Stimulated infrared emission from rocks: assessing a stress indicator
10 Jan 2007
1Ecosystems Science and Technology Branch, Code SGE, NASA Ames Research Center, Moffett Field, CA 94035-1000, USA
2Department of Physics, San Jose State University, San Jose, CA 95192-0106, USA
3Department of Chemistry, Niigata University, Ikarashi-ninotyo, Niigata 950-2181, Japan
4Department of Civil Engineering, San Jose State University, San Jose, CA 95192-0083, USA
5Department of Civil Engineering, University of Maryland, College Park, MD 20742, USA
6Jet Propulsion Laboratory, Org. 3880, Pasadena, CA 91109-8099, USA
7CEORS, George Mason University, Fairfax, VA 22030-4444, USA
Abstract. To study the effect of stress-activated positive hole (p-hole) charge carriers on the infrared (IR) emission from rocks, we subjected a portion (~10 vol.%) of a large (30×60×7.5 cm3) block of anorthosite, a nearly monomineralic (Ca-rich feldspar) igneous rock, to uniaxial deviatory stress up to failure. We measured the IR emission from a flat surface ≈40 cm from the stressed rock volume over the 800–1300 cm−1 (7.7–12.5 μm) range. Instantly, upon loading, the emission spectrum and intensity change. At first narrow bands appear at 930 cm−1 (10.75 μm), 880 cm−1 (11.36 μm), 820 cm−1 (12.4 μm) plus additional narrow bands in the 1000–1300 cm−1 (7.7–10.0 μm) range. The 10.75–12.4 μm bands are thought to arise from vibrationally excited O-O stretching modes, which form when p-hole charge carriers, which spread from the stressed rock volume into the unstressed rock, recombine at the surface. They radiatively decay, giving rise to "hot" bands due to transitions between excited states. Before failure the broad emission bands at 1170 cm−1 and 1030 cm−1 (8.7 and 9.7 μm) also increase slightly in intensity, suggesting a small increase in temperature due to thermalization of the energy deposited into the surface through p-hole recombination. Stimulated IR emission due to hole-hole recombination and its follow-on effects may help understand the enhanced IR emission seen in night-time satellite images of the land surface before major earthquakes known as "thermal anomalies".
Citation: Freund, F. T., Takeuchi, A., Lau, B. W. S., Al-Manaseer, A., Fu, C. C., Bryant, N. A., and Ouzounov, D.: Stimulated infrared emission from rocks: assessing a stress indicator, eEarth, 2, 7-16, doi:10.5194/ee-2-7-2007, 2007.