4.1 Earthquake Management Flashcards
What is preparation?
The hazard is going to happen, what can we do to reduce the risk:
Clear evacuation routes to safe zones
Early warning system -> seismic monitoring
Strict building codes and earthquake proof buildings -> base isolation bearings, energy dissipation devices and counter weights
Build on solid bedrock
Earthquake drills and education about risks from a young age
Well trained emergency services
Good infrastructure
What is prediction?
What are the different methods of prediction?
Calculating When and where a hazard is going to occur Seismic History Seismic Gap Theory Ground Water Levels Ground deformation Radon gas emissions
Explain seismic history as a predictor?
An area with a large previous quake is likely to have another in future
Foreshocks show stress on a fault - can predict a future large quake
Explain seismic gap theory as a predictor?
Along a fault each segment should have similar activity
If one zone has much less activity it is likely to have a bigger quake
If less activity it means stress is not being released
Eg Loma Prieta Gap in 1989
Explain ground water levels as a predictor?
Stress builds causing micro fractures in rocks
Alters porosity and permeability
Changes ground water level
Electrical resistance changes with ground water levels in rocks
Explain ground deformation as a predictor?
Before a fault ruptures as a quake the earth could bulge and deform Measured by: GPS EDM (electronic distance measurement) Tiltmeters
Explain radon gas emissions as a predictor?
Radon is a naturally occurring gas from uranium decay deep in the earth
Radon collects on deep fault planes
As the stress fractures the rock, radon gas escapes to surface which is a warning of the stress
What is the park field experiment?
Research project into earthquake activity in San Andreas fault
Hoped to predict earthquakes from past quakes in 1857 onwards
Estimated next one was 1993 but only happened 2004
Collected geological, seismic, magnetic and other details
Improved our ability for short term earthquake predictions
What are the common methods of designing earthquake proof buildings?
1 flexible foundation 2 counter forces with damping 3 vibration shields 4 reinforced building structures 5 earthquake resistant materials
Explain flexible foundations?
Steel, rubber and lead are used as flexible foundation isolators as building is raised above them
Shockwaves cause the isolators to vibrate and not the building
Isolators absorb seismic waves and shock waves do not travel through the building
Explain counter forces with damping?
Shock absorbers like in a car reduce magnitude of shock waves
Use vibrational (a) control devices and (b) pendulum dampers.
A. Piston filled with silicone oil - Dampers laid at every level between column and beam. Shock energy closes pistons into oil and energy dissipated as heat
B. Skyscrapers. Large ball suspended with steel cables, hydraulic system. Shock waves make the ball move opposite to building direction and limiting movement.
Explain vibration shields?
Deflects not counteracts shock waves
Seismic invincibility cloak of 100 concentric plastic and concrete rings buried beneath foundation of building.
Deflects energy away through the rings not the ground
Explain reinforce building structure?
Buildings designed to spread shock waves force using:
Shear walls - panel walls keep building in shape even when moving
Cross braces - steel beams support compression and tension
Diaphragms - floors, roofs, decks reduce tension and push shock waves to vertical sides of building
Movement resisting frames - frames in joints allow columns and beams to bend while joints can remain rigid
Explain earthquake resistant materials?
Steel and wood - ductile so comes with tension and deforms, buildings can bend without breaking. Wood has high strength and light
Innovative material - shape memory alloys absorb shock and revert to original shape
Natural substances eg Sticky mussel fibre and Bamboo
