Natural Causes The formation of earthquakes is closely related to plate margin activity. They are the result of a slow build up of pressure along the plate boundaries. When the rocks are forced beyond endurance they break apart in a sudden release of energy, and result in the earth shakings we refer to as earthquakes. Volcanic activity may also be result in earthquake. As there is a massive amount of pressure built up within the volcano which leads to an eruption and violent tremors.
Human Causes Man has a way of affecting nature, and so causing his own difficulties. Coal mining: When mining coal, sometimes miners have to pump out water as well as the coal. With the large amounts of coal being mined everyday due to demand, there has been a major shift in the mass of the region. As such there is increased stress on the remaining rocks, making earthquakes more likely to occur.
The construction of high rise buildings: These building may weigh more than 700,000 metric tonnes. This weight upon a comparatively smaller surface area will lead to excess pressure being exerted on the earth’s crust under these structures. Building dams: The weight of the water when the valley behind the dam is filled causes increase pressure on the earth crust. Resulting in earthquakes. As was the case with the Hover dam that experienced hundreds of tiny tremors all in relation to the water’s level.
Classification of earthquakes
There are four types of earthquakes: Tectonic Earthquake : They originate within the earth’s crust as a result of the plates movements in relation to each other. Also the movement of the loose fragmented rocks that make up the earth’s crust may lead to tremors. They occur most frequently, and are mostly severe and of a high magnitude. Shallow quakes are experienced at transform margins, and deeper tremors at subduction zones.
Volcanic Earthquakes : These occur in two cases either prior to or during an eruption: Prior to eruptions when volcanic vents are blocked, and an intense pressure is caused by the trapped magma, the release of this pressure as an eruption may lead to an earthquake. During and eruption magma is expelled leaving an opening. The rocks move towards this opening trying to fill it causing severe earthquakes.
Collapse Earthquakes: These are small earthquakes that are the result of pressure induced in rocks resulting in the collapse of the roof of caves, tunnels, mines, and other subterranean openings. Explosion Earthquakes: These earthquakes induced by mans activities are a side effect of the modern nuclear war. As explosions occur it causes it causes
Body waves P Waves : They are the fastest waves and as such are the first to be felt during and earthquake. They travel backwards and forwards through the earth’s crust. Moving in the same direction as the wave. Their ability to travel through both liquids and solids allows them the great speeds at which they travel up to 5000m/s. S waves : They are slower and larger than P waves, and are able to only pass through solids. They are the cause of the vertical movement of the ground. It moves the ground upwards and downwards resulting in much damage, as most building cannot support horizontal stress.
Surface waves Love waves: It’s movement is similar to that of the S waves as it has no vertical displacement. They move the ground horizontally but at right angles to the direction of propagation. They are responsible for quite a great deal of damage done to buildings. These waves cannot travel through and so may only have an effect on the sides of lakes, merely pushing the water sideways. Rayleigh waves : have similar circular characteristics as that of the waves found in the ocean. They move both horizontally and vertically. Due to this vertically components they are able to affect the movement of bodies of water such as lakes.
Effects of earthquakes
Primary Secondary Shaking and ground ruptures are the main effects of earthquakes. Landslides Collapsed buildings Gas and water lines burst Fissures in roads and sidewalks Aftershocks Fires Diseases form water contamination Blocked roads Dam disturbances Floods Tsunamis Soil liquifaction Death
Mitigation The instigation of siting, structural, and land use regulations to decrease existing risk, and prevent future risk. Retrofitting existing buildings Transferring the responsibility of the risk by getting insurance. Also educating the public and raising awareness of earthquake risks
Personal Level Before Ensuring that the building in which you live meets construction requirements to withstand earthquakes. Secure cupboard doors with latches Bolt and secure heavy objects to the floor and walls Repair and cracks as earthquakes can turn cracks into ruptures Hang heavy objects like pictures away from where people sit earthquakes can knock items off walls Place chemicals in latched low shelves. Have an earthquakes preparedness kit
During When indoors stand in doorways and crouch under desks and tables When outside stand in large open areas away from light poles, trees, and anything that may fall In an automobile drive away from bridges and stop in the safest place possible Stay Calm!
After Evacuate the building as soon as shaking stops Check for injured persons Check for safety hazards, broken gas mains, etc. Turn off utilities and do no use any open flames Keep battery operated radio and listen for updates Wear shoes and protective clothing Be prepared for aftershocks
Government level Provide a building standard for contractors to allow for sound housing. Educating the population on earthquakes as a hazard. Putting in place safety regulations such as a standard for the number of emergency exits. Providing service teams for search and rescue operations after the earthquake.
Prediction Methods and Techniques
Methods Examining historical evidence Monitoring crustal movement and volcanic activity Studying the electrical and magnetic changes in rocks Watching for unusual behaviour in animals
Developed vs. Developing countries Developing countries tend to suffer more damage than Developed countries because: The buildings in LDC’s are of a poorer quality and are more subject to collapsing during earthquakes, as building codes are not enforced Lack of resources for proper evacuation leading to a greater loss of life There is a general lack of scientific knowledge about disaster preparedness More developed countries however will have a greater cost of overall damage They will also have a smaller amount of casualties
Haiti When a 7.0 earthquake hit Haiti on January 12th,2010 it left 316 000 people dead ,250 000 injured and a further 1.5 million homeless. It was the worst earthquake to hit the region in 200 years, costing the country between $7.2- $13.2 billion. The Earthquakes left many important buildings destroyed such as the Presidential Palace and the National Assembly. The collapse of these building cost many their lives including some important names, such as the archbishop of Port-au Prince and the opposition leader Micha Gaillard.
U.S.A. San Francisco On the 18th of April 1906 a great earthquake shook san Francisco at 5:12 AM.Though there is some speculation around the magnitude it is believed to be roughly 7.9.The earthquake was felt from southern Oregon to south of Los Angeles and inland as far as central Nevada. It is quoted that the estimated death toll neared 3000 people in the San Francisco area with 189 deaths being reported elsewhere, and hundreds of thousands of people left homeless.
Chile An 8.8 magnitude hit Chile on the 27th February ,2010. It was felt strongly in six Chilean regions (from Valparaisointhe north to Araucania in the south), that together make up 80 percent of the country's population. Hundreds of people were reported dead and a further 1.5 million homeless. The earthquake is tied for the fifth largest earthquake since the 1900’s, and set in motion a tsunami wave that ravaged near by islands.