Research On Application Of Transient Rayleigh Wave In Buried Fault Detection

In shallow reflection prospecting, the effective reflection information near the sourcewill always be interfered by surface wave which has a strong energy, so we can't getthe velocity information of shallow layers. Based on this characteristic we try totransform surface wave from noise to signal, then use it to get the velocity structure ofblind zone in detection. By improving Rayleigh wave's data acquisition and dataprocessing technical, put it in use of detecting shallow velocity structure's horizontalvariation near buried fault.This paper states the basic principle of Rayleigh wave, depicts its advancements homeand abroad. There are two main Rayleigh wave exploration methods: spectral analysisof surface wave (SASW) and multi-channel analysis of surface wave (MASW). In thepaper the two methods' advantages and disadvantages are researched, considering thecharacteristic of media's horizontal large variation near buried fault, SASW andMASW combined processing method is put forward. Many different kinds of dataacquisition field tests near XIADIAN fault are carried out. In data processing, thedispersion curve is derived with a narrow band-pass filtering cross-correlation methodin SASW, and f-k analysis in MASW, after that the velocity profile and structure areinversed by half-wavelength method and Genetic Algorithm respectively. The contrastbetween the inversed velocity structure and borehole data indicates transient Rayleighwave's reliability in geological survey. The velocity distribution profile shows clearlyvariation of phase velocity near XIADIAN fault. Results mentioned above indicatethat in horizontal inhomogeneous media, SASW and MASW combined processingmethod can reveal effectively the characteristic of shallow velocity structure'shorizontal variation. It has a wide application prospects for detecting inhomogeneousgeological bodies and extension status of shallow fault.In Rayleigh wave's field acquisition research, by processing trial data, the effects oftrace numbers, offset and source are analyzed, and the results indicate that Rayleighwave's frequency band range is related with source energy, receiver's natural frequency and field conditions. If the source energy is strong, the triggered Rayleighwave's main frequency will be low, on the contrary, it will be high. In order todetecting as deeper as possible, high energy source and low natural frequencyreceivers should be used. The stability of test is related with trace numbers, the moretrace numbers the test results more stable, and the dispersion curve more precise, 24channels will be ok in Rayleigh wave exploration. Setting of offset should be definedbased on the depth of target stratum and field's Rayleigh wave phase velocity range.In the paper, MASW is also applied to pick up near-surface velocity structure formreflection profile. The results show that when media's horizontal variation is not solarge, the near-surface velocity structure obtained by Rayleigh wave can offerreference data for static correction in reflection survey.