Chapter 1.3 - Active vibromonitoring: experimental systems and fieldwork results

Abstract

This chapter presents results of fieldwork on active seismology in the Altay-Sayan and Baikal regions. Experiments with powerful low-frequency vibrators have been carried out in the Altay-Sayan region for determination of the sensitivity of the active vibroseismic monitoring system to small changes in the seismic waves velocities in the Earth’s crust. It has investigated the influence of the Earth’s crust tidal deformations (having the order of 10−7) on amplitude-phase characteristics of the seismic waves radiated by the vibrator. Three-component recording systems were located at a distance of 356km from a 100-tons force seismic vibrator. The radiation sessions of harmonic and sweep signals were repeated every 3hours over 8 days. This made it possible to obtain the time series of variations in the amplitudes and phases of the recorded signals and wave arrival times. Both 12 and 24-hour periodicities correlated with the Earth’s tides were found in the spectrum of variations of the recorded signals. This experiment has shown that the active monitoring system makes it possible to detect relative variations of the seismic wave velocities of the order of 10−5–10−6 in an area of 300–400km around the source and to carry out direct monitoring of the state of stresses in this area for detection regions and phases of the critical stress as an earthquake precursor. The geotechnology for investigation and verification of the Earth’s crust velocity models using mathematical simulation and active seismology methods are presented. Implementation of the technology for two velocity models of Earth’s crust for the south of the Baikal rift zone and adjacent Mongolian areas in experiments called Baikal Explosion Seismic Transect and Program for the Array Seismic Study of Continental Lithosphere is considered. The Internet resource of the information technology is implemented as part of the scientific information system “Active Seismology.”