Optimization of seismic data processing flow for tunnel detection usingenergy spectrum and stacking spectral energy peaks of overlapping arrays

摘要

Analyses of seismic data demonstrate increasing acoustic energy recorded above an underground tunnel. This is attributed to internal reverberations within the tunnel, reflection (backscattering), and wave conversion. Soil heterogeneity, changes in geophone-to-ground coupling and the shape of the generated signal introduce fluctuations into the trace spectrum. Overlapping common-shot arrays, with shot-to-shot intervals (along linear traverses) were analyzed. The data processing flow was optimized to statistically improve positioning of the most regular energy maxima along each traverse. Corrected for divergence, the single-shot data were filtered to remove spurious-frequency spikes caused by geophones tilt and instrumental noise. A median filter was applied to the energy spectrum function of each record to filter out random anomalies generated by poor geophone planting. Single record spectral energy functions were transformed to the weighted functions, where the similar weight value was assigned to each energy peak. Single shot weighted functions were stacked (summed) to identify the spectral energy peaks distribution along the traverse. Summing the weighted common shot energy functions within the window decreases the influence of geophone positioning errors. Processing of experimental data showed good correlation of the known tunnel position and main maximum of the stacked energy function.