Natural Hazards Flashcards
The Hazard Management Cycle
1 Prevention and mitigation
2 Preparedness
Incident
3 Response
4 Recovery
Slab Pull
-Subduction boundary
-Denser, heavier plate subjects beneath the less dense plate
-Edge of subducting plate colder and heavier than mantle, continues to sink, pulling rest of plate with it
-Force that sinking plate exerts on rest of plate is called slab pull
What else can Cause an Earthquake?
-Subsidence as a result of deep mining
-Pressure on surface rocks from water in a reservoir
-Hydraulic fracturing or ‘fracking’ - a drilling process that injects gallons of water, sand and chemicals under high pressure into a well, cracking the rock and to release natural gas and oil
Intrapolate Earthquakes
Example: UK
-Caused by isostatic readjustment
-Smaller scale earthquake
-Many faults caused by turbulent geological past
-Faults are where they occur
-Driving force: regional compression, uplift
-20-30 a year (in UK)
-Low magnitude
Factors Determining Extent of the Earthquake Hazard
-Level of development and GDP
-Depth of focus
-Population density
-Type of plate boundary
-Magnitude
-Location and landscape
-Intrapolate
-Frequency of earthquake
-Distance from epicentre
Designing Earthquake - Resistant Infrastructure
-New infrastructure can be specially designed to withstand small tremors e.g. cross-bracing, shock absorbers, shear walls
-The Transamerica Pyramid in San Francisco ($75m)
Limitation
-LDCs cannot afford to construct
-More than 1.8m older buildings cannot withstand earthquake tremors in Tokyo
Strengthening Existing Infrastructure
-Designed to withstand strong tremors
-Can be reinforced by wrapping steel frames around pillars/placing steel rods
Example: fireproof materials and automatic shut-off valves installed into gas pipes
Limitation
-Strengthened may not be as strong as new
-1994 Northridge earthquake, USA, many strengthened with steel frames badly damaged, new remained undamaged
Preparedness, Adaptation, Mitigation
-Build new infrastructure away from earthquake prone areas to reduce economical damage
-Authorities can implement guidelines on location and height of buildings
-USA use earthquake risk maps for land use
Limitation
-Difficult in cities of developing countries
-Poverty causes migrants to construct houses illegally
How can Natural Hazards Affect People?
-Can change population size
-Can increase risk of flooding
-Local events can have global impacts
-Loss of life, property damage
Factors Causing Hazard Perception to Vary
-Determined by effect it may have on our lives
-Advantages may outweigh risks
-Level of development
-Age, social status, religious beliefs can determine factors for evacuation
-People tend to respond in ways that are consistent with their perception of risk
-Level of education of community
The Park Model
Stage 1: modifying cause and event
Stage 2: hazardous event
Stage 3: search, rescue and care
Stage 4: relief and rehabilitation period
Stage 5: nature of recovery related to:
-The need to reduce vulnerability
-The need to restore normality as soon as possible
Why is the Depth of the Focus Important?
The higher the focus is, the more likely it will be a destructive earthquake as the seismic waves don’t have far to go
Richter Scale (Charles Richter, 1932)
-Measures magnitude of earthquake
-Measured with seismometer, records extent of ground movement
-‘Movement magnitude scale’
Advantages: accurate, easy to compare
Disadvantages: doesn’t say impacts
Mercalli Scale (Giuseppe Mercalli, 1902)
-Uses observations of people who experienced the earthquake to measure intensity
Advantages: says the impacts
Disadvantages: subjective to opinion
Education on Emergency Procedure
-Earthquake drills conducted regularly in many earthquake-prone countries
-Governments use posters and signs to warn people about areas prone to the effects
Limitations
-People tend to be complacent and may not see the importance
-Residents in Tokyo are less prepared than other parts of Japan, occurred more than 80 years ago
