## PSN-L Email List Message

Subject: Re: Digest from 01/21/2007 00:00:40
From: Randall Peters PETERS_RD@..........
Date: Mon, 22 Jan 2007 09:47:19 -0500

Roger, I have respnded to your request for help; i.e.,
"This brings up a very important point--what is the pendulum sensor
reading?   Is it acceleration, velocity, or displacement?  I need help here. "

With all the confusion as to how a seismometer functions, one has to wonder if Einstein was
the only one who ever acquired a complete conceptual
mastery of inertia. His principle of relativity states that the ``laws of physics remain the
same for any non-accelerating frame of reference''. In
practical terms, this equivalence of inertial reference frames means that it is impossible
to detect uniform motion on the basis of measurements
conducted inside a box, such as a seismometer. Thus the only feature of motion having any
importance whatsoever to a seismometer is acceleration
of the case that supports its inertial mass M. It is very common to erroneously believe that
any type motion of the case will be met with displacement
of M relative to the case, because of the inertia of M. Be sure to understand that the only
property of the motion that is ``resisted'' by M is the
acceleration. Thus the acceleration is the only thing that can be directly measured!!
Velocity and position, the other kinematic variables so frequently
discussed in seismology, can only be inferred from the acceleration measurement. Unlike the
quintessential acceleration, they cannot be directly
measured, even though they are frequently specified.
The output from a seismometer is directly proportional to acceleration, as long as the
acceleration takes place at a frequency
lower than the natural (eigen) frequency of the instrument, and additionally, it is
operating with damping that is near critical. When the frequency of
the drive is higher than the natural frequency of the instrument, the response of the
instrument is attenuated by the ratio of the square of the drive
frequency to the square of the eigenfrequency. If one is talking about the ground
displacement, as opposed to the acceleration, just the opposite
behavior is found. For those who want to believe that a seismometer responds directly to
ground displacement, complete confusion results.
It is also important to note that the horizontal seismometer, such as a pendulum,
responds to more than one type of acceleration. From ``inside the
box'' of the instrument there is no way to distinguish between these two forms of
acceleration, which are (i) horizontal acceleration of the instrument,
and (ii) changes in orientation of the box (tilt) relative to the direction of the local
field of the earth g of the earth, having the magnitude of 9.8 m/s2.
Randall

psn-l-digest-request@.............. wrote:

