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Monday, January 11, 2010

Ears and hearing: so you want subbass, don't you?!?


Design and Application of an Electromagnetic Vibrator Seismic Source
Seth S. Haines (Geophysics Department, Stanford University, Stanford, Calif. 94305 E-mail: shaines@usgs.gov)


Vibrational seismic sources frequently provide a higher-frequency seismic wavelet (and therefore better resolution) than other sources, and can provide a superior signal-to-noise ratio in many settings. However, they are often prohibitively expensive for lower-budget shallow surveys. In order to address this problem, I designed and built a simple but effective vibrator source for about one thousand dollars. The "EMvibe" is an inexpensive electromagnetic vibrator that can be built with easy-to-machine parts and off-the-shelf electronics. It can repeatably produce pulse and frequency-sweep signals in the range of 5 to 650 Hz, and provides sufficient energy for recording at offsets up to 20 m. Analysis of frequency spectra show that the EMvibe provides a broader frequency range than the sledgehammer at offsets up to ~10 m in data collected at a site with soft sediments in the upper several meters. The EMvibe offers a high-resolution alternative to the sledgehammer for shallow surveys. It is well-suited to teaching applications, and to surveys requiring a precisely-repeatable source signature.

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