst earthquake in recorded history occurred in 1556 in Shaaxi, China. Killed 830,000 people, most living in caves excavated in poorly consolidated loess (wind deposited silt and clay). z Worst earthquake in this century also occurred in China (T'ang Shan Province), killed 240,000 in 1976. Occurred at 3:42 AM, Magnitude 7.8 Earthquake and magnitude 7.1 aftershock. Deaths were due to collapse of masonry (brick) buildings. z Contrast - In earthquake prone areas like California, in order to reduce earthquake risk, there are strict building codes requiring the design and construction of buildings and other structures that will withstand a large earthquake. While this program is not always completely successful, one fact stands out to prove its effectiveness. In 1989 an earthquake near San Francisco, California (The Loma Prieta, or World Series Earthquake) with a Richter Magnitude of 7.1 killed about 62 people. Most were killed when a double decked freeway in Oakland collapsed. About 10 months later, an earthquake with magnitude 6.9 occurred in Armenia, where no earthquake- proof building codes existed. The death toll in the latter earthquake was about 25,000! z Computer simulations for large cities, like San Francisco or Los Angeles, California, indicate that a magnitude >8.0 earthquake would cause between 3,000 and 13,000 deaths. { 3,000 if at night, when populace is asleep in wood frame houses { 13,000 if during day when populace is in masonry buildings and on freeways. 1/21/2004 Page 1 of 6
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Architecture and Building Codes While architecture and building codes can reduce risk, it should be noted that not all kinds of behavior can be predicted. z Although codes are refined each year, not all possible effects can be anticipated. For example different earthquakes show different frequencies of ground shaking, different durations of ground shaking, and different vertical and horizontal ground accelerations. z Old buildings cannot cost-effectively be brought up to code, especially with yearly refinements to code. z Even with construction to earthquake code, buildings fail for other reasons, like poor quality materials, poor workmanship, etc. that are not discovered until after an earthquake.
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This note was uploaded on 11/20/2010 for the course LIR 30 taught by Professor Thornley,k during the Spring '08 term at Santa Rosa.

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eqhazards&risks - EQ Hazards Risks EENS 204 Tulane...

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