Imaging fractures in a massive limestone with ground penetrating radar, Haymana, Turkey

This study was conducted by utilizing ground-penetrating radar (GPR) to determine the subsurface conditions of the Mollaresul High Plateau located in Haymana, Ankara, Turkey. The site is thought to be managed as a marble quarry. The GPR reflection profiling method was used because it could be applied rapidly and non-invasively without causing any damage to the surveyed area. Approximately N-S directed measurements were collected on 10 profiles using the Ramac CU II GPR system and 100 MHz unshielded antennae. During the data processing stage, the instantaneous amplitude and combined analysis of the phase-group sections were added to the basic processing steps in order to obtain more detailed images of the shallow subsurface in phase-group sections and the energy distribution of the traces in the instantaneous amplitude sections. The conditions of the environment were in the vadose zone and the electrical conductivity of the marble was low. Georadar yielded penetration depths of about 40 and 45 m below ground level. The joint interpretation of the instantaneous amplitude and phase-group sections highlighted strong reflectors, which are indicative of the locations, extensions and sizes of the main fractures in the rock mass. The continuous sub-horizontal reflections found at a maximum depth of 45 m within the marble mass were monitored on the interpreted radargrams to image the extension of fractures. The locations of more massive blocks surrounded by weathered material, low-angle joints and fractured rocks with specific inclinations were also determined. The results highlighted whether the quarries are exploitable or not. With such useful information, unnecessary excavations are avoided and the quarrier gains substantially in terms of time and cost.   Key words: Georadar, instantaneous amplitude and phase group attributes, marble, fracture-crack images, Turkey.