Experimental rock physics: fundamental and applied studies in the laboratory and the field

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Rocks are complex and intriguing materials. In the earth, their physical properties vary with mineral composition, fluid content, tectonic straining, and temperature. Geophysicists probe the earth remotely with seismic and electromagnetic waves; but informed assessments of the field observations require knowledge of the relation between rock properties and in situ conditions. Rock physicists strive to learn more about these relationships and to apply them to field data. The Experimental Geophysics Group led by Dr. Schmitt studies these properties in the laboratory and, uniquely, by field measurements. This research uses tools that range from tiny ultrasonic transducers to large truck mounted seismic energy sources. One problem is that the values of, say, a seismic wave speed given by these varied measurements can be quite different. For example, a seismic wave speed at seismic frequencies will often be substantially less than that obtained using ultrasonic waves. We will address this problem two ways. First, we will constrain this seismic dispersion in the laboratory using 'forced oscillation' methods that will partly employ a new instrument being constructed in our laboratory. Second, we will continue to make fundamental measurements of the behaviour of seismic waves as they travel through a liquid-saturated porous medium in order to test the limits of existing theories. A third component of the research studies the factors controlling the propagation of radar waves that are used to probe near earth structure. This work will be integrated as much as possible with parallel field geophysical studies related to scientific drilling, near-surface hazard characterization, and time-lapse monitoring. Students working in the Experimental Geophysics Group are exposed to a wide range of geoscience problems and all are expected to broaden their exposure by participation in field projects; in the last few years these have ranged over 4 continents and both polar regions.