I am sorry chaps, but if rock is cracking and breaking, then it is
pretty obvious that stress is moving through the system and not
obviously settling down however gentle it might appear. Put another
way, when a real collapse takes place, you have lost control of your
assumptions and must wait until it truly settles down before you
begin testing your ideas again. Of course, no one wants to do this.
This also naturally implies that stress release in one locale sets up
stress elsewhere especially in a quake environment. For that reason,
we observe long faults taking turns releasing one point after another
sometimes over centuries. What it really tells us is that natural
plasticity prevents permanent freezing of a fault.
In the meantime, the statistics appear to confirm all this as
expected and also gives us a measured likelihood for successor
events. At ten percent, it is not zero but it is a warning to be
awake.
Numbers support
theory large earthquakes can trigger another far away
by Staff Writers
Salt Lake City (UPI) Apr 19, 2013
Big earthquakes can
trigger other quakes far from their geographical center at least 9
percent of the time, a statistical analysis by a U.S. researcher
shows.
With a number of huge
earthquakes in recent years -- in Sumatra, Indonesia, in December
2004, Chile in February 2010 and Japan in 2011 --leading many to
question whether one large quake can cause another on the other side
of the world, Tom Parsons of the U.S. Geological Survey surveyed
catalogs of seismic activity on every continent except Antarctica
going back to 1979.
Of the 260 earthquakes
of magnitude 7 or greater during that period, small earthquakes on
separate fault systems followed in the wake of 24 of them, triggered
by seismic waves passing through distant lands, he said.
"It's a small
hazard, but there is a risk," he said.
Parsons, who presented
his results Friday at the Seismological Society of America annual
meeting in Salt Lake City, says his next step will be to investigate
the 24 quakes that caused far-off events and see if there is anything
special about them.
"So far they look
fairly ordinary. So we're going to have to really dig into them,"
he said.
Seismic activity
during deadly Utah mine collapse yields insights
Salt Lake City (UPI) Apr 19, 2013 - Analysis of seismic activity recorded in a 2007 deadly Utah mine collapse shows its extent was greater than previous studies indicated, researchers say.
The owner of the
Crandall Canyon coal mine initially blamed the collapse, which killed
six miners and three rescue workers, on an earthquake but University
of Utah researchers say analysis of the recordings of the tremor and
hundreds of small aftershocks suggests they were a result of mining
activity and the subsequent collapse.
"We can see now
that, prior to the collapse, the seismicity was occurring where the
mining was taking place and that, after the collapse, the seismicity
migrated to both ends of the collapse zone," said Tex Kubacki, a
graduate student in mining engineering.
Mapping the locations
of the aftershocks "helps us better delineate the extent of the
collapse at Crandall Canyon," he said.
A previous University
of Utah study, based on far fewer aftershocks, said the epicenter of
the collapse was near where the miners were working and the
aftershocks showed the collapse area covered 50 acres.
The new study, based
on data of hundreds of additional aftershocks, has extended the area
of the collapse to the full extent of the western end of the mine,
Kubacki said.
"It's gotten
bigger," he said.
Most of the seismic
activity before the collapse was due to mining, the researchers said,
although they are investigating whether any of those small jolts
might have been signs of the impending collapse.
So far, however,
"there is nothing measured that would have said, 'Here's an
event [mine collapse] that's ready to happen,'" said Michael
"Kim" McCarter, a mining engineering professor and the
study's co-author.
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