research-grade instruments are carefully designed,
meticulously constructed, and cost many thousands of dollars to
purchase and install,
a simple seismometer is neither complicated nor expensive to
and offers the amateur observer an amazing and fascinating view of the
earth's seismic activity.
amateurs start with a horizontal-sensitive instrument built on a
"garden gate" principle. Many
hundreds of variations on this basic principle have been implemented in
sensors built by amateurs all over the world
"Lehman" horizontal seismometer (designed by James D. Lehman of James
Madison University in
Harrisonburg,VA) is popular among the amateur
seismologist community, and is easy to construct and operate, while
still providing a sensitivity suitable for
to moderate intensity events the world over. This
instrument was first
described in an "Amateur Scientist" magazine article in
the July 1979
Scientific American magazine. Go
to http://seismicnet.com/lehmntxt.html to read a
copy of the original
Scientic American magazine Lehman seismometer article.
Several articles for constructing this type of horizontal seismometer
can be found with an Internet search
on the words "Lehman" and "Seismometer" in your favorite search engine. One such construction
article for a Lehman seismometer design can be found at http://seismicnet.com/lehman_manual.pdf
TC1 is a vertical seismometer with a natural period of approximately 1 second. Open-source hardware - based on the Arduino Uno
- boosts the longer periods in its recordings, so that teleseismic earthquakes
are routinely detected, in addition to regional seismic activity. Because of
its robust design and affordability, it is ideally suited for any classroom.
plans for the TC1 and the interface between sensor and computer are freely available online to build your own, but the TC1 can also be purchased as a kit. Further information is available at http://tc1seismometer.wordpress.com.
One of the seismometers in operation at AlabamaQuake is the
Shackleford-Gundersen (S-G) horizontal-sensing instrument,
the design for which is based on a September
1975 article in
the "Scientific American" magazine sub-titled, "Electronic
stratagems are the key to making a sensitive seismometer." The instrument
was developed by Barry Shackleford and Jim Gundersen, and has been built in many variations over the years by amateurs around
The SG seismometer design includes somewhat more complex
amplification and filtering electronics,
and while not calibrated in its response, does nonetheless
offer a moderately long-period response to
surface seismic waves associated with earthquakes.
It requires a smaller physical footprint that the Lehman horizontal
sensor design, and hence requires
a smaller thermal isolating cover. As it is based on a
vertical-hanging pendumum instead of the horizontal "garden-gate"
pendulum, it requires less attention to periodic leveling
adjustments to maintain its alignment. The
original Scientific American magazine article
with plans for building the S-G horizontal seismometer can be found at http://seismicnet.com/sgsensor.html along
with modifications and design improvements developed by Larry Cochrane in
his Redwood City SG Seismometer unit.
Go to http://seismicnet.com for more seismograph
plans, equipment, and software, and links to other sources.
advanced seismometer, and another of the instruments in
operation at the Alabamaquake
seismic station in Huntsville, is the Inyo Force-Balance
Broadband Vertical (FBV) seismometer
designed by David F. Nelson and Brett M. Nordgren.
This instrument offers a broadband response, flat to velocity
between 30 Hz and 50 seconds,
and a calibrated sensitivity with both low-gain and high-gain
The Inyo design, and that of two successor instrument designs, has been
offered for construction
and use by advanced amateurs the world over. The designs have
been replicated and installed
by a small group of interested builders, and have proven quite
successful in delivering a broadband
seismometer performance on par with commercial instruments costing much
calibrated performance of the Inyo seismometer is attained through the
use of a closed-loop
feedback system that applies a correcting force to the seismometer's
suspended mass to counteract
any displacement of that mass caused by a seismic input to the
The electronic circuitry used in this feedback system is described at http://bnordgren.org/seismo/FBV/FBV_Circuit_Description.pdf.