Oklahoma has seen a dramatic rise in the number of earthquakes since 2009. Credit:bigberkeywaterfilters.com "You have to be real close to a bomb to get the concussion you get from a primary wave from an earthquake that is a quarter of a mile [400 metres] away." His wife, Ilke, agrees, and like her husband she knows what a bomb blast feels like. As a girl she survived the Allies' bombing campaign huddling in the cellars of Nuremberg. And it is not just the perceptible earthquakes – those measuring more than 3.0 on the Richter scale and above – that are bothering locals. Some fear that the next one could be "the big one". In some areas the ground seems to be constantly trembling, and earthquakes are being measured in "swarms" rather than as singular events.

A protest against fracking in Los Angeles. Credit:Reuters And the rumbling of the ground has opened fissures in communities between those who want the fracking to continue unfettered, those who want regulations improved and those who want it banned. _________ Oklahoma's state seismologist, Dr Austin Holland, took his post in 2009 and soon after he arrived he observed a swarm of earthquakes. At first he was not too concerned – he had seen the phenomenon before - but after the activity did not settle down in the coming days he began to worry. Since then the seismic activity has increased further and Holland says he does his work investigating and mapping the quakes with a palpable sense of urgency.

He confesses to having resumed smoking and upped his coffee intake to help him through the hectic workday. He is now confident that the earthquakes and the oil industry are linked, though not directly through the fracking. Two recent technical breakthroughs launched the fracking boom that has again made the US an energy superpower over the past five years. First, drillers learned to turn their bits sideways when they hit porous shale filled with formerly unrecoverable oil. Then they learned to force millions of litres of a water and chemical cocktail into the shale, breaking it open so the oil flowed freely to the top. The problem is that you then have to find somewhere to put the unusable wastewater from the fracking process. The solution in Oklahoma was to bore even more holes and to pump the wastewater into them at high pressure.

Holland believes this pressure - not the water itself - is acting as a lubricant along fault lines, though more study will be needed to work out why it is affecting Oklahoma more than other states. Asked if he shares the fears of many locals that the reinjection of wastewater could cause "the big one", he chooses his words carefully. "I don't want to sound alarmist," he begins, adding that his job includes educating the public and Oklahoma's politicians about how to prepare for such an eventuality. He notes that 1300 years ago – a blink of an eye in geological time – Oklahoma was hit by a magnitude 7 earthquake. By comparison, the 1995 Kobe earthquake of 6.9 magnitude killed more than 5000 people and caused more than $100 billion in property damage - making it the most costly earthquake in history at that time.

For a long time the industry regulator in the state, the Oklahoma Corporation Commission, a body that some accuse of being too close to the oil industry, was reluctant to recognise the link, though recently it appears to have conceded. But in a 2013 press release announcing the adoption of what it calls a "traffic light system" to increase seismic monitoring of wells near fault lines, the commission said, "While a direct, definitive link of oil, and gas activity to the current major seismic events in Oklahoma has not been established, the Oklahoma Corporation Commission is not waiting for one." Just last week the US Geological Survey made its strongest statement to date on the issue, writing in a press release that large "areas of the United States that used to experience few or no earthquakes have, in recent years, experienced a remarkable increase in earthquake activity that has caused considerable public concern as well as damage to structures. "This rise in seismic activity, especially in the central United States, is not the result of natural processes. "Instead, the increased seismicity is due to fluid injection associated with new technologies that enable the extraction of oil and gas from previously unproductive reservoirs. These modern extraction techniques result in large quantities of wastewater produced along with the oil and gas. The disposal of this wastewater by deep injection occasionally results in earthquakes that are large enough to be felt, and sometimes damaging. Deep injection of wastewater is the primary cause of the dramatic rise in detected earthquakes and the corresponding increase in seismic hazard in the central US."

The Oklahoma Corporation Commission's spokesman, Matt Skinner, told Fairfax Media this week that the traffic light system was just the first step. "This is a No. 1 critical issue ... We're not presenting this as 'Oh, don't worry we've got the answer'," he said. "When your house is shaking how can you be reassured? What's happening is a frightening thing." Of most concern to the commission, he said, were the towns of Medford and Cherokee. "They are getting absolutely hammered. The rise in seismicity and what's most concerning is the rise in the magnitude of seismicity has been stronger there than anywhere else." Medford is a speck of a town on Oklahoma's flat far northern prairie. Its grain elevator and water tower are by far the tallest structures on the plain.

The city manager, Dea Mandeville, says the oil boom has been good to the town. The drillers and fracking crews filled the local motel and spilled into new trailer parks and with the increased revenue they were able to reseal the roads, build a pool, replace the fire trucks and buy two new ambulances for the community of about 1000 people. But since the fracking finished – once the wells have been fracked the oil flows and the crews move to the next site – the revenues have slumped but the earthquakes continue. She says people are not in fear for their lives, but live in a state of constant, nagging concern. "Most people, if they're like me, are more anxious at night, because you're sound asleep and it's almost like you can sense them coming. "I'm not sure if it's the pressure in your home that wakes you up. But it'll wake you up and then you'll just feel it come through your house. Your bed will shake and your walls are shaking again.

"That's the worst part to me because you're sound asleep." The benefits have become uneven too. Farmers who own mineral rights are quietly making a fortune, but neighbours who own land without them are left out. You can normally tell who is who by the cars they drive, she says. With Oklahoma in the midst of an ongoing drought, farmers are worried about the massive use of water too. When the frackers move in they suck up water wherever they can find it, from dams and streams, even from the side of the road after heavy rain. Wells that used to strike water at 5.8 metres now need to be sunk to 9.7 metres, she says. Still, most of the townsfolk want the industry better regulated rather than banned, she says. In particular they want to see reinjection banned near fault lines. Margie Cink, who has run a main street diner in Medford for 34 years, says the earthquakes have been worth it for the new business the oil brought. "If you come back in a year and the roof has fallen in you'll know I should have been more worried," she says.

A couple of hours down the highway at the town of Stillwater, some residents are more concerned. When Fairfax Media visited this week organisers of an activist group had just met at the local library. One organiser Angela Stills says she believes the Oklahoma state government would trade away the whole state in the pursuit of oil. Another, PhD student Dakota Raynes, describes watching the floor of his home "roll like a wave in the ocean", but he is equally disturbed about the social impacts. Some people feel they have been forced to leave small towns they have lived in all their lives, he says.

Other townsfolk are at each other's throats. Ariel Ross tells of how the anti-fracking signs she puts up in her lawn are constantly vandalised or stolen. This group wants to see fracking banned entirely, but concedes that seems unlikely. Mark Crismon, the Vietnam vet, agrees with them. He says the minerals under his land are worth millions, but that he has chased away the oilmen that offered him money. On Monday morning he sits in the corner of his shed surrounded by oak trees on a bluff above a still lake.

He peers at a laptop sitting on a workbench cluttered with tools, tins of paint and the tails of deer he'd shot on the property. The computer is attached to a seismometer installed by Oklahoma State University, which Crismon is helping with its seismic study. He taps away at the computer and shows off the data gathered earlier in the day. He points to lines that describe a train passing, those that chart nearby drilling, and those that mark a swarm of earthquakes that had hit unnoticed for an hour or so before noon. Some of his neighbours want to sell up and get out, he says. Others, like him, plan to stay whatever the future brings.

"The oil companies own everyone in Oklahoma, but they don't own me," he says. "I write my own pay check."