Influence of Soil State on Characteristics of Seismic Signals from Moving Objects

The paper presents studies to establish the influence of soils state on characteristics of seismic signals from moving objects. The effect of ground temperature and moisture on the passage of seismic waves is considered. It is shown that surface waves, which are used to detect moving objects, are characterized by the same propagation effects in soils as body seismic waves. It has been established that an increase in ground moisture in its effect on seismic signal characteristics is equivalent to an increase in absorption coefficient of soil. This leads to a greater attenuation of seismic signal and, accordingly, to a decrease in the detection range of moving objects by seismic devices and systems.

I. Introduction

When various objects (people, animals, vehicles) move on the earth surface, their forceful impact on the ground occurs, resulting in two types of seismic vibrations in the ground: body waves and surface waves. It is known [1] that a decrease in displacement amplitudes of surface waves caused by the divergence of its front is proportional to √ R, where R is a distance to an oscillation source. And in the case of body wave, a similar decrease is proportional to R. This causes surface waves to appear stronger at the earth surface than body waves when moving away from the source. It is also known that the contribution of Rayleigh surface wave to the distribution of energies between different types of waves in a near-surface layer is decisive: Rayleigh wave account for about 70% of the energy of surface waves [1]. Therefore, when the objects moving on the ground are detected by seismic devices (systems), their transducers register precisely the Rayleigh seismic surface waves.