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Andrew Delorey: Beyond linearity, what can we learn from strain-sensitive velocity measurements
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Andrew Delorey of Los Alamos National Laboratory presents "Beyond linearity, what can we learn from strain-sensitive velocity measurements in the Earth" at the MIT Earth Resources Laboratory on November 18, 2022.
"Many of the most useful and interesting properties of the subsurface, such as stress, permeability, solid-fluid interactions, and material integrity occur or are expressed at compliant internal contacts such as mineral grain boundaries, fractures, and faults. These properties are only weakly expressed in linear elasticity, such as with a simple measurement of seismic travel times. In contrast, nonlinear elastic properties arise almost exclusively from the behavior of internal contacts and fluids within them. Most of what we know about the nonlinear elastic properties of rocks was learned in the laboratory, though there are a few interesting and revealing experiments in the Earth. The lack of experiments in the Earth is primarily due to a lack of techniques that can be widely applied. Here we adapted a pump-probe technique, first developed in the laboratory, to the Earth. In this technique, a rock sample is strained at low-frequency while its elastic properties are repeatedly probed by a high-frequency wave. In this way, we can understand the dependence of the elastic modulus to strain and strain rate. We use solid-earth tides as the low-frequency probe and empirical Green’s functions as the high-frequency probe. Barometric pressure could be substituted as the low-frequency pump. In a study near the San Andreas Fault in California, we were able to observe important aspects of hysteresis and in Oklahoma and New Mexico, we were able to observe stress-induced anisotropy related to the ambient stress field. We are just scratching the surface of what nonlinear elasticity can tell us about subsurface conditions in both reservoir and active tectonic settings."
Andrew Delorey has a M.S. in Geology and Geophysics from the University of Hawaii and a Ph.D. in geophysics from the University of Washington. At UH, he imaged the upper mantle along the Reykjanes Ridge, south of Iceland, to better understand the interaction between the Icelandic mantle plume and the Mid-Atlantic Ridge. At UW, he imaged the Seattle Basin to better understand and predict strong ground motions due to earthquakes on several local faults. Following graduate school, he worked for the U.S. Geological Survey for two years modeling strong ground motions from large subduction zone earthquakes on the Cascadia fault, with particular focus on sedimentary basins. Now at Los Alamos National Laboratory, he has worked on a variety of topics related to energy security, seismic hazard, and nuclear non-proliferation. Regarding energy security and seismic hazard, he has published on earthquake detection and triggered earthquakes as a tool to understand stress conditions, poroelastic conditions, and frictional properties of faults. Most recently, he has worked on adapting laboratory techniques for measuring and interpreting nonlinear elasticity, to in situ Earth studies. He has shown that nonlinear behavior is linked to the stress field and that we can measure aspects of nonlinear hysteresis in the Earth. Supporting nuclear non-proliferation, he has worked on the Source Physics Experiment, whose goals are to discriminate between earthquakes and subsurface explosions, and to learn the source properties of subsurface explosions through modeling and observation. In addition to work at Los Alamos National Laboratory, he spent three years as a visiting scientist at the University of Vienna.
"Many of the most useful and interesting properties of the subsurface, such as stress, permeability, solid-fluid interactions, and material integrity occur or are expressed at compliant internal contacts such as mineral grain boundaries, fractures, and faults. These properties are only weakly expressed in linear elasticity, such as with a simple measurement of seismic travel times. In contrast, nonlinear elastic properties arise almost exclusively from the behavior of internal contacts and fluids within them. Most of what we know about the nonlinear elastic properties of rocks was learned in the laboratory, though there are a few interesting and revealing experiments in the Earth. The lack of experiments in the Earth is primarily due to a lack of techniques that can be widely applied. Here we adapted a pump-probe technique, first developed in the laboratory, to the Earth. In this technique, a rock sample is strained at low-frequency while its elastic properties are repeatedly probed by a high-frequency wave. In this way, we can understand the dependence of the elastic modulus to strain and strain rate. We use solid-earth tides as the low-frequency probe and empirical Green’s functions as the high-frequency probe. Barometric pressure could be substituted as the low-frequency pump. In a study near the San Andreas Fault in California, we were able to observe important aspects of hysteresis and in Oklahoma and New Mexico, we were able to observe stress-induced anisotropy related to the ambient stress field. We are just scratching the surface of what nonlinear elasticity can tell us about subsurface conditions in both reservoir and active tectonic settings."
Andrew Delorey has a M.S. in Geology and Geophysics from the University of Hawaii and a Ph.D. in geophysics from the University of Washington. At UH, he imaged the upper mantle along the Reykjanes Ridge, south of Iceland, to better understand the interaction between the Icelandic mantle plume and the Mid-Atlantic Ridge. At UW, he imaged the Seattle Basin to better understand and predict strong ground motions due to earthquakes on several local faults. Following graduate school, he worked for the U.S. Geological Survey for two years modeling strong ground motions from large subduction zone earthquakes on the Cascadia fault, with particular focus on sedimentary basins. Now at Los Alamos National Laboratory, he has worked on a variety of topics related to energy security, seismic hazard, and nuclear non-proliferation. Regarding energy security and seismic hazard, he has published on earthquake detection and triggered earthquakes as a tool to understand stress conditions, poroelastic conditions, and frictional properties of faults. Most recently, he has worked on adapting laboratory techniques for measuring and interpreting nonlinear elasticity, to in situ Earth studies. He has shown that nonlinear behavior is linked to the stress field and that we can measure aspects of nonlinear hysteresis in the Earth. Supporting nuclear non-proliferation, he has worked on the Source Physics Experiment, whose goals are to discriminate between earthquakes and subsurface explosions, and to learn the source properties of subsurface explosions through modeling and observation. In addition to work at Los Alamos National Laboratory, he spent three years as a visiting scientist at the University of Vienna.
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