Earthquakes • Group: • Tanner • Marco • Antonio • Ramón • Felipe
What are earthquakes? • One of the most frightening and destructive phenomena of nature is a severe earthquake and its terrible aftereffects. An earthquake is a sudden movement of the Earth, caused by the abrupt release of strain that has accumulated over a long time. For hundreds of millions of years, the forces of plate tectonics have shaped the Earth as the huge plates that form the Earth's surface slowly move over, under, and past each other. Sometimes the movement is gradual. At other times, the plates are locked together, unable to release the accumulating energy. When the accumulated energy grows strong enough, the plates break free. If the earthquake occurs in a populated area, it may cause many deaths and injuries and extensive property damage.
Where do earthquakes occur most often?? • Although it's possible for earthquakes to occur in any area of the world, seismologists have concluded that most quakes are seen and felt in three specific areas: • Pacific Seismic Belt:This area is found around the outer edges of the Pacific ocean. Nearly 80-percent of all large quakes occur in this region. The Pacific seismic belt measures from Chili to South America to the western region of the United States, including the southern tip of Alaska, the Aleutian Islands, Japan, New Guinea and New Zealand. • Alpide:The Himalayas, Mediterranean and the Atlantic make up the Alpide belt region. Approximately 18-percent of all earthquakes occur in this area. • Mid - Atlantic Ridge:The mid-atlantic ridge is the third most likely area where quakes occur, and covers the region of from the north-south axis of the Atlantic to the Arctic Ocean to the southern-most tip of Africa. • In the United States, Alaska and California see more earthquakes each year than any other State. Florida and North Dakota are rarely affected by quakes.
How likley is it your area experience an earthquake?? • There have been many earthquakes in Peru. The first one we remember is the one in 1966. Buildings and schools were crumbled. But some students were lucky because they were not in school that day. In May 31,1970, Mount Huascaran, Peru, a terrible magnitude 7.8 earthquake-induced rock and snow avalanche on Mt. Huascaran, buried the towns of Yungay and Ranrahirca. The total death toll was 66,794. The avalanche started as a sliding mass of glacial ice and rock about 3,000 feet wide and one mile long. The avalanche swept about 11 miles to the village of Yungay at an average speed of more than 100 miles an hour. The fast-moving mass picked up glacial deposits and by the time it reached Yungay, it is estimated to have consisted of about 80 million cubic yards of water, mud, and rocks. More than 60 countries responded with emergency relief. The last earthquake in the past feature was in October 3,1974 in Lima, Peru. Over 2,000 were injured, and a column failure caused the roof to sag on a one-story classroom at Agricultural University.
Emergency response plan • Following a major earthquake in southern California some years ago, one of the seismological laboratories there decided to investigate the expected aftershock sequence. They got permission to establish an array of seismometers on a large ranch near where the earthquake had occurred. The seismologists set up the array which fed signals by wires into a large, wrist-sized cable that led into a portable recording van. • They soon got everything working, and signals were humming into the van to show the occurrence of many small aftershocks and some large enough to be felt. Then, suddenly, all the signals ceased. Seeking the cause of the termination, the seismologists went outside the van to find a woman standing with axe in hand beside the seismograph cable which she had just chopped neatly in twain. Defiantly, she explained "we've had enough earthquakes around here lately without you guys making any more." • A similar approach to the problem has been reported by California seismologist Bruce Bolt. In his book Earthquakes? A Primer, he tells of a handyman at the seismographic station in the Bahamas. During a strong earthquake in 1965, the man drew out his pistol and shot the jittering seismograph in an attempt to quell the violent ground motion.