One of the current research priorities in geophysics is the detection and tracking of dynamic changes in the Earth’s interior.As wave velocity and its variation are highly correlated with the physical properties and stress-strain of the medium,monitoring wave velocity variation is a common method to infer the dynamic changes of the medium.Effective monitoring of the dynamic changes of the medium is of great significance for cognition of nature,disaster prevention,and mitigation.In the field of non-destructive testing,real-time and high-precision monitoring of parameter signals that reflect structural characteristics can prevent catastrophic events and minimize damage.Therefore,it is of great scientific value and significance to find a high-precision medium change monitoring method.Coda waves,which propagate over longer distances compared to direct waves,provide multiple spatial samples within the medium and are highly sensitive to variations in medium properties.However,the application assumptions of current mainstream coda wave interferometry algorithms are more applicable to linear application scenarios,and the reliability cannot be guaranteed in the face of nonlinear medium change detection requirements.Although Dynamic Time Warping(DTW)algorithm introduced from the field of speech recognition has nonlinear analysis potential and has a certain ability to suppress cycle skipping,it is easily affected by the amplitude,resulting in low calculation accuracy.Furthermore,the algorithm has high time complexity.Therefore,based on this method,this paper proposes a dynamic coda wave interferometry with nonlinear analysis potential,high precision and high efficiency.The performance of this algorithm is compared with traditional coda wave interference analysis algorithms,primarily testing the accuracy,stability,and computational efficiency of estimating linear and nonlinear time delays.In order to more comprehensively study the applicability of the coda wave interferometry and supplement the application scenario research of the coda wave interferometry,different application scenarios will be constructed based on the numerical simulation method for research and analysis,including local medium changes and microstructure changes.At the same time,in order to test the effectiveness of coda wave interferometry in dealing with real coda signals,a concrete uniaxial stress test was designed and carried out to test the applicability of coda interferometry in processing real coda signals.The specific research is as follows:1.In response to issues such as excessive reliance on waveform amplitudes,inadequate utilization of waveform structural characteristics,and resulting low computational accuracy in traditional DTW methods,this study proposes a Dynamic Coda wave Interferometry.To address the dependency of waveform structural characteristics in cross-correlation processing,a pre-processing step is designed to enhance the computational accuracy.Furthermore,to overcome the low computational efficiency of the DTW method,an improved warping window is introduced,which significantly improves the computational efficiency while maintaining high precision.2.In the context of linear time delays varying scenarios,such as spatially uniform velocity changes,this study compares a new method with traditional coda wave interferometry,including Windowed Cross-Correlation,Stretching,and DTW methods using numerical simulation and artificially synthesized signals.The research focuses on the accuracy,noise robustness,spectral interference resistance,and computational efficiency of the algorithms.Additionally,a concrete uniaxial stress loading experiment is designed and conducted,where the aforementioned methods are applied to the experimental data.The relationship between the inferred velocity variations over propagation time,obtained using seismic interferometry,is used to reflect the stress loading conditions and is compared with the theoretical stress loading trend to assess the effectiveness of the method in practical applications.3.In the context of nonlinear time delays varying scenarios,this study further subdivides them into two categories: local medium variations and scattering microstructure variations.The corresponding application effects of seismic interferometry analysis in these scenarios are investigated using numerical simulation methods based on finite-difference modeling.In the scenario of local medium variations,two cases are considered: single-region and multi-region variations of local medium velocity.This study aims to comprehensively investigate the applicability of seismic interferometry in local medium variation scenarios.Three observables,including waveform distortion initiation time,decorrelation coefficient,and relative velocity changes,are employed to estimate the regions with local medium variations and determine the trends of velocity changes within these regions.In the scenario of scattering microstructure variations,the characteristics of the scattered wave signals are analyzed to investigate the potential of coda wave interferometry for detecting and localizing the migration of scatterers.The study aims to determine whether seismic interferometry can effectively identify the regions where scattering body migration occurs.4.Finally,for the seismic research scenario involving small variations in the source location,a source point displacement scenario is designed.Based on the observed distribution of time delays caused by changes in the source location,a source point tracking theory based on coda wave interferometry is proposed.Two spatial velocity distribution models are employed to validate the feasibility and effectiveness of the theory.Furthermore,the influence of co-located and non-co-located receiver point distributions on the source point tracking results is discussed for each velocity model.The aim is to investigate the impact of receiver point distributions on the accuracy of source point tracking.Simulation experiments demonstrate the practicality of the proposed source point tracking method based on code wave interferometry,expanding the application range of seismic interferometry. |