> .------ ------ ------ ------ ------ ------ ------ ------ ------ ------.
> | Message 1                                                           |
> '------ ------ ------ ------ ------ ------ ------ ------ ------ ------'
> Subject: RE: Pendulum Q
> From:    "Stephen Hammond"
> Date:    Sun, 21 Jan 2007 00:40:20 -0800
>
> Boy, this is getting a little mixed up. Are we talking about the
> response of the instrument or the site response of the recording
> location?
> Regards, Steve Hammond PSN San Jose, Aptos Ca.
>
> -----Original Message-----
> From: psn-l-request@.............. [mailto:psn-l-request@...............
> On Behalf Of Larry Cochrane
> Sent: Saturday, January 20, 2007 10:52 PM
> To: psn-l@..............
> Subject: Re: Pendulum Q
>
>  From Randall. -Larry
>
> Notice, Bob, what I said about the matter.  If the 'purity' of the
> events is not
> what you are most interested in, then give it a try.  The 'carrier' (a
> misnomer)
> you mention is not 20 Hz but 50 mHz (much lower frequency than body wave
> values).  There is useful information concerning the energy of the
> earthquake by
> doing the power spectral density (corrected for the transfer function of
> the
> instrument; i.e., the transient, or 'ringing' features)-- independent of
> the
> 'events'.  My guess is that most people don't really use the details of
> the event
> information quantitatively anyway.  You go find out where the earthquake
> occurred
> by consulting USGS webpages after you've seen it on your seismograph.
> It is not
> the time difference between P and S events that serves as the primary
> means for
> locating an earthquake by USGS anyway.  The errors of a calculation
> based on the
> difference in speeds of the longitudinal and transverse components are
> much worse
> than a calculation using only the P event from two or more instruments
> geographically separated in azimuth by a large amount relative to the
> earthquake.  In other words, USGS uses triangulation as the means for
> localizing
> earthquakes.  Yes it is nice to observe the S wave delay relative to the
> P wave
> as a rough measure of how far away the earthquake was.  I figured,
> however, that
> some of you would like to just 'see' the surface waves from weaker,
> distant
> earthquakes.  I predict that by the means I mentioned you will see some
> of them
> that otherwise would go unnoticed.  Before anybody makes sweeping
> generalizations
> about my heresy, I suggest that you first take a look at the graphs that
> I have
> posted on my webpage at http://physics.mercer.edu/hpage/listserve.gif
> It shows
> that the undamped pendulum (in spite of ringing, following arrival of
> each of the
> P and S waves for the case shown-- nevertheless contains decent
> information
> concerning the spectral features of the most important piece of the
> record; i.e.,
> the surface waves, whose frequencies are distributed between
> approximately 7 s
> and 70 s.  The very longest periods differ between the VolksMeter record
> and the
> undamped pendulum record (PSD's), but this might be due in part to the
> different
> locations of the instruments.  The undamped instrument was on a
> home-built 'pier'
> in my home basement, whereas the VolksMeter was on the concrete-slab
> floor of the
> Willett Science Center here at Mercer University (about two miles from
> my
> house).  The building may be hindered with respect to the tilts
> occurring at the
> longest periods.  For you 'purists', note the fact that the
> first-disturbance
> arrival times of both P and S are abundantly clear, including the delta
> time
> between them--closely correlated with the 'proper' instrument, our
> VolksMeter.  I
> expect similar results with an undamped, tuned garden-gate pendulum with
> a period
> 5 times longer at 20 s--the big difference being that the surface waves
> that
> characterize the teleseismic earthquake record will be enhanced
> significantly
> because their frequencies are close to the high-Q resonance of the
> instrument.
>
> Randall
>
> __________________________________________________________
>
> Public Seismic Network Mailing List (PSN-L)
>
> To leave this list email PSN-L-REQUEST@.............. with
> the body of the message (first line only): unsubscribe
>
> .------ ------ ------ ------ ------ ------ ------ ------ ------ ------.
> | Message 2                                                           |
> '------ ------ ------ ------ ------ ------ ------ ------ ------ ------'
> Subject: Re: Pendulum Q
> From:    ian
> Date:    Sun, 21 Jan 2007 16:37:25 +0000
>
> it would be interesting to compare signals from the same pendulum in a
> damped and undamped state, for similar events, if the data is available.
>
> Ian
>
> .------ ------ ------ ------ ------ ------ ------ ------ ------ ------.
> | Message 3                                                           |
> '------ ------ ------ ------ ------ ------ ------ ------ ------ ------'
> From:    "tchannel"
> Date:    Sun, 21 Jan 2007 10:39:32 -0700
>
> This is a multi-part message in MIME format.
>
> ------=_NextPart_000_0057_01C73D48.70008390
> Content-Type: text/plain;
>         charset="iso-8859-1"
> Content-Transfer-Encoding: quoted-printable
>
> Hi Folks,  I did receive a nice recording of the 7.3M Molucca Sea, which =
> was 108.5 degrees, 12063km from Boise Id.
> I was under the impression that this event would not be visible as it =
> fall between the 103 and the 143.  The  P and S shadow zones.
> The P is very visible and the S? not sure.   Could this be? or am I just =
> seeing other things which I think are the P and the S?
> Nice recording anyway.  Thanks, Ted
> ------=_NextPart_000_0057_01C73D48.70008390
> Content-Type: text/html;
>         charset="iso-8859-1"
> Content-Transfer-Encoding: quoted-printable
>
>
>
>  charset=3Diso-8859-1">
>
>
>
>
>
Hi Folks,  I did receive a nice = > recording of=20 > the 7.3M Molucca Sea, which was 108.5 degrees, 12063km from Boise=20 > Id.
>
I was under the impression that this = > event would=20 > not be visible as it fall between the 103 and the 143.  The  P = > and S=20 > shadow zones.
>
The P is very visible and the S? not=20 > sure.   Could this be? or am I just seeing other things which = > I think=20 > are the P and the S?
>
Nice recording anyway.  Thanks,=20 > Ted
> > ------=_NextPart_000_0057_01C73D48.70008390-- > > .------ ------ ------ ------ ------ ------ ------ ------ ------ ------. > | Message 4 | > '------ ------ ------ ------ ------ ------ ------ ------ ------ ------' > Subject: Re: Shadow Zone > From: =?ISO-8859-1?Q?J=F3n_Fr=EDmann?= > Date: Sun, 21 Jan 2007 17:46:00 +0000 > > Hi > > I did also record the 7.2Mw event. But the P wave was delaed due to the > shadow zone. USGS has a map of P wave times and the shadow zone here, > http://neic.usgs.gov/neis/eq_depot/2007/eq_070121_xvam/neic_xvam_t.html > > Regards. > -- > Jón Frímann > http://www.jonfr.com > http://www.simnet.is/jonfr500/earthquake/ > > .------ ------ ------ ------ ------ ------ ------ ------ ------ ------. > | Message 5 | > '------ ------ ------ ------ ------ ------ ------ ------ ------ ------' > Subject: Shadow Zone > From: "tchannel" > Date: Sun, 21 Jan 2007 11:04:09 -0700 > > This is a multi-part message in MIME format. > > ------=_NextPart_000_0076_01C73D4B.DFFFE700 > Content-Type: text/plain; > charset="iso-8859-1" > Content-Transfer-Encoding: quoted-printable > > Perhaps, I am seeing the=20 > Pdif (old:Pdiff) P diffracted along the CMB in the mantle =20 > > Using Winquake and the View/Phases/Display, I see the first part = > labeled "Pdiff" and no P or S labeled. This is my first event which was = > in the Shadow. Winquake is a Very nice tool. Thanks, Ted > ------=_NextPart_000_0076_01C73D4B.DFFFE700 > Content-Type: text/html; > charset="iso-8859-1" > Content-Transfer-Encoding: quoted-printable > > > > charset=3Diso-8859-1"> > > > > >
Perhaps,  I am seeing the
>
> > > > >
 Pdif (old:Pdiff) P diffracted along the CMB in the mantle=20 >
>
Using Winquake and the View/Phases/Display,  I see the first = > part=20 > labeled "Pdiff" and no P or S labeled.  This is my first event = > which was in=20 > the Shadow.   Winquake is a Very nice tool.   = > Thanks,=20 > Ted
Randall Peters wrote:
>

