23 October 2013 18:08 [Source: ICIS news]
WASHINGTON (ICIS)--The number of earthquakes in central Oklahoma has increased 13-fold in five years, the US Geological Survey (USGS) said on Wednesday, adding that the quake “swarm” may be related to oil and gas drilling in the area.
In the results of monitoring done in cooperation with the Oklahoma Geological Survey (OGS), USGS said that there have been more than 200 magnitude 3.0 or greater earthquakes in central Oklahoma since January 2009, “marking a significant rise in the frequency of these seismic events”.
USGS seismologist Bill Leith said that in the period from January 2009 through mid-2013, the average number of magnitude 3.0 earthquakes has climbed to 40 per year.
Prior to 2009, that central Oklahoma region typically experienced a 3.0 magnitude or higher temblor only one to three times per year in the 1975-2008 period.
Leith said that USGS is assessing the possibility that the rash of Oklahoma quakes -what geologists call an earthquake swarm - could increase chances for a large earthquake striking the region.
USGS also is “evaluating possible links between these earthquakes and wastewater disposal related to oil and gas production activities in the region”.
If the Oklahoma earthquake swarm can be definitively linked to oil and gas drilling - and the hydraulic fracturing (fracking) technique in particular - it would likely accelerate efforts being made by Washington to regulate and perhaps restrict fracking.
Fracking and horizontal drilling are key to production of newly abundant natural gas from shale deposits in a half-dozen areas across the US.
Minor earthquakes in England in April-May 2011 were attributed to a fracking operation.
An earlier study by OGS said there was a “strong correlation” between fracking and a swarm of 50 low-magnitude quakes that struck Elmore City, Oklahoma, in a 24-hour period in January 2011.
Leith said that a statistical analysis of the Oklahoma swarm “suggests that a contributing factor to the increase in earthquake triggers may be from activities such as wastewater disposal, a phenomenon known as "injection-induced seismicity”.
On the Richter scale, an earthquake of 3.0 to 3.9 magnitude is classed as “minor” and can often be felt by people and might rattle indoor objects but rarely causes any damage.
A quake in the magnitude range of 4.00 to 4.9 is considered “light” and would be clearly felt by people in the region, would cause objects to fall off shelves or fall over and might result in no or minimal structural damage.
Leith said that earthquakes of magnitude 4.2 and 4.4 struck in an area east of Oklahoma City on 16 April this year, causing objects to fall off shelves.
As part of the recent five-year swarm, a far more serious magnitude 5.6 temblor hit near Prague, Oklahoma, on 5 November 2011 and caused damage to homes and larger structures.
It was the largest quake ever recorded in Oklahoma, and the last previous earthquake in the 5.0 or higher magnitude range was in 1952.
USGS said that while Oklahoma has been known for decades to be “earthquake country”, the new swam of temblors is “an increased hazard that has important implications for residents and businesses in the area”.
At least 10 different federal agencies have already launched as many as 14 separate regulatory initiatives aimed at determining the environmental impact of fracking and whether federal regulation or restriction of the technique is needed.
Last year the White House set up a multi-agency task force to consider whether and how fracking should be regulated at the federal level. Also last year, the Environmental Protection Agency (EPA) issued rules governing emissions from fracking operations and other gas drilling.
Part of the Interior Department, USGS is focused on providing reliable scientific information to describe and understand the Earth.
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