Real-Time Calibration of Velocimeters Using a Reference Standard

Abstract

All digital seismic recorders of the Crimean seismological network are equipped with sensors inherited from galvanometric recording. Long-term channels are equipped with SKD sensors, and shortterm channels are equipped with SM3, SKM, SKH, and S-5-S sensors. The instruments periodically undergo preventive maintenance due to wear and long operation life. There are no equipment specialists at peripheral stations. All necessary installation, preventive maintenance, adjustment, and calibration work is done by specialists from the Institute of Seismology and Geodynamics’ hardware and software support team during business trips. In this regard, an urgent need arose for the real-time control of velocimeter parameters and the entire end-to-end measuring and recording channel. Experience at peripheral seismic stations and temporary seismic observation points not equipped with shaking tables has demonstrates the convenience of calibrating short-term seismic channels using a reference standard calibrated mobile digital seismic station. This station is assembled based on a Baikal-8 digital seismic recorder and SK1-P three-component sensor. The reference standard is precalibrated on the shaking table located at the Simferopol seismic station. The paper describes the calibration of the reference standard on a shaking table and different approaches to calculating the main parameters of a velocimeter. The relationship is obtained between the main parameters of the velocimeter and the extremum times and zeros of the velocimeter response function to a displacement step. It is possible to control the velocimeter parameters in real time the obtained formulas, even in the field using. Of special note is the idea of calibrating seismometric channels with respect to the reference standard, which can be implemented without forced external actions. A new method for calibrating a digital seismic station using a reference standard is described, based on analysis of the ratio of microseismic background spectra. The parameters of the calibrated station are determined using synchronous recording of the microseismic background and the mathematical optimization package in OriginLab software. The formulas for calculating velocimeter parameters using a standard are given, which make it possible to determine the complex frequency response of the digital station. This is a convenient method because it is real-time and calibration does not require laboratory conditions, the use of microseisms, or the ability to determine all parameters of endto- end measuring and recording channels simultaneously.