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Virginia Tech - GEOS 1034 - Class Notes - Week 3

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Virginia Tech - GEOS 1034 - Class Notes - Week 3

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background image Liquefaction- intense shaking that causes near-surface layers of water-saturated sand to  change rapidly from solid to liquid • Shaking temporarily turns wet sediments into a fluid ○ Solution: put pilings into bedrock to stabilize structure Earthquake Prediction and Mitigation 1976 M7.8 Tangshan, China Earthquake 240,000 deaths- predicted 500,000 Population was greater Earthquake was at 3AM when most people were asleep in buildings Took 2 days before outside help arrived No foreign assistance allowed by Chairman Mao China has a history of minimizing official casualty rates for political  reasons 2010 M7 Haiti Earthquake 100,000-200,000 people killed • Earthquake Early Warning system ○ Seismic waves travel slower than speed of light so we can detect an  earthquake and communicate a warning ahead of shaking • Earthquake clock- possible to warn people about earthquakes because we know  how fast seismic waves travel NOT predictable Faults are generally steadily loaded Do not occur at same stress level We can't easily measure stresses in earth  § Not the same magnitude Parkfield Experiment proved that earthquakes are not predictable to the year or  magnitude Historical record can help us estimate probability of future earthquakes No reliable earthquake precursors Foreshocks- smaller than earthquakes and only sometimes occur  before a much bigger mainshock § Aftershock- smaller earthquakes that always occur after a bigger  mainshock § Fire Rainbows- occur when sunlight enter flat, hexagon shaped ice  crystals gets split into individual colors § GPS measurements enable us to measure slip deficit rates- 12 mm/year that  cannot be explained Allow us to predict how big an earthquake will likely be Knowing slip deficit rate and time since last earthquake enables a  forecast of potential size of next earthquake Ex: Haiti earthquake predicted to be 7.2 and 7.0 earthquake in  that region § GPS needs open sky view, battery,  We need to spread awareness about earthquakes Educate public Do not build near active faults, especially on loose soils Build earthquake resistant structures Develop earthquake early warning systems Earthquakes Wenchuan, China- 7.9, 83,000 died ○ Over 7,000 poorly built schools collapsed, killing about 10,000 students
○ Brave police officers were able to save several children before a landslide 
further demolished the school Haiti
• 2005 Kashmir earthquake
○ Concrete floors are heavy and w/o proper steel reinforcement and lateral  support can lead to pancake during an earthquake Biggest earthquakes occur: on subduction zones Largest stress buildup Longest faults Deadliest earthquakes occur: Happen on interior plates Largest populations Bad building practices What to do in an earthquake? If indoors in a well engineered building Stay indoors Drop to the ground; take cover under a table Stay away from glass and anything that could fall Use a doorway for shelter only if you know it's a strongly supported,  loadbearing doorway DO NOT use elevators If indoors in a poorly constructed building Get out of building as fast as possible If outdoors Stay outdoors, move away from buildings How to build an earthquake resistant structure • Diagonal beams provide resistance to shearing that often causes buildings to  collapse ○ Shearing- one beam gets shorter and one gets longer • Put in corner studs to improve stability • In sediment, put pilings down into bedrock to stabilize • Isolation system ○ Building with rubber laminations to steel shim plates to allow the building  to withstand shearing • Inertial damping systems ○ Allows building to sway around weighted material Earthquakes can break if too much shaking • Forced Resonance: when the frequency of external forces matches the natural  frequency of a structure, the structure will swing wildly ○ Collapse of Tacoma Narrows bridge in 1940 from wind induced forced  resonance Week 3 (9/5, 9/7) Monday, September 3, 2018 4:57 PM
background image Liquefaction- intense shaking that causes near-surface layers of water-saturated sand to  change rapidly from solid to liquid • Shaking temporarily turns wet sediments into a fluid ○ Solution: put pilings into bedrock to stabilize structure Earthquake Prediction and Mitigation 1976 M7.8 Tangshan, China Earthquake 240,000 deaths- predicted 500,000 Population was greater Earthquake was at 3AM when most people were asleep in buildings Took 2 days before outside help arrived No foreign assistance allowed by Chairman Mao China has a history of minimizing official casualty rates for political  reasons 2010 M7 Haiti Earthquake 100,000-200,000 people killed • Earthquake Early Warning system ○ Seismic waves travel slower than speed of light so we can detect an  earthquake and communicate a warning ahead of shaking • Earthquake clock- possible to warn people about earthquakes because we know  how fast seismic waves travel NOT predictable Faults are generally steadily loaded Do not occur at same stress level We can't easily measure stresses in earth  § Not the same magnitude Parkfield Experiment proved that earthquakes are not predictable to the year or  magnitude Historical record can help us estimate probability of future earthquakes No reliable earthquake precursors Foreshocks- smaller than earthquakes and only sometimes occur  before a much bigger mainshock § Aftershock- smaller earthquakes that always occur after a bigger  mainshock § Fire Rainbows- occur when sunlight enter flat, hexagon shaped ice  crystals gets split into individual colors § GPS measurements enable us to measure slip deficit rates- 12 mm/year that  cannot be explained Allow us to predict how big an earthquake will likely be Knowing slip deficit rate and time since last earthquake enables a  forecast of potential size of next earthquake Ex: Haiti earthquake predicted to be 7.2 and 7.0 earthquake in  that region § GPS needs open sky view, battery,  We need to spread awareness about earthquakes Educate public Do not build near active faults, especially on loose soils Build earthquake resistant structures Develop earthquake early warning systems Earthquakes Wenchuan, China- 7.9, 83,000 died ○ Over 7,000 poorly built schools collapsed, killing about 10,000 students
○ Brave police officers were able to save several children before a landslide 
further demolished the school Haiti
• 2005 Kashmir earthquake
○ Concrete floors are heavy and w/o proper steel reinforcement and lateral  support can lead to pancake during an earthquake Biggest earthquakes occur: on subduction zones Largest stress buildup Longest faults Deadliest earthquakes occur: Happen on interior plates Largest populations Bad building practices What to do in an earthquake? If indoors in a well engineered building Stay indoors Drop to the ground; take cover under a table Stay away from glass and anything that could fall Use a doorway for shelter only if you know it's a strongly supported,  loadbearing doorway DO NOT use elevators If indoors in a poorly constructed building Get out of building as fast as possible If outdoors Stay outdoors, move away from buildings How to build an earthquake resistant structure • Diagonal beams provide resistance to shearing that often causes buildings to  collapse ○ Shearing- one beam gets shorter and one gets longer • Put in corner studs to improve stability • In sediment, put pilings down into bedrock to stabilize • Isolation system ○ Building with rubber laminations to steel shim plates to allow the building  to withstand shearing • Inertial damping systems ○ Allows building to sway around weighted material Earthquakes can break if too much shaking • Forced Resonance: when the frequency of external forces matches the natural  frequency of a structure, the structure will swing wildly ○ Collapse of Tacoma Narrows bridge in 1940 from wind induced forced  resonance Week 3 (9/5, 9/7) Monday, September 3, 2018 4:57 PM

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School: Virginia Polytechnic Institute and State University
Department: Geoscience
Course: Geoscience
Professor: Ying Zhou
Term: Fall 2018
Tags:
Name: Earth's Natural Hazards Week 3
Description: earthquake prediction and how to make structures more earthquake resistant
Uploaded: 09/07/2018
3 Pages 23 Views 18 Unlocks
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