>
Notice, Bob, what I said about the matter.  If the 'purity' of the= > =20 > events is not what you are most interested in, then give it a try.  The= > =20 > 'carrier' (a misnomer) you mention is not 20 Hz but 50 mHz (much lower frequ= > ency=20 > than body wave values).  There is useful information concerning the ene= > rgy=20 > of the earthquake by doing the power spectral density (corrected for the=20 > transfer function of the instrument; i.e., the transient, or 'ringing'=20 > features)-- independent of the 'events'.  My guess is that most people=20 > don't really use the details of the event
information quantitatively=20 > anyway.
>

>
Hi Randall,
>

>
I guess I am not like "most people". I try very hard to keep my=20 > sensors calibrated and as broadbanded as required to accurately sense and=20 > reproduce all phases, and my timing within a fraction of a second. I am= > not=20 > particularly interested in the L phases, except for estimating direction. If= > you=20 > look at my Molucca Sea event file, 070121.114300.rem.psn, you will not find=20= > the=20 > extra hour it took to receive the L waves.
>

>
Sorry, but I will not even think of trying what you suggest. V> >

>
Nor am I interested in displacement sensing. I tried that a long= > =20 > time ago, and all my dynamic range was used up by uncontrollable tilts=20= > and=20 > drift. If I want to see displacement, I integrate my velocity data after hig= > h=20 > pass filtering it with my own design zero lag filter to exclude signals= > =20 > lower than 0.025 Hz.
>

>
Bob
> > -------------------------------1169417185-- > > .------ ------ ------ ------ ------ ------ ------ ------ ------ ------. > | Message 8 | > '------ ------ ------ ------ ------ ------ ------ ------ ------ ------' > Subject: Re: Shadow Zone > From: Bobhelenmcclure@....... > Date: Sun, 21 Jan 2007 17:33:12 EST > > -------------------------------1169418792 > Content-Type: text/plain; charset="US-ASCII" > Content-Transfer-Encoding: 7bit > > The direct P phase is not detected beyond 103 degrees because it is in the > shadow of the core. There are phases which pass through the core. If you want > a good picture of how seismic waves propagate, try running the Seismic Waves > program by Alan Jones, _http://www.geol.binghamton.edu/faculty/jones/_ > (http://www.geol.binghamton.edu/faculty/jones/) > > I have a program "Travel Time" which might also be useful. It plots and > uses the Jeffreys and Bullen Seismological Tables to list the time of arrival of > an event at your station coordinates. Just enter your station coordinates, > and the event line from NEIC, load file "BigList.jb1, and you can get travel > and arrival times for all JB files listed to the clipboard, and a plot of all > phases for all distances. The program can be downloaded from: > > _http://www.jclahr.com/science/psn/mcclure/traveltime/index.html_ > (http://www.jclahr.com/science/psn/mcclure/traveltime/index.html) > > For a discussion of some special core waves, consult > > _http://www.seismosoc.org/publications/SRL/SRL_72/srl_72-1_eq.html_ > (http://www.seismosoc.org/publications/SRL/SRL_72/srl_72-1_eq.html) > > Hope this is helpful > > Bob > > -------------------------------1169418792 > Content-Type: text/html; charset="US-ASCII" > Content-Transfer-Encoding: quoted-printable > > > > > > Arial"=20 > bottomMargin=3D7 leftMargin=3D7 topMargin=3D7 rightMargin=3D7> e_document=20 > face=3DArial color=3D#000000 size=3D2> >
The direct P phase is not detected beyond 103 degrees because it= > is=20 > in the shadow of the core. There are phases which pass through the core. If=20= > you=20 > want a good picture of how seismic waves propagate, try running the Sei= > smic=20 > Waves program by Alan Jones,  href=3D"http://www.geol.binghamton.edu/faculty/jones/">http://www.geol.bingh= > amton.edu/faculty/jones/
>

