Shallow seismic sounding based on ellipticity analysis of microtremor

Abstract

A brief review is carried out of the previous study about the spectral ratios of horizontal and vertical components of microseismic oscillations displacement. The basic principles of resonant boundaries allocation and the construction of deep sections based on the H/V relations (ellipticity) are considered. A description of the equipment used, the method of recording and processing microseismic noise are presented. The main goal of the research work is to clarify the nature of the connection between the ellipticity of microseisms with geological features and the correctness of constructing deep sections based on them. The initial data are the amplitude spectra of the components of microseismic signal, obtained using the fast Fourier transformation. In the course of experimental work it was found that the spectral relations retain their characteristic features regardless of the azimuth of observations. A number of practical examples compare microseismic sections with results from other geophysical methods and drilling information. The results obtained indicate the complex nature of the ellipticity of microseismic noise under different conditions, however, they make it possible to determine the main interfaces between the upper part of the geological section. Resonant boundaries emitted by microtremor are often located near refractive seismic boundaries. This is consistent with the theory that resonance effects occur at the interface between two media with a high contrast of acoustic impedance.