Seismic Detection Of Goafs In Urban Coalfield

With the development of the society,more and more attention is paid to the safety of urban construction,and the understanding of underground structure is an important part of urban safety construction.The mined-out areas of the coal field in the city refers to the narrow and long space filled with sparse material after the coal seam is mined.Its thickness is generally small,but it adds hidden dangers to urban construction.The application of geophysical methods,especially seismic methods with higher resolution,to identify mined-out areas is an important research direction of urban geophysics.In this paper,the forward simulation method is used to analyze the identification characteristics of the mined-out area on the seismic profile,and the high-frequency reconstruction method based on complex cepstrum calculation is used to improve the resolution of the seismic profile.In the forward calculation research,this paper systematically summarizes the key issues of the forward calculation of the acoustic wave equation,including difference accuracy,stability analysis,numerical dispersion,boundary conditions,etc.,which provides a basis for the forward modeling of the mined-out area.Because the filled sparse material has the characteristics of low velocity,in the mined-out area forward calculation,random velocity will be used to simulate the mined-out area.The low-velocity medium has the phenomenon of in-phase pull-down in the imaging section,especially in the high-frequency section.To be obvious,this is also a direct sign to identify the mined-out area.In the study of high-frequency reconstruction methods,this paper proposes a high-frequency reconstruction method based on cepstrum calculation.By using cepstrum calculation to replace the amplitude spectrum of the original data and keep the phase spectrum unchanged,the frequency bandwidth of seismic data can be increased to achieve the improvement.The effect of seismic resolution,and the correctness of the method is verified by the model.In this paper,combined with forward calculation and high-frequency reconstruction methods,the characteristics of seismic imaging in the mined-out area are studied,and they are applied in Jinan,Shandong.The method was verified using data from a certain area of Jinan.The collected data was processed with conventional seismic data and the frequency was increased.Through the display of drilling information,the identification features of the mined-out area based on the pull-down feature of the event axis were more obvious,which proved the effectiveness of this method.