Biggest Earthquake to hit Virginia in 110 Years - 5.8
2011 08 23

From: dailymail.co.uk



The 5.8-magnitude earthquake that struck in Virginia and was felt in New York and Washington D.C. today was a rare event for the east coast.

But the shaking was believed to be so widespread because the tremors of the quake were shallow at between one and four miles deep.

It’s the strongest quake to hit the Virginia area since 1897 - and resulted in buildings such as the Capitol and Pentagon being evacuated.

The quake’s severity was ’highly unusual’, one Brown University professor said, although it was in an area known for smaller quakes and it spread because of accommodating terrain.

’This is the largest earthquake by far that I am aware of occurring there in recent history,’ seismology professor Karen Fisher said.

The wide spread of the shockwaves was common for the east coast - which is largely due to the difference in the terrain, research seismologist Peggy Hellweg said in California.

’(California’s) ground is all of this chopped-up stuff - like a pile of marbles,’ she said, which means that the waves from a quake don’t spread out that far.

But in eastern America, ’what you’ve got there is gorgeous bedrock (and) the waves propagate beautifully.’

In addition, there is a difference in plate tectonics because the west coast is over the boundary between the North American and the Pacific.

She said in the East, ’There’s no driving engine in terms of the two plates sliding past each other - so that’s why it’s much more unusual.’



Small earthquakes have been happening in central Virginia since at least the 1770s, reported the U.S. Geological Survey.

Quakes in central and eastern parts of the U.S. are less frequent than those in the west but are normally felt over a larger region.

Earthquakes east of the Rocky Mountains can be felt over an area up to ten times larger than one of a similar strength in the west.

An earthquake of the 5.5 level can often be felt as far as 300 miles from where it happened and cause damaged up to 25 miles away.

Quakes happen on faults within bedrock that are usually miles deep, reported the U.S. Geological Survey.

Bedrock beneath Virginia came together as continents collided to create a super-continent up to 500 million years ago.

This was what raised the Appalachian Mountains and the bedrock rifted apart to form northeastern America and Europe.

The nearest plate boundaries from the central Virginia seismic zone are in the centre of the Atlantic Ocean and Caribbean Sea.

But few shakes in the seismic zone can be connected to named faults because many are deeply buried and undetected.

Therefore the best guide to earthquake hazards in this seismic zone is actually the earthquakes themselves.

’There’ll be an earthquake in New York soon,’ seismologist said in February

A top seismologist warned in February that New York City was due for a big earthquake, following the last big shake of 5.3 in 1884.

Won-Young Kim, of the Lamont-Doherty Earth Observatory at Columbia University, said the city gets a big quake around every 100 years.

Magnitude 5 earthquakes would not be expected to take down buildings, but could damage brick buildings and chimneys, scientists predicted.

Seismologist John Armbruster told Metro New York in February that a big earthquake could result in ’billions in damage’ and even deaths.

Virginia’s 5.9 shake of 1897 and others

The largest earthquake to originate in Virginia in recent times was a 5.9 in May 1897, with the epicentre in Giles County.

An earlier tremor four weeks before had already caused damage in the area.

The shock was felt in Georgia, Pennsylvania and in Indiana and Kentucky - covering an area of around 725,000 sq km.

Virginia has suffered more than 160 earthquakes in 30 years - but only a sixth were actually felt.

The largest damaging earthquake in the seismic zone was a 4.8 in 1875. The biggest was 5.9 in 1897, reported the Richmond Times-Dispatch.

Last October a 2.4 hit near Ashland and a 2.4 struck north of Richmond, but there were no injuries or damages.

Source: dailymail.co.uk




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