Laser-based seismic imaging of analogue models

We present and demonstrate our new application of a geophysical seismic technique to acoustically characterise and image layers with different impedance contrast in analogue models. A high-powered pulsed laser in combination with a mirror galvanometer is used to generate a powerful acoustic shockwave at any point of the surface of the analogue model. Reflections, refractions, and diffractions of the acoustic source wave, induced by internal structures inside an analogue model, produce vibrations of the top surface of a model, which are measured by laser vibrometer.

Using our setup, we acquire seismic receiver gathers in less than a minute. Interpretation of the gathers allowed to identify the presence of internal reflecting and refracting material interfaces. In a series of test models, we determined the speed of both P-waves and surface waves in a multitude of brittle analogue materials. In uniform layered models we performed 1D inversion using the gathered waveform data. The results are validated by simulating the test experiments in a finite-difference solver. The novel method will be developed further, aiming to determine stress build-up in the material prior to fault formation or activity.