Atmosphere And Weather

What Earthquakes were the most Destructive



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Earthquakes are the most destructive natural force on the planet. They are unpredictable, striking with little warning and causing incredible amounts of damage in a matter of minutes, or even seconds. Not only can the initial tremor cause a massive loss of life, but the damage to infrastructure and the subsequent aftershocks can hamper rescue activities and promote the spread of disease, leading to further casualties.

The Richter Scale is used to measure the strength of earthquakes. Below a magnitude of 3.0 on the scale, an earthquake is unlikely to be felt. Below 5.0 will cause shaking, but is unlikely to cause damage any more serious than broken crockery. Anything above 5.0 on the scale may cause damage to building, depending on the quality of construction, and it is at this level that casualty numbers begin to rise. Over the entire planet, there are about 1000 earthquakes of this magnitude or greater every year.

However, it is the earthquakes of magnitude 7.0 and greater which make the news. About 20 earthquakes a year fit into this category and their impact is very much dependent on location. Magnitude 7.0 to 8.0 quakes which hit urban areas cause considerably more harm than rural or underwater quakes. Beyond this, in the 8.0 to 9.5 quakes are those where destruction and huge loss of life is almost inevitable. That said, of the top 10 deadliest earthquakes, only two were recorded or estimated as having magnitude of over 8.0 on the Richter Scale, demonstrating that location and local construction are more important factors than the size of the quake.

The Richter Scale was only devised in 1935, so prior to this the magnitude of earthquakes can only be estimated. Casualties are easier to estimate, even for quite old events, as historians have recorded the impact of ‘acts of gods’ since man first began to write. Nevertheless, we can only speculate on which earthquakes which greatest before the 19th century.

The most destructive earthquake in human history is believed to have occurred in China in 1556. A quake of estimated magnitude 8.0 hit the area near the city of Xi’an, in the heart of the country. The quake demolished settlemens in a radius of 250 miles. Documents from the time claim that some towns were left without a single wall standing. The city at the epicentre, Huaxian lost over 60 percent of its population - a number in the tens of thousands. In total, over 800,000 people were identified as dead or missing. Many more must have remained uncounted as entire families were lost.

China suffered again in 1976, when an quake hit Tangshan on the eastern coast. Official figures say that the death toll was 255,000, already making it the second most deadly quake in history. Estimates say the uncounted dead may have been as many as 400,000 on top of this figure. This figure may have been magnified by the attitude of the Chinese government at the time. The communist Cultural Revolution was ten years old, and Chinese authorities were extremely wary of any western influence. Offers of aid from the United Nations were refused, and the disaster was dealt with entirely internally. Tangshan was rebuilt, and now has a population of over three million people, making it one of modern China’s success stories.

In the last ten years there have been two earthquake which have caused massive loss of life. A quake on Boxing Day, 2004, neat Sumatra’s west coast, measured 9.1 on the Richter Scale, making it the third largest earthquake ever recorded accurately. The quake itself caused little damage as it was a long way out to sea. However, the tsunami that ensued hit the coastlines of numerous countries around the Indian Ocean. Some waves hit with a height of 30 metres. It is estimated that 230,000 people were killed by the tsunami and the diseases that followed. Two thirds of these were in Indonesia. Although only ten percent of this number were killed in distant India, over 600,000 lost their homes.

In 2010, a magnitude 7.0 earthquake hit the mainland of Haiti. Although not one of the strongest quakes of recent history, the devastation caused was incalculable. The epicentre was only 16 miles from the capital, Port-au-Prince, and aftershocks carried on for two weeks after the main quake, causing further harm to a shattered population. With over 300,000 killed, and one million homeless - ten percent of the country’s population - this is one of the greatest tragedies to befall a single country in all history. A year on from the earthquake, little progress has been made on the reconstruction of the country. Although the ‘international community’ provided aid in the early stages of the disaster, UNESCO has stated that Haiti appears to have been abandoned by the rest of the world.

The two greatest earthquakes of the last hundred years occurred in Alaska in 1964, and Chile in 1960. Despite the size of the quake, measuring 9.2 and 9.5 respectively, loss of life was significantly lower than other recent quakes. Six thousand were killed by the Chile quake - a terrible number, but much lower than other recent quakes. The earthquake occurred in a reasonably remote area, and local inhabitants were aware of regional seismic activity and constructed their buildings accordingly.

Because the Alaska quake was so remote, only 131 were killed, and only nine of those in the earthquake itself. Like the Sumatra quake, the majority were killed by subsequent tsunamis. The Alaska quake is the most powerful in North America in recorded history.

The majority of the most serious earthquakes, both in terms of magnitude and destruction, occur in Asia and the Americas. However, Europe also gets occasional quakes, and the most devastating hit Portugal in 1755. Lisbon was almost entirely demolished by the quake, and the total death toll in Portugal and Morocco may have been as high as 100,000. This quake was historically important as it prompted the beginning of the science of seismology, as authorities began to ask survey questions about warning signs, the propagation of the quake, and the patterns of damage.

Earthquakes are not a phenomenon that mankind will ever be able to control. All that can be done is to construct cities in such a way as to reduce the impact of the quakes, and to ensure that in risk areas there is sufficient infrastructure to cope with disasters of this magnitude. Unfortunately, it is a geological and sociological truth that the countries in the most dangerous areas - around fault lines and tectonic boundaries, also tend to be poorer. While this trend exists, further mass-destruction is inevitable. An epic quake - over 10.0 on the Richter Scale - has never been recorded, but should one hit a populated area, casualties of over a million are possible.


Sources:

http://earthquake.usgs.gov/earthquakes/eqarchives/year/eqstats.php

http://earthquake.usgs.gov/earthquakes/world/most_destructive.php

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