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 You wake in the darkness, unsure about what has disturbed you. Strangely, the clock on your bedside table begins to rattle about, as if it has a will of its own. You become aware of a strange roaring sound outside, like a jet passing overhead. The rattling grows and strengthens. Suddenly, the earth moves, bucking like a wild animal. Your room heaves; glasses crash in the kitchen; paintings fall from the walls. What is it? What could make the normally stable earth move like this? Throughout human history there have been many attempts to explain earthquakes from a disturbance created by growling demons who live beneath the earth to the movements of the giant tortoise who carries the world on his back. Over time, other ideas were proffered: perhaps these shakings were the result of great subterranean explosions, or the collapse of huge underground caverns. While all of these explanations had an element of plausibility, none seemed to explain the strange distribution of earthquakes around the world. Some regions, such as California and Japan, have always had far more earthquakes than others, while some parts of the world, such as Sweden and Australia, almost never have any.
When Plates Collide
Have you ever looked at a map of the world and noticed that Africa and South America look like puzzle pieces that could fit together? Scientists had long wondered about this. In 1912, Alfred Wegener, a German scientist and adventurer, proposed the idea that the continents had once been part of a huge
super-continent that he called Pangaea. Wegener proposed that, over a time span of 200 million years, Pangaea had broken apart and the individual pieces had somehow changed position. Reactions to Wegener's theory ranged from curiosity to scorn, since no one had any idea how continents might move. Finally, 25 years after Wegener's death in 1930, scientists mapping the ocean floor discovered a huge undersea mountain range. It extended for over 40,000 miles, running north to south along the middle of the Atlantic Ocean and wrapping around the tip of Africa and beyond.
Down the center of this range, from end to end, a deep trench appeared. This trench, called the "global rift," turned out to be a site where magma--hot molten rock--was welling up from inside the earth, and then cooling in the ocean waters to form a new rock. The new, cold rock was being pulled downward by gravity, dragging the land along behind it. Scientists had found the engine for the movement of the continents, called continental drift. The earth's inner core is a solid ball of nickel and iron surrounded by an outer core of molten metal. Beyond that is an area of rock called the mantle. In the early part of earth's existence, hot rock cooled to form the earth's surface, or lithosphere. The coolest, most brittle upper section of the lithosphere is called the crust.
Over the eons, the earth's lithosphere has cracked, creating seven large, and over a dozen smaller, huge stone slabs called plates, which may be up to 100 km thick. These plates, which float like islands on the mantle, get pulled around by the cold plates as they sink. The points at which these plates meet one another -- called faults, or fault lines -- are areas of intensified seismic and volcanic activity. These junctures are not peaceful places. Imagine two trucks colliding. In this case, however, each "truck" is the size of a continent, and the whole event is happening in extreme slow motion. In these massive collisions, the plates can act in three different ways: they can smash into each other, crumpling up to form mountains; they can slide past each other, sometimes triggering earthquakes; or one can dive beneath the other, in which case part of a descending plate can melt and rise up to form a volcano.
Environmental losses
 The location of the disaster will affect resultant costs. Thus, a major Atlantic quake striking a broad swathe of the west cost of the United States where there are some significant concentrations of wealth (perhaps involving minimal if any fatalities) might prove significantly more costly than a disaster involving significant loss of life and property damage in another region. With populations becoming increasingly concentrated, there is a growing need "to be prepared". As the Secretary General of the United Nations observed, "We must, above all, shift from a culture of reaction to a culture of prevention. Prevention is not only more humane than cure; it is often cheaper. Above all, let us not forget that disaster prevention is a moral imperative". A number of measures may be employed - these might include developing public awareness of basic disaster prevention techniques, developing risk reduction and/or monitoring strategies/capabilities, international co-operation - all will play their part. Perhaps above all, however, the availability of adequate resources, both in terms of expertise and finance, must be the priority and in many cases, particularly in the so-called developing world, this may not always be immediately possible - hence the very real need for international co-operation.
 Since January 1987 there have been a number of natural catastrophe insured losses totalling US$1 billion and above. That being said, it is important to stress that overall financial losses (physical damage costs, loss of business production, etc.) resulting from an individual event, are often significantly higher than the overall insured loss. For example, estimates of losses resulting from the mid August 1999 Turkish earthquake (per the World Bank) exceed US$10 billion although insured losses are expected to fall short of US$1 billion at perhaps US$750 million or so (contrary to some early published projections). Damage resulting from the September 1999 earthquake that caused substantial damage in Athens, has been estimated at around US$1.5 billion (insured losses fall below US$1 billion). According to the Venezuelan authorities, overall damage costs resulting from the mid December 1999 Venezuelan flooding/landslides varied between US$10 and US$30 billion! As at mid March 2000, compensation claims resulting from the September 1999 accident at the Tokaimura Fuel Conversion Plant in Japan, were projected to approach US$100 million.
Source: The Exploratorium
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