Abstract: A method of determining a physical property of subsurface strata surrounding a borehole. The physical property includes any one or more of stress, strain of fluid pressure of the subsurface strata. The borehole includes a borehole liner having an interior wall. A pair of sensor modules separated by a known distance are clamped to the interior wall of the borehole liner. The clamping induces an acoustic discontinuity in the borehole liner such that a P-wave propagating longitudinally within the borehole liner is at least partially reflected. A respective sensor of each sensor module detecting P-waves propagating in the liner and generating a corresponding sensor output signal indicative of the detected P-waves. A respective sensor output signal from each sensor module is analyzed to detect a resonance in a section of the borehole liner between the sensors. A fundamental frequency of the detected resonance is determined and analyzed to determine the physical property.