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Figure 1- County of Kent, England in right-hand corner
Background Information



Kent is a county in southeast England, located in between the Strait of Dover on the south and southeast and the Thames estuary on the north (figure 1). Kent is one of the oldest and most historical counties in England with many famous castles and cathedrals including the Canterbury Cathedral (figure 2), which the famous English author Geoffrey Chaucer used as inspiration to write The Canterbury Tales. (1)
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Figure 2- Canterbury Cathedral
With its rich history and historic sites, tourism is a primary industry in Kent. Other industries include light manufacturing, petrolium refining, agriculture, and fishing. In addition to the historic sites in Kent, many of the residential areas within the cities are composed of simlilar architectural form, which is brick and masonry. (2)


The Disaster


On April 28, 2007 at approximately 7:18 an earthquake hit the lower region of Kent. The magnitude was recorded at a level of 4.3 on the Richter scale. (3) A seismograph of the quake can be seen in figure 3.
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Figure 3- Seismograph of Kent Quake.
The epicenter of the quake was 7.5 miles off the Dover coast nearest to the city of Folkestone (figure 4). (3,4)
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Figure 4- Epicenter of Kent Quake
The earthquake was felt in counties as far as Essex, East Sussex and Suffolk and also in Calais, which is in France. (5) The 4.3 quake was the largest recorded earthquake in Britain since 2002 where a 4.7 magnitude earth quake shook up the area in the city of Dudley, which is near the center of the Britsh Isle. (3) Previous seismic activity recorded in Great Britain are as follows: M3.5 near Dumfries and Galloway in December 2006, M5.0 near Dudley in September 2002, M4.1 near Melton Mowbray in October 2001, M4.2 near Warwick in September 2000, M5.1 April 1990 near Shropshire, M5.4 near Nefyn in July 1984, and M6.1 near Great Yarmouth in June 1931.The Kent Quake was highly random and there are no connections between previous earthquakes other than two smaller 3.5 quakes that occurred months before the Kent quake.
The damage caused by the Kent quake was more extensive than what is normally associated with a 4.0 magnitude quake. There was no loss of life and of the several injuries, many were minor; one woman was taken to the hospital with a more serious neck injury. (3) Most of the damage occurred to people's houses. According to BBC News, 474 homes were reported damaged as a result of this earthquake. After inspection 73 of those homes were declared uninhabitable. While a 4.0 level earthquake does not cause extensive shaking, more damage was caused in the Kent incident due to the architecture of the buildings. Many of the structures in Kent are older and are composed of brick and cement. Many chimneys fell over and outer bricks were shaken loose from walls and toppled onto cars. (figures 5 and 6) (3)
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Figure 5- Police help an older woman to safety
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Figure 6- Car damaged by dislodged bricks
Thousands of homes were left without power for several hours and the Salvation Army stepped in to provide temporary shelter to 100 people whose houses had been damaged to an extent that they were unable to be lived in. (3) While many homes and other buildings were damaged bringing a cost estimated at tens of millions of dollars, the major infrastructure such as roads and highways remained undamaged. (3) Emergency services were thus unhindered and were able to provide immediate assistance to those in need. The damage caused by the Kent quake occurred primarily on a local scale, but there was at least one major reaction that took place further away. Following the Kent quake a huge crack appeared in a cliff near New Forest in
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Figure 7- Crack in cliff in Hampshire
the county of Hampshire. (figure 7) It is still not quite certain if the quake in Kent caused the crack "but it is too coincidental to ignore." (MCA spokeswoman) (3) The crack is feared to have the potential to cause a major landslide which would damage expensive real estate below. (3) Another small earthquake has the potential to cause the landslide. So for a relatively small 4.3 earthquake, the Kent quake caused extensive damage in the immediate area and beyond.







Comparison to 4.3 Quakes in California

As previously seen, the 4.3 earthquake in Kent caused substantial damage to the area. If the same magnitude quake occurred in California the damage would be far less than that in Kent. Most of the damage in Kent, England was structural (figures 5 and 6) with bricks loosening and falling on top of cars. The building codes in California are far more strict than they are in England, whose buildings consist of brick and masonry and are susceptible to damage from even minor earthquakes unlike buildings in California.
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Figure 8-Map of 4.3 quake near Watsonville
In 2007 a 4.3 magnitude earthquake occurred near Watsonville in Northern California (figure 8). The quake was felt throughout the region, but there were no injuries and the damage was limited to "a few items falling off store shelves." (8) This was the same magnitude quake that occurred in Kent, England and yet as compared to California, the only damage was a few things falling off of shelves. Thanks to stricter building codes, Californians are less susceptible to damage caused by smaller earthquakes and earthquakes in general.


Compare building structure:
California
was the birthplace of seismic system for buildings in the United stated. After the earthquake in 1906, many scientist and engineers come together and concluded that wooden buildings could withstand an earthquake better than concrete or masonry based on their review of the damage. The wooden need to secure to their foundations and incorporated with appropriate internal bracing. California buildings are built to stand in a small earthquake. Therefore, California building can resist earthquake better than county of Kent in England because the county of Kent in England was build to last but was not build to stand to resist earthquake. Many building were unreinforced masonry structures, on the other hand, could stand better in earthquake if the handful of reinforced concrete structures had done to the best, in presence with somewhat little structural damage. Concrete is strong in compression, as the aggregate capably carries the compression load, but it is weak in tension as the cement holding that aggregate in place can easily crack during the earthquake, allowing the structure to fail. The Reinforced solves these problems by adding steel or metal reinforcing bar to carry tensile loads.



Sources
1. http://www.visitkent.co.uk
2. showcase.netins.net/web/pullen/img/England.jpg
3. http://news.bbc.co.uk
4. http://neic.usgs.gov/neis/bulletin/neicbsalw.html
5. http://www.emsc-csem.org
6. http://www.earthquakes.bgs.ac.uk/helicorder/heli.html
7. http://neic.usgs.gov/neis/bulletin/neic_bsal_w.html
8. http://alpineequakes.blogspot.com/2007/07/43-quake-felt-near-watsonville.html