Effect of frequency content of seismic source load on Rayleigh and P waves in soil media with cavity

Abstract

Subsurface characterization has always been an interesting issue in Geotechnical and geological engineering, especially when there is a potential risk of subsurface anomalies such as cavities and sinkholes. Due to the low resolution and accuracy of seismic recorded data at higher depths, anomalies identification has become more difficult. In this paper, the effect of various types of seismic source loads such as hammer impact, short-time impact, sinusoidal source and Ricker wavelet with a peak frequency of 100, 50 and 20 Hz is evaluated to identify the subsurface cavities by using the Finite Element Method in Abaqus 6.14 software. In addition, The ability of R and P waves are compared after the filtering the waves to detect cavities at different depths of 2, 6, 10 and 20 m. The results show that the frequency content and peak frequency of source load have a significant effect on the penetration depth and wave field resolution. Furthermore, filtering methods and separating R and P waves could be more helpful to identify the shallow and high depths cavities. Also, Ricker seismic source with a central frequency of 100 Hz, hammer impact and short-time impact indicate suitable results for cavities located at depths of 2, 6 and 10 meters. Whereas, it is difficult to identify the backscattered R waves from the cavity at the depth of 20 meters. However, low-frequency seismic load, such as 20 Hz Ricker source load, provides backscattered R and P waves from the cavity at the depth of 20 m. In general, the acceptable results can be obtained by using a combination of P and R waves and applying seismic load proportional to the depth of identification.

Keywords

• cavity
• seismic source load
• frequency content
• rayleigh wave
• p-waves
• wave field