On 2012-07-01 12:48, Brett Nordgren wrote:
> 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.

Isn't First Time of arrival important to tomography ?
To the average velocity of the various phases ?




>
> 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.

I saw a device at Arizona State University which could measure
three components of velocity using only two inverted pendulums
at possibly a 45 degree angle to the vertical pointing N/s and E/w.
It was all open for everyone to see how it worked. located
at the physics building.

Possibly you know who built the device or what
it real name would be ?

I have not seen such a device on the internet
and am sure other designs exist which are
not being talked about.

I should imagine math or special circuits
are needed to extract the vertical
from the two sensors.



>
> Hope this helps,
> Brett
>
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