A 3.5-magnitude earthquake shook central Kansas on Wednesday, jolting an area layered over ancient volcanic rock deep below the surface.

The tremor was detected at 2.14pm local time (3.14pm ET), striking outside Assaria, home to just a few hundred people.

Although Kansas has no active volcanoes, the region marks the southern reach of the Midcontinent Rift System, a massive tectonic event that nearly split North America apart in Earth’s distant past.

When magma forced its way through the crust during that period, it left behind hardened igneous rock and deep fractures that remain buried thousands of feet underground.

The earthquake near Assaria was associated with the Humboldt Fault Zone, a major structural feature stretching across eastern Kansas. 

Geologists say the fault is made up of a series of fractures and buried faults formed hundreds of millions of years ago. 

While it is relatively quiet compared with faults in more seismically active regions, it remains capable of producing small to moderate earthquakes when stress builds along its hidden fractures. 

In areas like Assaria, where the fault intersects layers of ancient volcanic rock, even minor shifts can be detected at the surface as noticeable tremors.

The US Geological Survey (USGS) has received 16 reports of shaking from locals since the earthquake was reported. 

Those living near the episode said the tremor 'sounded like a huge clap of thunder.'

'Didn’t last long, but was loud and strong! I was just north of Assaria, a couple of miles,' one local shared on Facebook.

Others reported that the earthquake shook their cars and homes. 

Scientists say the ancient scars from both the Midcontinent Rift and the Humboldt Fault still matter today, as the North American plate is constantly under slow-moving stress. 

That pressure tends to concentrate along pre-existing weaknesses in the crust, and if enough strain builds, the rock can suddenly slip, releasing energy in the form of seismic waves.

While the volcanoes themselves are long extinct, the structural weaknesses they created more than a billion years ago, combined with the buried faults of the Humboldt Fault Zone, may still help shape where and how earthquakes occur beneath the quiet Kansas plains.

The Humboldt Fault Zone in Kansas is capable of producing moderate to potentially damaging earthquakes. 

The largest known historical event along the fault is estimated to have occurred in 1867, with a magnitude between 5.0 and 5.5.

While the Humboldt Fault is generally less active than more famous seismic zones like the New Madrid Fault, it is connected to the Nemaha Ridge, a major structural feature that can still generate significant tremors. 

Scientists estimate that the fault could potentially produce an earthquake as strong as magnitude 6.5 to 6.7, though most recent activity has been smaller and, in some cases, linked to human activity such as wastewater injection.