Reply by the authors to discussion by H. Pascal and D. Rankin

The interesting comment by Pascal and Rankin discusses, inter alia, the physical basis of a equation proposed by Schlumberger. This equation expresses formation traveltimes (e.g., inverse phase velocities) derived from measurements made by Schlumberger’s electromagnetic propagation tool (EPT) as the volume weighted sum of the traveltimes of the formation constituents. Pascal and Rankin interpret this equation as implying a layered medium consisting of layers of different dielectric properties. There is no doubt that the Schlumberger traveltime equation is correct for such a layered medium if the direction of wave propagation is normal to the direction of the layering planes. This does not preclude the possibility, however, that the Schlumberger equation may provide an adequate description, at microwave frequencies, of the composite traveltimes of more complex heterogeneous systems.