Microtremor Semi-Wavelength Inversion Imaging Based on Spectrum Optimization Technology and Its Application

This study integrates the Extended Spatial Auto-Correlation (ESPAC) method, the Multi-Window Stacking Method (MWSM), and half-wavelength inversion imaging to construct a microtremor survey methodology to address the exploration requirements for deep fractured geothermal resources. The system enhances the detection accuracy of deep geothermal reservoir structures through synergistic innovation in core algorithms and standardized field procedures. The methodological innovation is demonstrated by: employing the MWSM strategy to overcome the limitations of traditional single time-window processing, utilizing a dual time-window cooperative mechanism to achieve an optimal balance between high-frequency noise resistance in shallow sections and low-frequency convergence in deep sections, thereby significantly enhancing full-band signal continuity; and effectively suppressing complex environmental interference by combining standardized techniques such as cross-shaped array configuration, precise station positioning, and rigorous sensor coupling. In the application to a geothermal target area in Xinyu, Jiangxi Province, the system identified multiple heat-controlling faults and several target low-velocity anomaly zones. Key geological features revealed include deep low-velocity fault channels and medium-shallow vuggy limestone geothermal reservoir cores. Typical targets were strictly verified by drilling: the prediction error for the top boundary depth of the geothermal reservoir was less than 3%; the locations of fault zones and the spatial distribution of the reservoirs showed high consistency with the velocity profiles. Drilling revealed that the vertical control depth of the fault system reaches nearly a kilometer, confirming that the three-dimensional delineation capability of this method for reservoir structures and permeable channels meets engineering accuracy requirements. The research results provide reliable technical support for the exploration of deep fractured geothermal resources.