The U.S. Geological Survey (USGS) recently published a report saying that millions of American lives are in danger due to human-induced earthquakes.

According to the USGS report, about 7 million Americans who work and live in Central and Eastern U.S. are at risk of man-made earthquakes that can cause damage similar to natural earthquakes usually felt in California.

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

From highest to lowest impact, the states that face significant hazards from man-made earthquakes are Oklahoma, Kansas, Texas, Colorado, New Mexico and Arkansas.

Oklahoma and Texas have the highest populations that may be affected by these seismic activities.

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

Induced earthquakes are triggered by human activities, such as hydraulic fracturing or fracking.

Fracking, according to BBC, is an industrial process of extracting fossil fuel, such as oil and methane gas, seated deep underground by breaking apart rock formations.

After a well is drilled, huge quantity of fresh water mixed with fracking fluids is injected in the hole. This high pressure mixture then fractures the rock.

Stanford reported that the mixture being used in fracking can contain potentially dangerous chemicals, such as benzene and xylene.

Aside from human-induced earthquakes, fracking also poses several hazardous issues.

According to the study published in Environmental Science and Technology, fracking operations near Pavillion, Wyoming, have affected the underground sources of drinking water.

Fracking can also contribute to air pollution and climate change. Methane, a main component of natural gas, can leak during the drilling and transport process.

According to Greenpeace, methane gas--a less common but more potent greenhouse gas than carbon dioxide--is 85 to 100 times more powerful than carbon dioxide in unsettling the climate over a 20 year period.