Fractal analysis of geoacustic signals registered at bishkek geodynamic polygon
During the special experiments conducted in 2008-2012 at the territory of the Bishkek geodynamic polygon, geoacoustic responses of rocks under natural conditions to electrical impulses of electrical prospecting generator ERGU-600-2 were recorded. The results showed that when geophones were placed in wells, the responses of geoacoustic emissions were recorded at low intensities of electric field ~0.5 mV/m and appeared as short pulse high-amplitude signals exceeding the root mean square noise more than 3 times. This paper presents the results of analysis of geoacoustic signals at stationary measuring site, under conditions where responses are not distinguished from the noise level. This feature dictates using of fractal methods that make it possible to extract additional information from signals in which the amplitude of useful component is commensurable with the noise level. We used Detrended Fluctuation Analysis (DFA) as the method for estimation of fractal characteristics (Hurst exponent). Calculation of Hurst exponent in a sliding window showed that a sharp decrease in Hurst exponent values coincides in time with the running of ERGU-600-2. In the background periods (in the absence of electromagnetic impact), values of Hurst exponent fluctuate at a level of ~ 0.5, indicating the absence of correlation in the signal during this period (classical Brownian motion). The detected responses of geoacoustic emission to the sensing pulses confirm the possibility of current pulses impact on the process of geomedia destruction, which is consistent with the results obtained by other researchers in this field.