A thermal disturbance of a rock mass is performed by circulating a fluid through a borehole, a temperature of the circulation fluid differs from a temperature of the rock mass. Before, during and after the thermal disturbance, differential electrical signals proportional to a temperature difference between two points along the borehole are registered by at least one pair of differential temperature transducers disposed along an axis of the borehole Differential electrical signals measured before the thermal disturbance are compared with differential electrical signals measured during the thermal disturbance and differential electrical signals of different temperature transducers positioned along the wellbore borehole are compared with one another. Based on the comparison results of different rock mass areas with different properties are identified.