Abstract:Microtremor, also known as microseism and ambient noise, refers to the tiny vibration of the earth. Its amplitudes range from about a few to a few hundred microns, and its frequencies range from about a few seconds to tens of Hz. Generally, microseisms refer to the low frequency waves produced by wind and ocean waves, whereas microtremors refer to high frequency waves created by mechanical vibration excitation, the boundary of which is about 1 Hz. The microtremor wave field is a complex time-varying field, and its main ingredient is the fundamental mode of the surface wave, a small amount of body wave, and high order surface wave. Fundamental mode Rayleigh waves dominates the vertical component, whereas Love waves dominate the horizontal component. Shear wave velocity structure is an important index for site condition and is considered an engineering site classification. Convenient and economic field near-surface velocity structure exploration methods have been the focus of research in the field of engineering seismic exploration. In the seismic active fault evaluation of near fault strong ground motion, a 3D underground structure model must first be established. Artificial or natural seismic exploration methods cannot meet the requirements, and some sites are also limited by existing buildings, deployment difficulties, and low resolution for the surface velocity structure. Meanwhile, blasting as a means of seismic exploration in urban areas have received increasingly less public acceptance. The drilling method is the most direct method to determine the soil ground velocity structure and soil dynamics parameters, but the high cost and limited drilling depth restrict its large-scale use. Compared with the above method, the Rayleigh surface wave method is economical, simple, and convenient; it has unique advantages in solving the abovementioned problem. Based on the generation of the Rayleigh wave signal as well as the collection and analysis methods, the surface wave method can be classified into two types: active detection method (SASW, MASW) and passive method (Spatial Autocorrelation Coefficient (SPAC), F-K). The microtremor survey method involves many steps and subjective judgment, and entails the necessary pre-processing of data, post-processing of the dispersion curves, and rapid on-site assessment tools for array. In order to facilitate technical engineering use, developing a visualization analysis software system is necessary. According to the need of microtremor data processing, we developed the software system (MSM-SPAC) for the SPAC microtremor survey method. The main functions include the design of the observation array, the azimuth distribution analysis of the array, data format conversion, selection of the effective interval of observation data, data signal filtering, re-sampling, SPAC coefficient parameter calculation, dispersion curve extraction, editing, merging, and project management. The software is user-friendly and easy to operate.
