Hello Geoff,

Yes, lots of  ETC.  I'll give it try.

At 07:57 PM 6/29/2012, Geoff GM wrote:
>Hello PSN:
>
>Id like to hear from you guys (or gals :-) )
>why some quakes will show no Shear waves.
>Or possibly, so small you cant see them with the naked eye.
>
>1. Will shear waves pass through the Mantel ?

Yes.  And that defines the boundary between the mantle and the outer 
core.  The S waves will travel through the mantle but they bounce off 
the outer core.

>    (Mantel is partially liquified ?)
>
>2. Does the solid core spin faster by one rotation in four hundred years ?
>
>(I heard this a long time ago but not sure its for real ?)

In the past decade there had been studies based on indirect 
measurements that suggested that the core was rotating relative to 
the earth's surface by up to 1 degree per year.  A careful study 
published last year, done by measuring the travel times of earthquake 
waves passing through the inner core, as compared to ones reflecting 
from it, suggested that its rate of rotation was roughly a million 
times slower than that.  I think we'll just have to wait for the 
community to sort out who and what are right, and I'm sure they 
will.  For now, I'll bet on the slower number.

>Don't just point me to some web site,

However, that's where you can find the answers.  It's just that you 
need to be able to separate quality scientific observations from 
someone's opinion.

>Id like to hear your own opinions on these ideas ?
>
>3. I wound a coil out of like AWG30 copper wire
>It had a Resistance of 86 ohms and it seems to have
>a generator constant of about (0.242V/(IN/sec))
>Does that sound realistic for a not-so-carefully
>wound coil (Wound like a bobbin of thread).

Yes.  .242 V/in/sec / .0254 m/in gives 9.5 V/m/sec which also 
represents a forcing constant of 9.5 N/A.  In our 
force-balance-vertical forcing coils we see from 6 to about 15 N/A 
depending on the coil/magnet size.  Depending on how much noise there 
is in your instrument and at your site, it will probably need some 
amplification to get optimum sensitivity, perhaps x10.  More turns of 
finer (#40?) wire might be better if for some unknown reason you 
couldn't amplify the signal.

Bobbin winding is actually superior in some ways to layer winding so 
long as the voltages are modest.  My wire table says that #30AWG with 
heavy film insulation, random-wound, gets about 6550 turns per square 
inch of coil cross-section, while in a typical layer-wound coil, 
using the same wire, you could expect about 5160 turns/sq in., or 21% 
fewer turns.

>I used 4 rare earth magnets to determine the constant
>with about 1 inch of gap where the coil was located.
>
>I figure by this it would be best to pay a pro
>to wind a proper 1K coil out of AWG30 wire
>or a 10K coil out of 40AWG copper wire ??

With practice I think you could wind a coil even with #40.  The 
inside surface of the bobbin has to be quite smooth so that it can't 
snag the wire.  You lay the wire spool on its side on the floor or 
other horizontal surface and let the wire spiral off the top side so 
that there's no spool inertia to break or snarl the wire (the small 
amount of twisting won't matter) and you provide (very slight) 
tension by lightly holding the wire between a couple of small, thick 
felt pads.  If you keep perhaps a foot of distance between the coil 
you are winding and the point where the wire is being held, it should 
wind itself almost level without your doing much of anything to guide 
it.  I haven't done this myself, but I have watched it being done and 
it didn't look all that difficult.  BTW In production winding, with 
fine wire, they typically spin the bobbin very fast--maybe thousands 
of RPM.  To make a coil I should think that you would just have to 
practice, take your time and use a little care.

>With this "G" constant I need a gain of about X11
>over what I currently am using built be the pros.
>
>
>
>5. Do most seismic waves arrive from below or the sides , and
>     can you tell direction by time delay between two stations or more ?
>     Not by drawing lines on a map ? Not by N/S E/W knowledge of motions.

Both.  Surface waves come from the sides.  Body waves can arive 
anywhere from nearly straight below to nearly horizontal.  **However, 
there is a big difference between the direction from which a 
wavefront arrives and the direction of the ground motion it 
causes.**  It would take more than two stations, ideally lots of 
them, to give you a good idea of wavefront direction.  In the 
animations 
at 
http://www.iris.edu/hq/programs/education_and_outreach/visualizations/tutorial
you can see how with real earthquakes, both wavefront travel and 
ground motion can be clearly observed in a large array.

>6. is it possible to build an omnidirectional sensor
>    instead of three directionals' to see the motion.

I guess that anything might be possible, but in general, no.  If you 
could, its data would not be very useful scientifically.  Ground 
oscillations have both an amplitude and a 3-d direction (which can 
vary a lot from minute to minute).  An omni sensor would tell you the 
amplitude, but nothing about vibration direction, which is frequently 
not related to wavefront arrival direction.  You would need both 
vibration amplitude and direction to make most scientifically useful 
measurements, which you could get only if you had x, y and z recordings.

For amateur work, a single vertical will probably give the best 
results, since background noise in the vertical direction is much 
lower, especially at amateur sites.  And you really don't miss that 
much by ignoring the horizontal.  Nearly everything except the LQ 
phase usually contains at least some vertical motion.  You could 
simulate an omni instrument by combining x y and z channels from 
three instruments (hard to do properly with voltage signals, but easy 
mathematically on their data).  But the additional noise you'd add 
from the horizontal channels would make it harder to see weak quakes 
than with the vertical alone.  However, I know good verticals aren't 
that easy to make.

Hope this helps,
Brett  


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