Application analysis of combining high density resistivity and microtremor survey methods in areas of karst collapse：A case study of the collapse in Jili village, Laibin, Guangxi

In order to verify the applicability of geophysical prospecting technology to the investigation of karst collapse, the field research was carried out employing high density resistivity and micro technology methods in Jili village, Laibin City, Guangxi. It showed that the high density symmetric quadrupole sounding method intuitively reflected the thickness of the Quaternary overburden layer and the depth of the low resistivity section underground, while micro technology qualitatively analyzed the surface projection of the underground river and karst fracture zone. This would be more accurate in the case of circling collapse and unfavorable geologic bodies which caused collapse, such as caves, underground rivers, fault fracture zones and soft soil by combing two methods. It also showed that a low resistivity orthogonal point appeared in the high density profiling curve and its value was about 250 Ω?m when the polar distance was 45 m while a great value anomaly appeared on the H/V spectrum and the maximum characteristic frequency was in the range of 2-6 Hz above the underground river or karst fracture zone. On the basis of anomalies in the high density resistivity method and micro method of the line 2, the two sections circled were easy to collapse and one selected to be verified by drilling. Drilling revealed eight caves in limestone covered by a 42 m thick Quaternary overburden, of which the largest cave was up to 5.7 m in height.