Review on key factors of microseismic source spectrum calculation in geotechnic engineering

Microseismic monitoring is widely used in the analysis of engineering disasters such as mines and tunnels, all of which are based on microseismic source parameters. The calculation of microseismic source spectrum is the basis of source parameter calculation. Once the source spectrum is determined, most of the source parameters can be calculated accordingly. However, research into the calculation process and method of microseismic source spectra is limited. Therefore, we investigated the basic steps and methods of microseismic source spectrum calculation in detail. This includes four main steps: waveform processing and source location; signal spectrum calculation; signal spectrum correction and source spectrum determination. Signal processing involves removing the instrument response, filtering and arrival picking with localisation to provide basic parameters for subsequent calculations. Signal spectrum calculation involves not only common methods such as the discrete Fourier transform, but also the lag-window spectral technique and multi-taper methods. Signal spectrum correction involves geometric spreading, site effects, and attenuation, which are all influenced by multiple and complex factors. Source spectrum determination initially requires the theoretical source spectrum model to be determined, followed by the selection of the objective function and fitting method. This study briefly analyses the impact of these factors on the calculation of the microseismic source spectrum and suggests possible future research directions. These results can be used as a reference for calculating the source spectrum, thereby establishing a foundation for calculating source parameters and ultimately providing theoretical support for standardising and normalising engineering microseismic monitoring and the quantitative warning of engineering disasters.