I wanted to achieve a sensitivity limited by microseisms and other sources of background noise. For distant earthquakes it is necessary to have sensitivity to displacements over 20 - 30 second period and I aimed to get a resonant period for the sensor of at least 5 seconds.
The eventual sensor came out at a total cost of around $2, given that some of the parts I already owned and some were donated. Starting from scratch it should cost no more than $20. No machining or special tools were to be needed. The eventual design can be built in less than an hour and things are held together by glue and magnets. The bulk of the time was consumed in finding the right parts. This only covers the sensor - the hardware to convert the analogue signal to digital form, record it on a computer and do signal processing to recover useful seismic signals constitutes an additional cost. Fortunately, I had all the elements for this already at hand.
 | Drumplot - record of the last 24 hours of data, filtered for distant quakes, in one plot |
| Raw - last 24 hours unfiltered |
| Calexico (California - Mexico Border) 2/22/2002 M5.7 - Drumplot of day also showing M3.9 & 3.3 Aftershocks |
| Hindu Kush 3/3/2002 M7.4 - Overall record and first few minutes with phases |
| Beverly Hills 3/3/2002, M1.7 - A local microquake |
| Mindanao, The Philippines 3/5/2002, M7.5 |
| Honshu, Japan 3/10/2002, M5.8 - Just Detectable |
| Santa Barbara 3/16/2002, M4.6 |
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| Building tilts as cars enter and leave garage |
| Effect of high winds |
| ForceField Magnets for generously providing the cylindrical NIB magnets |
| Meredith Lamb whose website suggested the arrangement of cylindrical magnets for stable levitation. |
| Spectroscopic grade graphite rod: Ted Pella Inc. Cat. # 61-15. Experiments showed that "leads" for propelling pencils, at least the batch I bought, were also highly diamagnetic. I glued a stack together with super-glue to give a satisfactory substitute. |
| Cadmium Suphide cell: Radio Shack (pack of 5 for around $2.49) |
| Diametrically magnetised cylindrical magnets: ForceField The units I used are unfortunately not currently available. |
| HP/Agilent for E1326B DMM and HP 75000 E1301A VXI chassis |
| Live Internet Seismic Server - near real-time seismograms from worldwide stations |
| Near Real-Time List of Major Earthquakes - USGS |
| Recent Earthquakes near LA |
| Recent Earthquakes in all of California |
Last updated 08/30/02