Frequency features of microseismic signals

For exploring the frequency features of microseismic signals,the frequency spectrum of the signals was obtained with DB5 in 5 levels,and the instantaneous frequency of the signals was achieved with the windowed Fourier transform.Tendency of frequency attenuation was found.High frequency vibrations did occur early in the microseism,and then the frequency was attenuated because of the damping of rock but not by the frequency dispersion of surface waves.The signals were divided into segments and the frequency spectra were got and the frequency features were achieved and 4 types of variation of frequency were found.Half-period of microseismic signals was gained through computing the intervals of adjacent zeros or adjacent peaks of microseismic signals and the tendency of frequency attenuation was found too.The frequency might correlated to the amplitude.Sometimes the larger(smaller) the amplitude,the lower(higher) the period.The relativity of frequency and amplitude might be caused by the nonlinear creep of the rock and it might be a method of studying nonlinear characteristics of rock.