The ongoing rumblings of human-produced earthquakes in the southern plains of the United States may not go away anytime soon — and the odds of a costly, damaging shake may be higher than ever.

The US Geological Survey put that risk in graphic terms last week, including the risks of earthquakes linked to the injection of wastewater from oil and gas wells in a seismic hazard map for the first time. The new map places 7 million people in an area of elevated risk for a damaging earthquake, putting Oklahoma City and Dallas in the same statistical ballpark as most of California for the next year.

"If it were me or my family, I would do some of the things that people in California have been doing for a long time," said Abbie Liel, a structural engineer who teaches at the University of Colorado. That includes bolting bookshelves to walls, securing wall-mounted televisions and protecting valuable glassware or other breakables.

Liel is the principal investigator on a newly launched study of the effects of frequent, small earthquakes on buildings and infrastructure. She said the tremors that have been rattling north-central Oklahoma and parts of Texas, Arkansas, Kansas, and Colorado in recent years have "the potential for significant financial impacts."

The elevated risk isn't a big surprise in Oklahoma, where seismographs have recorded 250 earthquakes larger than magnitude 3.0 — and one as big as 5.1 — since the start of the year. Before 2009, the state had two or three small quakes a year; in 2015, it recorded more than 900. The small town of Crescent, one of last summer's seismic hot spots, was jolted last week by a 4.2 that dozens of people reported feeling in Oklahoma City and Tulsa.

The maps help illustrate how much that risk has gone up, and in which places — something the people trying to manage the problem say will help the public understand what's happening.

"The map now gives us something visual that we can show people," said Franklin Barnes, the emergency management chief for Oklahoma City. "They can look at where they live, and look at those colors, and look at the risk and intensity, and say, 'Oh, okay, I could experience a damaging earthquake. Something could happen to me because of an earthquake.'"

Scientists say the surge in seismicity since 2009 is the result of salty wastewater from oil and gas wells being pumped deep underground. Wells in the area produce 10 gallons or more of the briny waste for every gallon of oil — and the hydraulic fracturing boom that let drillers tap into previously inaccessible pockets of petroleum resulted in hundreds of millions of gallons more wastewater.

That water is disposed of in injection wells that sometimes reach more than a mile underground, where the fluid lubricates long-dormant and sometimes previously unknown faults.

The biggest shake linked to wastewater injection so far was a magnitude-5.6 earthquake that struck the town of Prague, about 50 miles east of Oklahoma City, in 2011. But scientists say a big quake is possible given the fault lines that lie beneath the prairie, and large numbers of smaller quakes raise the odds of a bigger one.

"I don't want people thinking their houses are going to fall down tomorrow," said Mark Petersen, the head of the US Geological Survey's risk mapping project. "But I do think we need to make sure that people understand they could have cracking. That affects people's houses, and they have a lot of finances tied up in their houses."

There's also a smaller chance of a quake that could cause more extensive damage—a prospect "that should be considered in planning scenarios," Petersen said. But the new map was drawn only for 2016, and policy changes might reduce the risks next year, he said.

'It's not a Hollywood version of the apocalypse.'

There have already been at least three lawsuits filed in Oklahoma over earthquake damage. The state is encouraging homeowners to add earthquake coverage to their insurance, which can cost anywhere from $50 to $300 a year, according to the state Insurance Department.

A tabletop simulation of a magnitude 6.8 earthquake in Oklahoma City projected that as many as 2,000 families would be left homeless, Barnes said. Much of the city of nearly 600,000 would be without power, water, and sewer service, and freeway interchanges would likely be undermined and impassable, snarling transportation. Oil and gas pipelines and storage tanks could be ruptured, creating hazardous material spills that would need to be contained and cleaned up.

But Oklahoma has a lot of experience with major disasters, from tornadoes that kill dozens to the 1995 bombing that destroyed the city's federal building and killed 168 people. Building codes are written with tornadoes in mind, and structures aren't likely to "pancake" like they often do in countries with less-stringent standards, Barnes said.

"The number of families that would be displaced, put out of their homes because of damage, was about the same and only a little bit greater than what we see in our largest tornadoes," he said, adding, "It's not a Hollywood version of the apocalypse."

Oklahoma's Department of Transportation reported last week that its bridges and other infrastructure aren't likely to be hurt by quakes smaller than magnitude 4.6 — a size that's still rare. Engineers will inspect nearby bridges after any quake larger than that, with the area under scrutiny determined by the size of the tremor, the department said.

It had been conducting inspections after every quake larger than a 3.0. "This change in protocol allows the department to better focus its resources," Casey Shell, the department's chief engineer, said in a written statement.

Earthquakes started to rattle the Dallas-Forth Worth area in late 2014. Authorities there are still studying the problem and expect to use the new maps in a public preparedness campaign, said Kevin Oden, the assistant emergency coordinator for the city of Dallas.

"We had just gotten off Ebola, and then this started," Oden said. "We were thinking, 'What else could come our way? What have we gotten ourselves into?'"

Oil regulators in Oklahoma, where most of the quakes are happening, have responded by demanding that operators to reduce the amount of water they're injecting, reduce the depth of their wells, or sometimes shut them down completely. In March, the Oklahoma Corporation Commission — which oversees the industry — told operators to cut back injection volumes by 40 percent over 2014 levels, a step that's being phased in through May.

The new maps are "one more piece of data" the agency can use to support its directives, which aren't mandatory, OCC spokesman Matt Skinner said.