7m Americans At Risk From Man-Made Earthquakes

Seven million Americans live and work in areas in central and the eastern US vulnerable to man-made earthquakes, according to a new report.

The US Geological Survey (USGS) has published an earthquake hazard mapwhich pinpoints potential sites where damage could occur from both natural and induced quakes in 2016.

It shows that some parts of the central and eastern US have a similar chance of the kind of damage that high-risk areas in California get from natural earthquakes.

Mark Petersen, chief of the USGS National Seismic Hazard Mapping Project, said: "By including human-induced events, our assessment of earthquake hazards has significantly increased in parts of the US.

This map shows where earthquakes have taken place since 1980

"This research also shows that much more of the nation faces a significant chance of having damaging earthquakes over the next year, whether natural or human-induced."

Man-made or induced earthquakes are triggered by human activity, with the disposal of waste water the primary cause.

Waste water from oil and gas production operations can be disposed of by injecting it into deep underground wells, the report states.

The six states which face the highest chance of damage are Oklahoma, Kansas, Texas, Colorado, New Mexico and Arkansas.

Both Oklahoma and Texas have the largest populations exposed to induced earthquakes.

Mr Petersen said: "In the past five years, the USGS has documented high shaking and damage in areas of these six states, mostly from induced earthquakes.

The report estimates where, how often and how strong ground shaking could be in the US during 2016.

It reveals that there has been a dramatic increase in seismic activity in the central US in the last six years.

From 1973 to 2008, there were an average of 24 earthquakes at magnitude 3.0 or higher per year. Between 2009 and 2015 that rate steadily increased, with an average of 318 per year and a peak of 1,010 in 2015.

So far this year, there have been 226 earthquakes of magnitude 3.0 or larger in the central US.

The report states: "Wastewater disposal is thought to be the primary reason for the recent increase in earthquakes in the CEUS (Central US).

"While most injection wells are not associated with earthquakes, some other wells have been implicated in published scientific studies, and many states are now regulating wastewater injection in order to limit earthquake hazards."

The report adds that concerns have been raised about hydraulic fracturing - known as "fracking" - but that USGS studies suggest it is only rarely behind earthquakes.