Karst detection by geophysical methods using microseismic sounding

Abstract

Research aim is to test a technique for detecting buried karst using microseismic sounding based on spectral amplification of horizontal displacements. The main research tasks include the construction and analysis of geoelectric and microseismic sections. Methodology. The microseismic background was recorded using the OMAR-2s autonomous seismic station (Institute of Geophysics Ural Branch RAS, Ekaterinburg) in the frequency band 1–1000 Hz. Low-frequency horizontal seismic receivers from OYO Geospace Corporation were used as sensors. Vertical electrical sounding (VES) was carried out by a set of ERA-MAX equipment (SPC “ERA”, St. Petersburg) using a symmetrical Schlumberger installation at a frequency of 4.88 Hz, at currents of 5–50 mA. VES processing consisted in quantitative one-dimensional inversion according to the IPI2Win program (Moscow State University, Moscow). Results. Experimental and methodological work on the study of microseisms, accompanied by VES, was carried out on two karst sites of the Sverdlovsk region. Based on the results of processing, geoelectric and microseismic sections were constructed to determine the conditions of occurrence of bedrock and loose sediments covering them, as well as to identify local anomalies associated with karst manifestations. The results of electrical exploration and seismometry are in good agreement with each other and are confirmed by geological data. Conclusions. Vertical electrical sounding makes it possible to distinguish karst by the high contrast of the resistances of the host bedrock (limestone) and terrigenous filler material (clay, loam). Microseismic sounding makes it possible to delineate karst zones by high values of spectral amplification of weakly consolidated karst deposits, relatively low levels of microseisms in bedrock. Thus, on the basis of complex electrical and microseismic soundings, it is possible to confidently identify the areas of development of karst processes.