(NaturalNews) According to the most recent federal earthquake map from the U.S. Geologic Survey (USGS), roughly half of the United States is at a higher risk of quakes than previously thought.

The actual risk is probably even higher, as the map does not take into account increased risk due to oil and gas extraction techniques such as hydraulic fracturing ("fracking") and carbon dioxide injection.

The federal report, published July 17, is the first update to the earthquake map since 2008. It takes into account new advances in data analysis, modeling technology and sensing instruments, and includes data gathered from the 2011 earthquakes in Virginia and Japan.

Many states unprepared

The USGS identified 16 states that are at the highest risk of earthquakes: Alaska, Arkansas, California, Hawaii, Idaho, Illinois, Kentucky, Missouri, Montana, Nevada, Oregon, South Carolina, Tennessee, Utah, Washington and Wyoming. The addition of South Carolina is notable, as that state has not experienced a large earthquake since 1886.

Yet, according to the new analysis, 42 states have a "reasonable chance" of experiencing a significant quake within the next 50 years. This includes many states that do not plan for earthquakes, assuming that their risk is low.

Many of those states have actually experienced major earthquakes in the past, but long enough ago that people today tend to regard them as anomalies. For example, the 1886 South Carolina quake killed 83 people in Charleston alone, while a 1775 earthquake centered on Cape Ann, Mass. caused major damage to Boston and was felt as far away as Nova Scotia in the north and Chesapeake Bay in the south.

Similarly, the last significant earthquake in the Central Virginia Seismic Zone prior to August 2011 took place in 1875.

"People tend forget about these quakes," said Mark Petersen, chief of the USGS National Seismic Hazard Mapping Project.

"It's important that people consider the hazard that they face. This might be low on the list of priorities for some places, but it's important when the consequences of inaction are very high."

Oil and gas drilling increases risk further

In regions of the country with oil and gas drilling, the risk is likely even higher than the report indicates, as the USGS analysis did not include any of the new data linking fossil fuel extraction to increased quake risk.

As oil and gas becomes harder to obtain, the industry is increasingly turning to techniques that require injecting fluids underground. Carbon dioxide injection, for example, boosts the production of aging wells, while fracking uses water to break apart subterranean rocks and ease access to oil and gas. The water used in fracking becomes contaminated in the process and is then typically disposed of via injection back underground at a separate location.

All of these practices increase pressure on underground faults, and studies suggest that they have contributed to a recent spate of earthquakes in Texas and Oklahoma. For example, a study by researchers from Cornell University published in the journal Science on July 3 found that wastewater injection wells could trigger quakes up to 30 miles away and that their range of influence is increasing as more fluid continues to be injected. The researchers believe that, as more fluid is injected, the quakes will also increase in magnitude.

USGS data show that, between 1967 and 2000, there were an average of 21 earthquakes per year above magnitude 3.0. Between 2010 and 2012, that number jumped to 100. Almost all these quakes took place in states with wastewater injection. Oklahoma alone has accounted for almost half of the seismic activity in the central and eastern United States since 2008.

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