Monday, August 6, 2007

Utah Mine Collapses: Caused by a Quake?

This morning, the Deseret Morning News reported that six people may be be trapped in a coal mine near Huntington, UT. Rescuers are searching for the miners, but haven't yet been able to reach them. The miners were trapped when a section of the mine caved in.

As the search continues, scientists are trying to understand what might have caused the incident. Seismograph readings show that close to the mine, there were vibrations in the earth around the time of the cave-in. The jolt measured 3.9 on the Richter Scale.

The hard part is knowing whether there was an earthquake that caused the mine to collapse, or if the collapse itself is what caused the earth to shake.

"Normally, rocks in the Earth's crust are constantly subjected to pressures from all sides. This is called a confining pressure. However, the mining of coal leaves a low pressure zone (empty space). After mining, pressures are still being applied to the rock on all other sides, except at the wall of the tunnel. If the rock is not strong enough to withstand this stress, the wall of the mine tunnel gives way. These "bursts" are well named because there is often no warning and large rocks can be thrown horizontally or vertically, as well as drop from the ceiling during these events. In addition to these relatively small rock bursts, more catastrophic "implosional" failures can also occur on a much larger scale. Sometimes large sections of mines can collapse.

"Mine tremors", rock bursts or mine collapse events, are recorded on seismograph instruments in exactly the same manner that earthquakes are recorded."

We still don't know what caused today's incident, but the U of U Seismograph Stations say that in the Utah coal belt, about 1/4 of tremors are a result of mining, while 3/4 are natural earthquakes.