Kars Investigation by Microgravity and MASW Coupling

A geophysical integrated approach for the detection and characterisation of karst structures in an urban environment was experimented. Microgravity was performed for void detection, together with Multi-channel Analysis of Surface Waves (MASW), aimed to the identification of mechanical weakness areas. <br>Microgravity evidenced negative anomalies corresponding to known conduits and identified the probable extensions of this network in unexplored areas. Control borings, located on these extensions, encountered several levels of water saturated voids, probably belonging to the shallowest part of the karstic system, overlying the main conduits. Simulations, using compact inversion approach for the size and density characterisation of environmental disturbances, confirmed this conclusion. In this context, gravity method proves suitable to the detection of karstic near-surface features. <br>The MASW method, that analyses the Rayleigh wave propagation, can characterise the mechanical behaviour of superficial formations and serve as indicators of subsurface heterogeneities, such as voids or fractures. The MASW evidenced disturbed zones superimposed to gravity anomalies, characterised by the appearance of several dispersion modes, velocity inversions and seismic markers attenuation. One of these features was characterised by low velocities and interpreted as a mechanical weakness area that was confirmed by pressure measurements in the boreholes. <br>