Charge to Students

Goals for Fall 2002 Semester

Seismometer Basics

Heiner Igel's Lectures on geophysics and Earth science:  http://www.geophysik.uni-muenchen.de/~igel/

A Good Summary of Pendulum Designs

B. H. Suits, Michigan Technological University:

Seismic Sensors and their Calibration

An advanced text by Erhard Wielandt

Latest version in MSWord Format
Earlier version in HTML

Wolfgang Lenhardt Lecture on

Seismological Instrumentation

E-mail Lists and Other Sources of Help

Public Seismic Network Mailing Lists and Archives:  http://www.seismicnet.com/maillist.html
(Reading the PSN archives and joining this list is strongly recommended!)

Info-EQ:  http://www.infoeq.it/forum/


Alan Jones' Web site with AmaSeis to display data from DATAQ DI-194RS AD: http://bingweb.binghamton.edu/~ajones/AmaSeis.html

Using a DATAQ DI-158U ADC with AmaSeis.

Bob McClure's Software

Randall Peters' FFT software page.

Earthquake Ground Motion

Ground motion amplitude and velocity as a function of distance, magnitude, and depth.  (Only works well with MSIE -- Not Firefox.)  Keep in mind that bacteria range from about 1 to 10 microns in diameter, while a human hair may be from 50 to 100 microns in diameter.

Graphs showing the distribution of "auto picks" from thousands of seismograms.  These are helpful in determining which phases are most easily seen.

Seismometer- and Harmonic Motion-Related Applets

First the equations: http://hyperphysics.phy-astr.gsu.edu/hbase/oscda.html

Compare damped and undamped motion: http://www.kettering.edu/~drussell/Demos/SHO/damp.html

Velocity response of a geophone with various damping ratios:



A good applet from Wolfgang Bauer, Michigan State University, for damped harmonic motion:  d.htm
He has posted this and many other applets for simple physical systems in his Applet Collection.

Damping:  What should the displacement look like if the pendulum is off set and then released?

One can see a graph of the displacement from a damped harmonic oscillator on this page.  The equations to keep in mind are (where mass = m, spring constant = k, and damping proportional to velocity = b):

Omega = (2Pi * frequency) = [sqrt(4mk - b**2)]/2m 

The damping factor =  b/ [2 sqrt(mk)] 

If the damping factor is zero (b = 0) then omega = sqrt(k/m) 

If the damping factor is 1 (b = 2 sqrt(mk) ) damping is critical and a displacement will return to zero exponentially. 

If the damping factor is greater than 1, displacement will return to zero at a slower exponential rate.

A damping factor of 0.7 to 0.8 is good for seismic instruments.  To see what 0.8 looks like, use the applet above and set m = k = 1 and b = 1.6. There is a very small overshoot and then a return essentially to zero.  For 0.7, set m = k = 1 and b = 1.4.

Given the observed amplitude of two successive peaks, the damping ration can be computed on this page.

Plots of pendulum response to ground motion.

Home-built Seismometers

Amplifier/Filter circuit (amateur)

Peter Roberts' circuit to boost the low-frequency response of a velocity sensor.

Larry Cochrane's Amplifier/Circuit (professional)

Davis Saum has posted his electronics schematics and he sells assembled units and kits.

Swinging Gate Boom-Length Considerations

Zero-length spring for a long-period vertical.

Improving a geophone to produce an affordable, broadband seismometer.  A Stanford University PhD thesis by Aaron Barzilai in pdf format (1.7 MB).  These appear to be slides from a talk on his thesis. 
Additional links to Aaron's geophone research at Stanford appear here:   http://micromachine.stanford.edu/smssl/projects/Geophones/

Bob McClure's horizontal ( relatively small, but with strong magnets) and vertical designs.

Especially good description of swinging gate (Lehman) system: http://users.viawest.net/~aloomis/seismom.htm

Folded pendulum: http://jclahr.com/science/psn/folded/

Inverted pendulum: http://jclahr.com/science/psn/inverted/



Handheld Seismometers


Garage-built Seismometer

Lehman Seismometer

Capacitive Sensor
    Randall Peters' technique

Karl Cunningham's Home-made Force Balance Accelerometer

Diamagnetic Suspension Seismometers


Silicon Micromachined Accelerometer/Seismometer

Hall Effect Sensor
    Chris Chapman's Design: http://mariottim.interfree.it/doc11_e.htm

Hall Effect, Diamagnetic, and other good ideas
    Meredith Lamb's Pages: http://geocities.com/meredithlamb/

Sean-Thomas Morrissey's STM-8 design: 

Inexpensive Seismic Equipment

David Saum's Inexpensive Seismometer Project

Larry Cochran's Public Seismic Network Supplies

Mauro Mariotti's Solutions
    http://www.infoeq.it  or the mirror:  http://mariottim.interfree.it/index_e.htm

Summary of Seismometers for Teaching and Research: http://quake.eas.gatech.edu/Instruments/InstrumentSurvey.htm

Demonstration Seismographs (Although these were designed to illustrate how a seismic sensor works they do provide a possible starting point for a working system.): http://quake.eas.gatech.edu/Instruments/LPVERT0.htm

Professional Seismic Sensors

ORFEUS web site with links to many sensors and approximate prices for many of them.

Guralp Broadband Force Feedback: http://www.guralp.net /

Summary of a Range of Seismic Instruments by Tim Long at Georgia Tech

Sources of Analog-to-Digital (AD) Converters

$25 DATAQ DI-194RS: http://dataq.com/194.htm
See this page for more information on the DATAQ AD's.

Randall Peters' Game Port AD: http://arxiv.org/html/physics/0202023 

Sources of Magnets

Sources of Hardware

K&K Surplus

Sources of Electronic Components and Ideas

Sensors Magazine:  http://www.sensorsmag.com/

Chip Center:  http://www.chipcenter.com/

Educational Seismograph Networks

US Educational Seismograph Network (With links to most US networks):  http://www.indiana.edu/~usesn/

Georgia Educational Seismograph Network (Tim Long): http://quake.eas.gatech.edu/teachnet/GaESNnetwork.htm

Italian Experimental Seismic Network Sites

Friuli Experimental Seismic Network

Seismo Surfing