One of the most significant factors is the focal mechanism of the event. =
 This is displayed as a "Beech Ball".  This covers the three variable =
axis of an event which are strike (orientation from north), dip (the =
angle of the fault measured from horizontal), and slip or rake ( =
movement of the hanging wall against the foot wall - measured from =
horizontal).  Here is a link to a USGS presentation on focal mechanism.

nctr.pmel.noaa.gov/education/ITTI/seismic/Focal_mech_USGS.ppt

One other minor factor to consider is that shear waves are actually made =
up of two components, SH - horizontal component, and SV - vertical =
component.  It could be the orientation of the equipment is picking up =
either the SV or SH component and that may not necessarily be the =
strongest component of the wave.=20

Following is a link to a program that allows to enter the data from an =
event and see a visualization of the focal mechanism (Beech Ball."  NOTE =
- This program requires Java to be installed on your computer.

Seismic Body-Wave Polarity Modeler

Bob Hancock


nctr.pmel.noaa.gov/education/ITTI/seismic/Focal_mech_USGS.ppt


On Jul 11, 2012, at 7:34 AM, Geoff wrote:

> On 2012-07-01 12:48, Brett Nordgren wrote:
>> Hello Geoff,
>>=20
>> Yes, lots of  ETC.  I'll give it try.
>>=20
>> At 07:57 PM 6/29/2012, Geoff GM wrote:
>>> Hello PSN:
>>>=20
>>> 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.
>>>=20
>>> 1. Will shear waves pass through the Mantel ?
>>=20
>> 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.
>>=20
>>>   (Mantel is partially liquified ?)
>>>=20
>>> 2. Does the solid core spin faster by one rotation in four hundred
>>> years ?
>>>=20
>>> (I heard this a long time ago but not sure its for real ?)
>>=20
>> 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.
>>=20
>>> Don't just point me to some web site,
>>=20
>> 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.
>>=20
>>> Id like to hear your own opinions on these ideas ?
>>>=20
>>> 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).
>>=20
>> 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.
>>=20
>> 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.
>>=20
>>> I used 4 rare earth magnets to determine the constant
>>> with about 1 inch of gap where the coil was located.
>>>=20
>>> 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 ??
>>=20
>> 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.
>>=20
>>> With this "G" constant I need a gain of about X11
>>> over what I currently am using built be the pros.
>>>=20
>>> 
>>>=20
>>> 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.
>>=20
>> 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/tuto=
rial
>>=20
>> you can see how with real earthquakes, both wavefront travel and =
ground
>> motion can be clearly observed in a large array.
>>=20
>>> 6. is it possible to build an omnidirectional sensor
>>>   instead of three directionals' to see the motion.
>>=20
>> 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.
>=20
> Isn't First Time of arrival important to tomography ?
> To the average velocity of the various phases ?
>=20
>=20
>=20
>=20
>>=20
>> 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.
>=20
> 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.
>=20
> Possibly you know who built the device or what
> it real name would be ?
>=20
> I have not seen such a device on the internet
> and am sure other designs exist which are
> not being talked about.
>=20
> I should imagine math or special circuits
> are needed to extract the vertical
> from the two sensors.
>=20
>=20
>=20
>>=20
>> Hope this helps,
>> Brett
>>=20
>> __________________________________________________________
>>=20
>> Public Seismic Network Mailing List (PSNLIST)
>>=20
>> To leave this list email PSNLIST-REQUEST@.............. with the body =
of
>> the message (first line only): unsubscribe
>> See http://www.seismicnet.com/maillist.html for more information.
>> .
>>=20
>=20
>=20
> __________________________________________________________
>=20
> Public Seismic Network Mailing List (PSNLIST)
>=20
> To leave this list email PSNLIST-REQUEST@.............. with the body =
of the message (first line only): unsubscribe
> See http://www.seismicnet.com/maillist.html for more information.
>=20


nctr.pmel.noaa.=
gov/education/ITTI/seismic/

Seismic =
Body-Wave Polarity Modeler

Bob =
Hancock


nctr.pmel.noaa.=
gov/education/ITTI/seismic/Focal

On Jul 11, 2012, at 7:34 =
AM, Geoff wrote:

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.

<clip>

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/visua=
lizations/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

__________________________________________________________

Public Seismic Network Mailing List =
(PSNLIST)

To leave this =
list email PSNLIST-REQUEST@............
COM with the body of
the =
message (first line only): unsubscribe
See http://www.seismicnet.com=
/maillist.html for more information.
.



___________________________________=
_______________________

Public Seismic Network Mailing List =
(PSNLIST)

To leave this list email PSNLIST-REQUEST@............
COM with the body of the message (first line only): =
unsubscribe
See http://www.seismicnet.com=
/maillist.html for more =
information.


=