GEOPHONES AND DIGITAL FREQUENCY CORRECTION: ASSESSMENT OF APPLICABILITY IN SEISMOLOGY
P.A. Dergach1, A.A. Duchkov1, S.V. Yaskevich1
1Trofimuk Institute of Petroleum Geology and Geophysics of SB RAS, Novosibirsk, Russia
Keywords: Earthquakes, seismology, local and regional networks, seismic monitoring, geophone, electrodynamic seismometer, natural frequency, frequency correction, low-frequency deconvolution, digitizer, amplifier noise.
Abstract
Monitoring tasks often require the installation of temporary or local densification of existing seismic networks. The high cost of standard broadband seismometers limits the possibilities of increasing the number of stations. An alternative is to replace them completely or partially with more low-cost seismic exploration geophones with the expansion of the recording frequency range by low-frequency deconvolution. A methodology is proposed for assessing the applicability of geophone-recorder equipment sets for seismological monitoring tasks based on measurements of the recorder's hardware noise and the passport characteristics of the geophone sensor. It is shown that only the use of modern low-noise recorders and low-frequency geophones provides sufficient sensitivity for monitoring local and regional seismicity. A new method has also been proposed for determining the maximum allowable value for frequency correction of recording a specific earthquake (for this, the amplitude-frequency response of recording the recorder's hardware noise and recording after deconvolution are iteratively compared). It turns out that the more intense the earthquake, the more effective is the expansion of its recording spectrum. Using the example of recording the Kolyvan earthquake (M =4.3, epicentral distance of 30 km), the possibility of restoring the recording spectrum to 0.3 Hz for a geophone with a natural frequency of 4.5 Hz is shown. Due to this, the signal amplitude increased by more than 3 times, and the process of identifying phases and determining the arrival times of target waves was significantly simplified. It is shown how, using the seismic mode at the location of the proposed network installation, it is possible to assess whether the earthquake records produced by the proposed kit will be distorted and to determine its applicability in advance. The method has been tested using the example of equipment selection and data processing of a temporary seismological network in the Lena River delta.
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