PSN-L Email List Message
Subject: RE: [Fwd: hurricane Dennis study]
From: "Kareem at HeyJooJoo" system98765@.............
Date: Tue, 19 Jul 2005 17:49:22 -0700
From: Larry Cochrane [mailto:lcochrane@...............
Sent: Tuesday, July 19, 2005 5:29 PM
Subject: [Fwd: hurricane Dennis study]
I received the following from Dr. Randall Peters. With his permission I am
forwarding it to the list.
Redwood City, PSN
-------- Original Message --------
Subject: hurricane Dennis study
Date: Sun, 17 Jul 2005 12:11:05 -0400
From: Randall Peters
I have posted a paper to our server here at Mercer University Physics
that might be interesting to the amateur seismology community. It is
titled, "Correlation measurements of atmospheric pressure variations and
seismicity during hurricane Dennis", online at
The seismometer used for this study is an old Sprengnether that was once
part of the WWSSN. It was a gift from emeritus Prof. Deskin Shurbet of
Texas Tech University (my academic home before coming to Mercer). I've
noticed some discussions on psn concerning the viability of old surplused
instruments like this, which use the LaCoste zero-length spring. My opinion
is that they can be made to function very well indeed, with a modernized
sensor. In my case, the instrument works with an array form of the SDC
sensor. As opposed to the gap-varying mode of conventional commercial
seismometers used by professionals, the area-varying sensor has many
advantages. For example, I am presently operating without any force
feedback, although for the previous hurricane Charley study
I used the original coil/magnet (sensor/damper) subsystem as an actuator to
provide 'weak' force feedback. The feedback involved only a long-period
opamp integrator. The use of total force-balance (PID, or proportional
integral derivative network) is a cause for serious performance degradation
at low frequencies. I would like to encourage the amateur community to get
involved with me in studying the mHz frequency regime (where the earth
hums), by opening up instrument performance at low frequencies. To do so
requires a paradigm shift, and I suspect that the amateurs are more open to
this than are the professionals. One of the first things necessary is to
depart (heresy of heresies) from insisting on velocity detection. To take
the derivative is to ruin low frequency sensitivity, since as every student
that I teach knows-- it pulls out an 'omega' by the chain rule of
calculus--causing a 20 dB/decade falloff below the lower frequency cutoff.
If you look at the unfiltered earthquake record in the above referenced
paper concerning hurricane Dennis, you will see that the output from the
sensor is displacement, rather than velocity. For anybody insisting on
'doing business as usual', for better identifying P and S body waves; then
it is a simple matter to do post-processor numerical differentiation of the
filtered waveform. Incidently, for those who may be interested, I've posted
a paper that shows how to do filtering with excel:
The beauty of better low frequency performance is that you can study the
long-period Rayleigh and Love waves also with the same instrument.
And although many are suspicious of my claims, I am confident that my
Sprengnether is picking up eigenmodes (free oscillations of the earth).
Many of my own successes have been the indirect consequence of the amateur
community. For example, were it not for John Lahr and his interaction with
a broad group of individuals to include the amateurs, I would not have
learned of the Dataq software that I have found to be so powerful. Also,
Chris Chapman, who contributes regularly to psn discussions is a friend
whose expertise I admire and whose suggestions (and corrections) directed
toward various parts of my work have been greatly appreciated.
Additionally, Allan Coleman has just built an interesting broadband vertical
seismometer using a gap-varying form of my SDC sensor with a Willmore
Bottom line--don't ever underestimate the significance of what you've about!
I have been reluctant to get involved with psn before now for reasons
expressed in one of Chris' writings sometime back. He noted that academics
like myself get caught up so thoroughly in bureaucratic issues that they
barely have time to do the research that is expected of them.
In the event that I get more feedback (emails) from this communication
than I can completely respond to personally , please don't be offended. I
despise the treatment of 'kill by silence' that has been directed at me
because of my unconventional ideas.
Perhaps folks will be interested to know about the 'affordable
earthquake detector' that I am trying with some partners to bring to market.
There was an article about this in Popular Science (April issue, page 104).
I have developed a truly inexpensive autozeroeing electronics package to
work with the SDC sensors. Used it, in fact, to
operate the pressure sensor in the Dennis study. The board has only
three chips, each of which is less than $1 apiece. Doubt that this scheme,
which works with diodes, is able to do the low frequency measurements I've
mentioned; but it certainly would be an interesting possibility for a
bare-bones vertical instrument with outstanding performance. Maybe there
are some individuals who would like to try and build something using this
electronics with my compound vertical seismometer, described at
Would like to finally mention that Analog Devices has just marketed a
24-bit ADC that should work with my sensor directly and which sells for less
http://www.analog.com/en/prod/0,2877,AD7745,00.html (Tim Long at Georgia
Tech, just-retired seismologist alerted me to this chip; Tim is interested
in putting cheap but functional instruments in the hands of science
teachers; a great idea for which I hope we all can help!) Only problem is
that this chip requires a microcontroller to work.
Anybody with dsp experience interested in developing the necessary software
tools to make this happen with a cheap microcontroller? I can envision
something that might make the professionals take notice even if the price
were a hundred times greater!!
Keep up the good work,
Randall Peters, PhD
Professor and Chairman
Dept. of Physics
Macon, Georgia 31207
Public Seismic Network Mailing List (PSN-L)
Public Seismic Network Mailing List (PSN-L)
[ Top ]
[ Back ]
[ Home Page ]