Natural Disasters

What is an Earthquake? Ground movement caused by the sudden release of seismic energy due to tectonic forces. The focus of an earthquake is the actual location of the energy released inside the Earth’s crust. The epicentre is the point on the Earth’s surface directly above the focus.

Why do earthquakes occur? Seismic energy is usually caused by the brittle failure (fracturing) of rocks under stress. This commonly occurs due to movement along tectonic plate boundaries Figure showing the distribution of earthquakes around the globe

Earthquake Magnitude MagnitudeEarthquake EffectsApprox. number each year < 2.5 Usually not felt, but recorded 900, Often felt, only minor damage 30, Slight damage to buildings and other structures May cause a lot of damage in very populated areas Major earthquake. Serious damage. 20 > 8.0 Great earthquake. Can be totally destructive near the epicentre. 1 every 5-10 years

San Francisco - Great Earthquake Magnitude

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

Earthquakes and Tsunami’s 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) ExtensionCompression Transform

How does an earthquake form a tsunami?

Tsunami Animations of the Boxing Day tsunami showing how the tsunami radiated from the entire length of the 1,600 km (994 miles) rupture. Above: Countries most effected by the tsunami

How do we mitigate the hazard from tsunamis? Monitoring process is very technology-intensive high costs for many poorer countries Building restrictions in hazard prone areas Seawall construction

Same Storm - Different Name

Cyclone Categories CategoryWind Speed (mph) Damage at Landfall Storm Surge (feet) Minimal Moderate Extensive Extreme > 155Catastrophic19+ The Saffir-Simpson Hurricane Scale

An intense tropical storm with winds exceeding 119 km/h is a hurricane.hurricane Severe Weather (cont.)

A low-pressure system is a large body of circulating air with low pressure at its center and higher pressure outside of the system.low-pressure system It has warm, moist air and generally brings stormy weather with strong winds. Pressure Systems

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

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

A high-pressure system is a large body of circulating air with high pressure at its center and lower pressure outside of the system.high-pressure system Pressure Systems

A low-pressure system is a large body of circulating air with low pressure at its center and higher pressure outside of the system.low-pressure system Pressure Systems (cont.)

A tornado is a violent, whirling column of air in contact with the ground.tornado Tornadoes form when thunderstorm updrafts begin to rotate. Tornado Alley is the name given to the area of the central United States that experiences the most tornadoes. Severe Weather (cont.)