And the type of mining they were doing was particularly dangerous. When they mine a vein of coal, they follow the vein leaving pillars of coal to hold up the ceiling. When the vein has played out they try to get out the last of the coal by collapsing the pillars as they retreat and sending the coal to the top on a conveyor belt. Of course, in the process, there is a lot of additional colllapse. Most of the passages are about 8' high and 18' wide--pretty roomy compared to cave passageways. The problem is, as you can ascertain, it makes for a very unstable situation.
Even more, I've been concerned about the callous attitude of Bob Murray, owner of the mine. To see a bit of his attitude, check out the Salt Lake City Tribune article:
http://www.sltrib.com/ci_6564581
I continue to hope for the best, but fear the worst.
Louise
From: dirt...@comcast.net
To: Texascavers@texascavers.com (Cave Texas)
Subject: [Texascavers] Natural Earthquakes vrs Mine Collapse
Date: Fri, 10 Aug 2007 19:42:14 +0000
Received: from raistlin.wokka.org ([69.56.185.90]) by bay0-mc3-f20.bay0.hotmail.com with Microsoft SMTPSVC(6.0.3790.2668); Fri, 10 Aug 2007 12:42:56 -0700
Received: (qmail 27992 invoked by uid 89); 10 Aug 2007 19:42:54 -0000
Received: (qmail 27983 invoked by uid 31338); 10 Aug 2007 19:42:54 -0000
Natural Earthquakes vrs Mine Collapse
The discussion in the press involves a lot more than basic physics. Egos, liability, and more are behind the comments reported in the press.
From the physics standpoint, point-explosions (whether quarry blasts, nuclear tests, or most mine collapse) produce seismic records that are quite distinct from earthquakes.
Earthquakes are messy things. They release stress that has built up along a fault over a long period of time. The fault does not tear all at once, so there is a fairly long period of time during which the rupture occurs. Once that first failure occurs, then there is a period of stress readjustment and �aftershocks� when additional failure occurs at points close to the initial fracture, which release the rest of the built-up stress. Therefore natural earthquakes produce a seismic record that is very messy and complicated, with a lot of wiggles and juggles.
Point explosions are relatively neat. The seismic record produced is usually a sharp big jiggle followed by a decreasing series of smaller wiggles � like a single beat on a big drum. That is how we can tell if a foreign power makes an unreported nuclear test. Such a test does not produce the same kind of messy seismic signal as that produced by an earthquake.
A large mine collapse can be somewhere in between, so it is not necessarily immediately clear what occurred. The first bang caused by the initial mine collapse can be followed by secondary collapses as stress is redistributed and adjacent parts of the mine collapse as a result. Each collapse event, however, produces a distinct and sharp signal.
So the academic seismologists have very good reasons when they say �It does not look like a natural earthquake�.
My bet is with them.
Dirtdoc
---------------------------------------------------------------------
Visit our website: http://texascavers.com
To unsubscribe, e-mail: texascavers-unsubscr...@texascavers.com
For additional commands, e-mail: texascavers-h...@texascavers.com
