Summary
To study the characteristics of the scattering seismic waves in random heterogeneous media, especially the incoherent coda waves only caused by the multiple scattering, we carried out the laboratory experiments on samples of glassbeads and epoxy mixture without porosity and obtained the transmitted wavefields. The coherent and incoherent waves decomposed from the transmitted wavefields are analyzed. The results prove that multiple scattering causes a decrease of high frequency components of the direct wave and the attenuation of direct waves. Also, the incoherent coda waves induced by multiple scattering is a non-stationary signal. In the conventional seismic exploration, the incoherent scattered waves are usually regarded as noises. The result will have its application in the seismic de-noising.
Introduction
The earth’s interior is heterogeneous, and the heterogeneities can be separated into long-wavelength heterogeneities and short-wavelength heterogeneities (Sato and Fehler, 1998). The media containing small-scale heterogeneities are referred to as random media, and their scale sizes are smaller than the resolutions of conventional seismic method. Multiple scattering occurs when the seismic wave propagates through random media. Multiple scattering in random heterogeneities causes the variations in velocity (e.g. Mukerji et al., 1995), and variations in waveforms and amplitudes across seismic arrays (e.g. Ringdal and Husebye, 1982), producing apparent attenuation with distance (e.g. Richards and Menke, 1983). The incoherent waves generated by multiple scattering results in the ‘Seismic Coda’ which forms the tail of the seismograms (Aki, 1975). In the conventional seismic exploration, the incoherent scattered waves are usually regarded as noises. However, the noise is site dependent and is not the same as the noise that randomly appears in the time-series (Scales and Snieder, 1998). This is important for seismic data processing but not well recognized in the field of seismology and seismic explorations.
