Simple calibration of geophones using an audio source

We develop a new methodology to calibrate geophones based on audio sources. A suitable low-frequency loudspeaker reproduces a frequency sweep, it is sensed by the geophone and then it is recorded by a seismograph. The recording is then transformed to the frequency space and compared with a reference frequency response. Although this procedure is not intended for rigorous calibrations, it is a cheap and fast alternative to the common calibration methods (vibrating table and calibration current) intended for the detection of anomalous geophones. This study presents the results of the application of the proposed methodology to two different types of vertical component geophones. The frequency response of each particular geophone is limited within 20% of the mean response for the lower frequencies considered. Better results can be obtained by taking a larger number of measurements for each geophone and by carefully controlling its inclination.