Millions of Americans are at risk from man-made earthquakes

Activities such as oil and gas extraction have increased the number of man-made quakes

Six states - Oklahoma, Kansas, Texas, Colorado, New Mexico, and Arkansas - are particularly vulnerable (AP)

It has long been known that there are parts of the US vulnerable to the vagaries and dangers of natural earthquakes and tremors.

But scientists have revealed for the first time that anywhere up to seven million people may be vulnerable to the threat of manmade earthquake, created by human activity such as wastewater disposal from gas production.

The US Geological Survey has published an earthquake hazard map pinpointing potential sites of both man-made and naturally occurring earthquakes.

(USGS (USGS)

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

“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.”

The USGS reported that almost all the risk of increasing man-made quakes is tied to “companies that are injecting wastewater from gas and oil production down to porous rocks far below ground.”

The study reveals that the most significant hazard areas for “induced” or man-make quakes are located in six states - Oklahoma, Kansas, Texas, Colorado, New Mexico, and Arkansas.

Oklahoma has the highest risk, and along with Texas has the largest population that could be exposed to the risk.

“In the past five years, the USGS has documented high shaking and damage in areas of these six states, mostly from induced earthquakes,” said Mr Petersen “Furthermore, the USGS Did You Feel It? website has archived tens of thousands of reports from the public who experienced shaking in those states, including about 1,500 reports of strong shaking or damage.”

Michio Kaku, a physics professor at the City University of New York, told CBS that the number of earthquakes in those states had increased from just a handful a few years ago to more than one thousand last year.

“The injection of wastewater into the ground helps to lubricate the fault lines and expand them by over-pressurizing them, and that, we think, is causing this rash of small earthquakes,” said Mr Kaku.

Between 1973 and 2008, there was an average of 24 earthquakes with a magnitude of 3.0 or higher each year. The rate increased steadily in the relatively short amount of time between 2009 and 2015, averaging 318 earthquakes per year. This peaked just last year, with 1,010 earthquakes.