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Storm clouds hover over a field in Oklahoma. Geologists there have been chasing down an unusual signal in their seismic data that grew in frequency and spread as the summer wore on.
A buzz that rocked the state all summer sent geologists on a labyrinthine chase—and unearthed new mysteries about how energy moves through land and air.
It all started when a wave swept across Oklahoma on June 24, just before 11:11 a.m. local time. It buzzed one seismometer after another, seeming to ping-pong hundreds of miles across the state. This wave didn’t just breeze by—it pulsed like a geologic heartbeat for about 10 minutes.
“Well, that’s odd,” geophysicist Jake Walter at the Oklahoma Geological Survey remembers thinking. He had spotted the regular pulse as it scrolled across a big flat screen TV in the OGS seismic lab. At first he thought it might be a glitch in the monitoring devices, but when that happens, the signal is usually limited to a single instrument. That morning’s buzz, as he later found out, rattled 52 stations across the state.
Andrew Thiel, an OGS analyst tasked with investigating the event, traced similar signals back to at least March. Through the summer, the waves swept across the state with increasing frequency, intensity, and spread, sometimes sticking around for more than 20 minutes. But they always happened in the morning, and never on a Sunday.
After a labyrinthine chase, the team has now discovered at least part of the answer: The strange signals originate from the McAlester Army Ammunition Plant. But even with a source in hand, the case is far from closed. Scientists are still digging for clues to how the waves traveled so far, and why they changed over time.