Dear Brett
I have a copy of Charles Richter's Book "Elementary Seismology"
(published in 1957) and the practical definition of an earthquake is
the release of energy in the geologic strata due to accumulated shear
stress.

The resulting seismic radiation will consist if a longitudinal wave
(pressure wave) and a transverse wave (shear wave) and a seismographic
record of the event would have the classic P and S pattern.

Shear stress can be induced by large or small scale forces. The
largest and most common cause of shear stress is plate tectonics,
However shear forces on a small scale can be induced by excavation in
rock formations such as mine tunnels. As material is removed from a
mine tunnel, the surrounding rock formations forming the ceiling will
become unsupported and it will sag and subject to shear stress and
strain.

If the ceiling collapses, the release of the shear strain will produce
a pressure wave and a transverse wave which is considered a true
earthquake. There was a severe mine collapse in Utah and seismographs
indicated the classic P and S waves and the event had a magnitude of
at least 4.1.

Shear stress/strain is also present in glaciers and it is well known
to residents in the Arctic regions that earthquake like events occur
due to breakage of large blocks of ice.

Galen

On Mon, Dec 10, 2012 at 4:39 PM, Brett Nordgren  wrote:
> Thomas,
>
> I can only offer my opinion.  Yes, I believe these should be called
> earthquakes.  The energy being released even in quite a small quake is much
> larger than the energy put into the ground by the pressure and volume of the
> hydraulic fracturing fluid.  Man-made activities would appear to just be
> triggering the release of strain energy which is already present.  They are
> earthquakes which are simply happening sooner (and smaller?) than they would
> have if left alone.
>
> Just my two cents.
>
> Brett
>
>
> At 11:53 AM 12/10/2012, you wrote:
>>
>> With the holidays and all, this is not the best time of year to bring this
>> up but maybe somebody who knows is listening. ...so here goes. The basic
>> question is when is an earthquake an earthquake. I have been around long
>> enough that I recognize/ignore mine blasting. And should I
>> also ignore fracking? Well water removal? Injection well activity? What
>> about this
>> http://theadThomavocate.com/home/4538683-125/assumption-sinkhole-burps-vegetation-hydrocarbons?
>> I believe that earthquakes are defined as the reduction of stress along
>> breaks/faults in the crust. Isn't that what is happening in almost all of
>> these cases? Does it really matter than man caused these? Is it the size?
>> Isn't the activity  just as scientifically important as truly "real" minor
>> earthquakes like those along the New Madrid and San Andes fault?
>
>
>
>
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