The unconfined compressive strength of coal is about 3000 psi. Rock weighs about 160 pounds per cubic foot. Those miners in Utah are about 1500 feet down.
I'm not a mining engineer, but it looks to me like those "seismic bumps" are the mountain telling them that they're too close to the edge. I hope no one else dies before they get the message.
Update: Robert Ferriter of the Colorado School of Mines is a mining engineer. He's surprised that area was still being mined at all.