Study On The Tomographic Inversion Technology Of The Tectonic Coal By The Airy-phase Of Seismic Channel Wave

The tectonic coal is material base of coal and gas outburst disasters,and it is an urgent problem to find an effective and feasible technology to identify the distribution of the tectonic coal in current coal mining.Based on the transmission method of channel wave seismic exploration,this study proposes the tomographic inversion technology of the tectonic coal on the Airy-phase of seismic channel wave.The travel time of the Airy-phase of the channel wave is picked up in this technology and then the tomographic inversion on it is carried out.Combined with the estimation of the velocity of the surrounding rock based on the time-distance features of the refraction wave,the velocity of the Airy-phase is fitted into the velocity of the shear wave in the coal seam,and thus the distribution of the tectonic coal is predicted.This study mainly includes the following three parts:The frequency dispersion equation of the channel wave is derived and the relationship between the group velocity and the phase velocity of the channel wave is obtained,and thus the hyperbolic time-distance features of the Airy-phase,the direct wave and the refraction wave are determined.It is believed that the transmission speed of the Airy-phase is the slowest and the energy is the strongest,and its speed is independent of the frequency of the channel wave and the thickness of the coal seam,only influenced by the velocity and density of the coal seam and the surrounding rock.The relationship between the velocity of the Airy-phase,the shear wave velocity of the coal seam and the shear wave velocity of the surrounding rock is discussed.Combined with the hyperbolic time-distance features of the refraction wave in the collected data,the velocity and the density of the surrounding rock are estimated.Thus the linear fitting relationship between the velocity of the Airy-phase and the shear wave velocity of the coal seam is determined,which is used as the theoretical basis for the identification of the tectonic coal according to the velocity of the Airy-phase.The method of the minimum travel time combined ray bending is used to inverse the velocity of the Airy-phase in the transmission method of channel wave seismic exploration,and the regularization factor is added to improve the stability of tomographic inversion.The influence of all parameters in the inversion are analyzed and the phenomenon that the cross-shaped velocity anomaly artifact will appear in the inversion results when the distribution of the tectonic coal is banded and paralleled to the roadway is found.And this kind of the artifacts could be eliminated only when the four-side observation system was arranged.Finally,the tomographic inversion technology of the tectonic coal by the Airy-phase of seismic channel wave is applied to the actual working face to predict the developing area of the tectonic coal.