Seismic instruments: article

Instrumental schemes for extending geophone frequency characteristics
Sadovsky Institute of Geospheres Dynamics of Russian Academy of Sciences
Journal: Seismic instruments
Tome: 55
Number: 3
Year: 2019
Pages: 5-23
UDK: 550.34.03
DOI: 10.21455/si2019.3-1
Аnnotation file
Bibliographic list
Keywords: geophone, amplitude-frequency characteristic, instrumental diagram, negative resistance, attenuation, transfer function
Аnnotation: Solving engineering problems often requires the recording of signals in the 0.1-2000 Hz range. The low limit of this range is beyond typical frequency ranges of geophones, which are usually inexpensive and easily installed. Here we attempted to extend geophone frequency characteristics by multiplying the transfer functions or overdamping by negative impedance. The limits of applicability of these methods were estimated. The upper limit of the velocity recorded by a geophone is determined by the gap in which the coil shifts relative to the sensor frame. The lower limit is dependent on the total hardware noise.The Brownian noise of a mechanical oscillatory system and the noise of the measuring scheme of the channel are the principal contributors to the hardware noise. A prototype device was constructedon the base of multiplying the transfer functions. Using laboratory measurements on a shaking table and microseismic noise records, we found that the modified geophone works as a sensor with a naturalfrequency of 2 Hz. This value depends on the microseismic characteristics of the site where the device is installed. Field experiments were held near an active mine, and we were able to detect mine bursts and career explosions in the frequency range down to 2 Hz. Therefore, we conclude that the modified geophone fits the requirements for monitoring local and regional seismicity as an analog of a short-period seismometer.