Презентація на тему «Natural Hazards»

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Introduction to Natural Hazards
geo-process
humanprocess
Hazardousconditionor result
Why is the human element so critical?
CANNOT stop the geologic processesCANNOT stop the population growth/expansion
Therefore, we must try to reduce (mitigate) the hazards through:scientific studypopulation educationchanges in engineering/building practicesmanagement plans and hazard response scenarios
Earthquakes and Tsunamis
San Francisco - Great Earthquake
Magnitude 7.7 - 8.3
Earthquake Hazards
 These are important hazards to understand:the natural hazard that on average kills the highest number of people per year (> 1 million during the past century) commonly strikes without warning no time for evacuation not a predictable trend to earthquake numbers, magnitude or location 1000's of large earthquakes every year ~ 20 are > M7.0 and these account for 90% of the energy released and 80% of all the fatalities 
How do we mitigate the hazard from earthquakes?
Reinforce buildingsEducationDisaster plan
An earthquake under the ocean has the potential to form a tsunami.The earthquake must vertically displace overlying water (extensional or compressional faults - not transform)
Extension
Compression
Transform
How does an earthquake form a tsunami?
2004 South Asian Boxing Day event
Biggest earthquake in 40 years!Magnitude 9.2150 km off the west of Northern SumatraGenerated a disastrous tsunami in 12 countries
The earthquake occurred at a convergent tectonic plate boundary (subduction zone)An estimated 1,600 km (994 miles) of faultline slipped about 15 m (50 ft)!The earthquake released 20 x 1017 Joules of energyEquivalent to:475,000,000 kg of TNT23,000 Hiroshima atomic bombs!
Second largest recorded earthquake
A village near the coast of Sumatra lays in ruin after the tsunami.
How do we mitigate the hazard from tsunamis?
Monitoringprocess is very technology-intensivehigh costs for many poorer countriesoften no technology available to monitor local tsunamisfor example,Papua New Guinea has no monitoring stationsreliant on the Pacific Tsunami Warning Centertsunami in 1998 was not detected
Seawall construction cause early wave breakingprevent wave run up into urban areas 
How do we mitigate the hazard from tsunamis?
Educationwarning systemsevacuation plansgeneral understanding of the hazards involved
PunishmentFrom God 45%
Natural event35%
Bomb 20%
Population reaction: Papua New Guinea (1998)
How do we mitigate the hazard from tsunamis?
Tropical Storms
Same Storm - Different Name
Most widespread destructive weather hazard For example: Hurricane Floyd (1999) only a moderate level hurricane caused US$5.6 billion in damage in the Bahamas and North Carolina (USA) and 57 fatalities 
Tropical Cyclones
(Left) Three different cyclones spinning over the western Pacific Ocean on August 7, 2006.
How do cyclones form?
The above figure shows how cyclones form. The green arrows show where warm air is rising. The red arrows indicate where cool air is sinking. 
Cyclone Categories
Category
Wind Speed (mph)
Damage at Landfall
Storm Surge (feet)
1
74-95
Minimal
4-5
2
96-110
Moderate
6-8
3
111-130
Extensive
9-12
4
131-155
Extreme
13-18
5
> 155
Catastrophic
19+
The Saffir-Simpson Hurricane Scale
Hurricane Katrina
Hurricane Katrina was the most costly and most deadly hurricane in the history of the USA.Category 5At least 1,836 fatalitiesDamage estimated at US$ 81.2 billion
Hurricane Katrina
What damage is produced?
Storm Surgewater that is pushed toward the shore by the force of the cyclone winds.
What damage is produced?
Windresponsible for the loss of power and utilitieswind damage affects larger areas than surgeflying debristree loss
What damage is produced?
Flying debrisdebris propelled at high speeds
How do we mitigate the hazard from a cyclone?
