The application of variable‐frequency directional seismic wave technology under complex geological conditions

Abstract

Monofrequency directional seismic wave technology can be used to manipulate the phases of seismic waves, thereby focusing seismic signals into beams and strengthening the energy in the main beam direction. However, it is unknown whether a variable‐frequency signal can form a directional seismic wave, and the applicable conditions for utilizing this technology have not yet been reported. In this paper, we analysed the variable‐frequency directional seismic wave theory and methodology through ray tracing and the seismic wave equation. Based on the variable‐frequency directional seismic wave principle, the effects of directional parameters on the main beam direction and half‐power beamwidth were discussed in detail. In addition, the effectiveness of the variable‐frequency directional seismic wave method in several complicated velocity models was discussed. Numerical tests with the variable‐frequency directional seismic wave technique indicated that the energy intensity in the main beam direction increased by two to six times and the signal‐to‐noise ratio of the targets signal increased by 0.60–0.84 dB. Additionally, we used variable‐frequency directional seismic wave technology to analyse a shallow geological structure with a 9‐vibrator array in an area of Jilin Province. The field experiment results revealed that the near‐surface exploration depth increased from 60 to 240 m. Therefore, under complex geological conditions, the variable‐frequency directional seismic wave technology can improve the target signal at little cost.