Approximately 3.5 million people live and work in areas of central and eastern USA with significant chance of damage from a human-induced quake in 2017, the USGS stated.
The USGS down-scaled the chances from its 2016 forecast.
The seismic risk is forecast to be so high that the chance of damage in Oklahoma and southern Kansas is expected to be similar to that of natural earthquakes in California, USGS scientists writing in the journal Seismological Research Letters said Wednesday. That decrease led the agency to project less seismic activity in those areas for this year than it did in its 2016 report, he said.
But the report also notes that the overall seismic hazard for 2017 is lower than a year ago.
Oklahoma experienced about 2,500 earthquakes of at least 2.7 magnitude in 2014, followed by 4,000 in 2015 and 2,500 last year after experiencing an average of about two per year between 1980 and 2000, according to the report.
The number of Americans who live in areas threatened by man-made earthquakes is half of what it was a year ago, researchers said Wednesday.
"Millions still face a significant chance of experiencing damaging earthquakes, and this could increase or decrease with industry practices, which are hard to anticipate", Petersen said.
About 3.5 million people live and work in the areas of Oklahoma and southern Kansas identified as at risk of induced seismicity. Oklahoma also saw the largest quake ever recorded in the state in 2016, when a 5.8 natural disaster struck near Pawnee.
The focus there is on the hazard from natural earthquakes.
Researchers have blamed the increase in man-made quakes on the injection of wastewater from oil and gas drilling operations into the ground. USGS has connected past Oklahoma earthquakes to injection wells, concluding that the massive volumes of wastewater are changing the underground pressure, lubricating the faults and triggering earthquakes.