>
I have a program "Travel Time" which might also be useful. It pl= > ots=20 > and uses the Jeffreys and class=3DSpellE>Bullen Seismological Tables to list the time of arriva= > l of=20 > an event at your station coordinates. Just enter your station coordinates, a= > nd=20 > the event line from NEIC, load file "BigList.jb1, and you can get trave= > l=20 > and arrival times for all JB files listed to the clipboard, and a plot of al= > l=20 > phases for all distances. The program can be downloaded from:
>

>
href=3D"http://www.jclahr.com/science/psn/mcclure/traveltime/index.html">htt= > p://www.jclahr.com/science/psn/mcclure/traveltime/index.html
>

>
For a discussion of some special core waves, consult
>

>
href=3D"http://www.seismosoc.org/publications/SRL/SRL_72/srl_72-1_eq.html">h= > ttp://www.seismosoc.org/publications/SRL/SRL_72/srl_72-1_eq.html
>

>
>

>
Bob
> > -------------------------------1169418792-- > > .------ ------ ------ ------ ------ ------ ------ ------ ------ ------. > | Message 9 | > '------ ------ ------ ------ ------ ------ ------ ------ ------ ------' > Subject: Re: Pendulum Q > From: ChrisAtUpw@....... > Date: Sun, 21 Jan 2007 19:05:43 EST > > -------------------------------1169424343 > Content-Type: text/plain; charset="US-ASCII" > Content-Transfer-Encoding: 7bit > > In a message dated 21/01/2007, Bobhelenmcclure@....... writes: > > Sorry, but I will not even think of trying what you suggest. > > Hi Bob, > > Entirely your choice! But don't discourage others from experimenting. > > Nor am I interested in displacement sensing. I tried that a long time ago, > and all my dynamic range was used up by uncontrollable tilts and drift. > > Which could have told you quite a lot about your equipment and how to > improve it? > Try LVDT or capacitative detectors some time? You might like one of them! > My LVDT seems to work fine. Professional systems tend to use > capacitative types. > > Regards, > > Chris Chapman > > -------------------------------1169424343 > Content-Type: text/html; charset="US-ASCII" > Content-Transfer-Encoding: quoted-printable > > > > > > Arial"=20 > bottomMargin=3D7 leftMargin=3D7 topMargin=3D7 rightMargin=3D7> e_document=20 > face=3DArial color=3D#000000 size=3D2> >
In a message dated 21/01/2007, Bobhelenmcclure@....... writes:
> style=3D"PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: blue 2px solid"><= > FONT=20 > style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= > =3D2> >
>
Sorry, but I will not even think of trying what you=20 > suggest.
>
Hi Bob,
>

>
Entirely your choice! But don't discourage othe= > rs=20 > from experimenting.
> style=3D"PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: blue 2px solid"><= > FONT=20 > style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= > =3D2> >
Nor am I interested in displacement sensing. I tried that a lo= > ng=20 > time ago, and all my dynamic range was used up by uncontrollable tilt= > s=20 > and drift.
>
>
Which could have told you quite a lot about you= > r=20 > equipment and how to improve it?
>
Try LVDT or capacitative detectors some time? Y= > ou=20 > might like one of them!
>
My LVDT seems to work fine. Professional system= > s=20 > tend to use capacitative types.
>

>
Regards,
>

>
Chris Chapman
> > -------------------------------1169424343-- > > .------ ------ ------ ------ ------ ------ ------ ------ ------ ------. > | Message 10 | > '------ ------ ------ ------ ------ ------ ------ ------ ------ ------' > Subject: Molucca Sea Earthquake > From: "Michael Kimzey" > Date: Sun, 21 Jan 2007 22:24:17 -0500 > > Hi all. > > Very good discussions here on the list. I just recorded my very first > earthquake and am HOOKED! Totally incredible that this thing of plumbing > supplies and magnets could pick up vibrations from across the world. > > Ok...some questions, especially because I would like to share this data if > anyone wants it. > 1) is there someplace (FAQ or such) that directs how to set up the alarms in > WinSDR? > 2) What should I do with the .psn file if others want it (do I send it to > somebody?) > > On my system, the waves could be seen on the graph for 90 minutes, is this > normal or is my Lehman underdamped? > > Thanks for any feedback or links to FAQ's that I missed. > > PS, if there is anyone that has one of Larry's SG electronics boards that > they want to part with, please email me directly. > > - Mike > > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-DIGEST-REQUEST@.............. with > the body of the message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information.