Synchronization system of stations records for Mikhnevo small aperture array

The small-aperture seismic array (SSA) operating in the seismic observatory of the Institute of Geosphere Dynamics, Russian Academy of Sciences (IGD RAS) in Mikhnevo allows establishment of spatial and timing distribution of seismic events with a magnitude of M = 1.5 and higher. In the course of its exploitation, we revealed the disadvantages of the synchronization system of seismic stations, which led to mismatches of seismic records both with astronomic time and between the channels of different analog-to-digital converters (ADCs). The complex of hardware-software tools was worked out in order to enlarge the reliability of the system and to provide its correspondence to the requirements of the SSA modernization. By the signals of the GPS receiver, the minute marker driver generates the pulses whose rising edges precisely coincide with the beginning of every minute of astronomic time. In addition to the main functions, the RS-485/RS-232 transmitter-receiver transforms these pulses into a serial code and passes it to the remote seismic station via the digital communication line. A specially designed COM-port switch receives the data from seismic stations and directs them to the computer in a single stream. Each data fragment from different channels is recorded in the common file as it proceeds to the switch inputs, which completely excludes the time mismatch between the records.     

Means of synchronization of independent seismic stations in seismic arrays

Basic reasons for different kinds of failures of record synchronization of the independent seismic stations, operating as elements both of domestic and foreign seismic arrays, are established. Proceeding from it, software and hardware are proposed for ensuring reliable and precise synchronization of stations. Their operation is based on periodic fine tuning of the station’s analog-to-digital converter (ADC) sampling cycle by an exact time signal obtained from the GPS receiver. This procedure is executed with minimum or even no additional load on the controller of the seismic recorder. Such an approach allows not only matching each ADC sample to astronomical time, but also to provide simultaneous ADC sampling of all stations in the seismic array with an accuracy of 10 μs, which is especially important for solving a number of geophysical problems. Experimental researches and trial operation of the created equipment are carried out. High reliability of the equipment and compliance of technical characteristics to the purposes of the development are confirmed.