[TowerTalk] Tower Stress in a quake?

[Roger (K8RI) on TT]

Just curious as the only quakes MI has felt were collapsing coal, 
copper, and salt mines or from quakes many hundreds of miles away.  
Michigan has a number of tiny fault lines that are relatively shallow. 
None that I could find active. There is a thick block of solid 
underlying material that makes finding deep or major faults difficult, 
So earthquakes are rare as are almost all that can be attributed to 
fracking.

Coming from such a benign area, that makes me wonder what  seismic 
activity, or risk is taken into account.  Earthquake history for the 
area?  Distance to the nearest active fault or faults.  Soil capable of 
liquefaction, and at what magnitude quake is used for the calculation?  
Magnitude of the vertical and horizontal waves? (Don't remember the names).

I'd think quakes that cause fragile brick chimneys to fall would be a 
non issue for towers.

I don't know about the shale underlying Texas, but mid and Northern US 
have huge shale areas, that are deep, thick, and cover many states and 
parts Canada.

I would think (meaning I don't know) that fracking would be limited to 
miles. A large operation with many wells and injection sites might cover 
hundreds of square miles, but does fracking break up the shale in a 
small area, or are there long splits.

The oil and gas is dissolved and held tightly in the shale, so I'd think 
the smaller the pieces the more they'd get out of it.  I don't think the 
fracking process would remove material causing voids as has the deep 
well water removal that has caused many feet of subsiding.  
http://water.usgs.gov/edu/earthgwlandsubside.html makes for interesting 
reading

73

Roger (K8RI)





On 7/27/2015 6:11 PM, Steve Jones wrote:
> Installing microwave radio systems for Harris Corporation over 20 years, I
> had to obtain building permits for many new towers (eg. 100-300', both guyed
> and self-supporting).  The engineering calculations included stresses from
> earthquakes as well as wind.  The stress from wind on the guys and/or
> foundation bolts was always 10x the forces exerted by earthquakes.  If your
> tower design is adequate for the winds in your area, I would not worry about
> earthquake forces.
>
> 73,
> Steve
> N6SJ
<one whale of a lot of snip>

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