Monitoringearly warning systemsInfrastructurecyclone wallscommunal sheltersEducation and planning
Natural Hazards Summary
Graph showing the number of deaths per year due to natural hazard events
Before and After photographs from Phuket, Thailand, of the 2004 Boxing Day (26th of December) tsunami.
The next parts of the lecture will provide details and give examples of a number of specific natural hazards.We will first look at earthquakes and and tsunamis generated by earthquakes.
The San Francisco earthquake of 1906 was a major earthquake that hit San Francisco and the coast of northern California on Wednesday, April 18, 1906. The most widely accepted estimate for the magnitude of the earthquake is 7.8; however, other values have been proposed from 7.7 to as high as 8.3. The epicenter occurred offshore, about 2 miles (3 km) from the city. It ruptured along the San Andreas Fault for a total length of 296 miles (477 km).The earthquake and resulting fire is remembered as one of the worst natural disasters in the history of the USA. The death toll from the earthquake and resulting fire represents the greatest loss of life from a natural disaster in California's history. The economic impact has been compared with the more recent Hurricane Katrina disaster.Presenter: Refer to the photos to show the large scale of the damage.
Photographs showing examples of the destruction caused by earthquakes.
This cartoon diagram summarises how an earthquake may form a tsunami.Shows normal conditions. Note the presence of a pre-existing crack or fault in the seafloorThe earthquake! An earthquake causes a piece of the seafloor to be pushed up into the overlying ocean. This causes the water to also be displaced/pushed up.The displaced water forms tsunami wave that can travel thousands of kilometres before it reaches land. The wave will break when it does eventually reach the shore potentially causing flooding as the water level rises well above normal sea level.Mud, sand and a trail of debris (trees, building material etc) is left deposited on the sea shore after the wave has subsided.
You most probably remember the 2004 South Asian Boxing Day tsunami event. This tsunami was caused by an earthquake off the coast of Sumatra that measured a magnitude of 9.2!! The biggest earthquake recorded in 40 years!Presenter: Can ask the students if they saw the aftermath of the tsunami on the television and what they remember of the images.
The earthquake off the Sumatran coast was originally recorded as 9.0 but has been increased to 9.2. At this magnitude it is the second largest earthquake ever recorded. This earthquake was also reported to have the longest duration of faulting, lasting between 500 and 600 seconds (8.3 to 10 minutes).The earthquake was so large that it caused the entire planet to vibrate as much as half an inch, or over a centimetre!!It occurred at a convergent (Presenter: remember the diagram of the convergent fault) tectonic plate boundary, where an estimated 1,600 km of faultline slipped about 15 m (a LOT of rock moved!).The earthquake released 20 x 1017 Joules of energy, which is like setting off 475 million kilograms of TNT or 23,000 atomic bombs!!NOTE: The largest earthquake ever recorded, which measured 9.5, was in Chile on May 22, 1960.
The tsunami caused widespread flooding and fatalities. Thousands of people died and many more were displaced from their homes. This photo shows an example of the devastation caused by the waves.
Finally, to protect the population against tsunamis they need to be educated about the hazards involved and warning systems (sirens, emergency service teams) and evacuation plans (escape to higher ground) need to be established.
Damage from Hurricane Katrina in Louisiana.Left photo: Flooded motorway and surrounding suburbs in New Orleans.Top right: Bridge damage caused by Katrina - each section of the road has collapsed.Bottom right: 16 foot (5 m) and higher waves pushed over 23 shrimp boats and the cargo ship named "Caribbean Clipper" (pictured with all of the cars on it) onto shore, along with over 6 fishing boats aground (4 shown). The captain of the 179 foot (55 m) cargo ship M/V Caribbean Clipper rode out Katrina on board the ship! The ship was returned to sea, six months later, using a large crane to unload the cargo and re-float the hull.
Destruction from strong winds will effect a wider region than that damaged by the storm surge. The wind can uproot trees, bring down powerlines, and damage properties.NOTE: The sheet of corrugated iron wrapped around the tree in the bottom photograph.