Seismic Hazards Flashcards
The nature and cause of seismic hazards …
a sudden violent shaking of the ground as a result of the movements within the earth’s crust
As the crust of the earth is constantly moving, there tends to be a slow build up of stress, within the rocks. When the pressure is released, parts of the surface experience for a short period, an intense shaking motion.
The distribution of seismic hazards is …..
The vast majority of earthquakes occur along plate boundaries, the most powerful being associated with destructive margins. At conservative margins, the boundary is marked by transform faults and sudden differential movements along these faults produce earthquakes
it has been suggested that human activity could cause minor earthquakes, through building large reservoirs which puts pressure on the underlying rocks, or subsidence of deep mine workings
The magnitude and frequency of seismic hazards is …..
MMS
Good at showing quantitative measure - can compare data with clear comparisons
It doesn’t tell you about the hazards to humans
Mercalli Scale
Meaningful description of hazard intensity - can compare impacts
It doesn’t link damage to characteristics of place which can lead to a weak understanding of the event
Primary effects …..
Ground shaking severity dependant on magnitude, depth, distance from the epicentre and local geological conditions
Ground rupture: breaking and displacement of the Earth’s surface, usually along a fault line. Is a risk to large engineered structures
Secondary effects ……
Soil liquefaction: when shaken soils with high water content lose their mechanical strength and behave like a liquid
- Landslides/avalanches: slope failure because of ground shaking
- Tsunamis: giant sea waves generated by shallow-focus point
- Fires: resulting from broken gas pipes and collapsed electricity lines
- Effects on people and the built environment: e.g. destroyed/damaged infrastructure; destroyed provision of electric, water, gas; flooding; disease; food shortages; disruption to the local economy etc.
Environmental effects ……
Political effects ….
Social effects …..
Economic effects …..
Responses to seismic hazards …..
Name of lower HDI country Case study:
Haiti, 2010
Haiti, Facts:
Characteristics of place?
Characteristics of hazard
Primary / secondary effects
Risk / vulnerability
Short / long term response
Charactertics of place
- dense informal settlements
- fatalstic attitude
- poorest country in western heisphere
- high poverty (19% access to sanitation)
- corrupt government
Characteristics of hazard
- 7MMS
- destructive plate boundary
- focus 13km
- 50 aftershocks
Primary effects
- 220,000 deaths
- 2.3 million made homeless
- 188,000 builidings collapsed
Secondary effects
- aid delayed
- collapse of water supplies, resulted in lack of sanitation, which led to spreads of diseases (8,000 died of cholera)
- landslides and liquefaction
Vulnerable
- large history of national debt
- extreme poverty
- poor housing conditions (no building codes )
Long term response
- new building codes
- 50% of debris removed by 2014
- some national debt written off
Short term response
- UK sent search and rescue dogs to look for survivors
- US deployed 3,500 soldiers to use heavy lifting machinery
- mass graves dug for bodies
Name of HIgher HDI seismic hazard case study?
South Napa, California
South Napa, California Facts:
Characteristics of place / hazard
Primary / secondary events
Risk / vulnerability
Long/ short term response
Characteristics of place?
- excellent public services
- hazard perception - adaption
- well planned residential zones
- stable government (building codes enforced)
Characteristics of hazard?
- 6 MMS
- conservative boundary
- focus 11km
- 12 aftershocks
Primary
- 1 death
- 120 injured
- significant damage to some commercial buildings
Secondary
- 6 major fires
- $500 million damages
- power outages for 69,000
- 30 water mains broken
Vulnerable
- low vulnerability ( high HDI)
- stable and reliable government prepared to respond
- drills in schools (education)
- aseismic design and retrofitting (adaption)
-
Short term response
- aid
- evacuation of residents in damaged housing
- Obama declared major disaster
Compare case studies…….
Do the hazard characteristics best explain the difference?
Not the best explanation but explains the hazard characteristic to an extent.
Haiti was higher on the MMS scale by 1, but suffered over 11 billion in damage while Napa suffered less than 10% of that damage (36.2 million)
Do the characteristics of the people/place best explain the difference?
best explanation is the preparedness and vulnerability of an area
A HIC will have more money to invest in aseismic designs of buildings and putting building codes in place
A LIC will not have the same amount of money to invest into community preparedness. Therefore will be vulnerable
Haiti had a fatalistic attitude while Napa focused on preparedness and adaptation
