arXiv subjects

Ron Maor

Publications and source records attributed to Ron Maor.

4 recordsLinked to original sources

arXiv2025

Learning the nature of viscoelasticity in geologic materials with MCMC

Rock and ice are ubiquitous geologic materials. While apparently solid, they also exhibit fluid behavior under stress - a property termed viscoelasticity. Viscoelastic convection of Earth's mantle drives tectonic plate motion with consequences for earthquakes and sea-level rise, while viscoelastic deformation of ice controls glacier flow and the flexure of icy moons. For crystalline materials, "flow laws" describing bulk rheology can be derived from understanding microstructural dynamics such as crystal-defect migration. Common geologic materials like ice and olivine have grain sizes and crystal orientations that evolve with strain; this complexity precludes a first principles approach. Here we use a Bayesian inference method to learn the connection between microstructure and flow in ice and olivine, from fits to experimental data of these materials undergoing steady-state deformation and forced oscillations. We demonstrate that this method can constrain a nonlinear viscoelastic model for each material, that is capable of capturing both steady and transient dynamics and can also predict dynamics for data it was not trained on. Our results may improve geodynamic models that rely on parameterized constitutive equations, while our approach will be useful for experimental design and hypothesis testing.

physics.geo-ph↗

arXiv2024

A Method for Calculating Attenuation in Creeping Materials

The phase lag between an applied forcing and a response to that forcing is a fundamen tal parameter in geophysical signal processing. For solid deforming materials, the phase lag between an oscillatory applied stress and the resulting strain response encapsulates information about the dynamical behavior of materials and attenuation. The phase lag is not directly measured and must be extracted through multiple steps by carefully comparing two time-series signals. The extracted value of the phase lag is highly sensitive to the analysis method, and often there are no comparable values to increase confidence in the calculated results. In this study, we propose a method for extracting the phase lag between two signals when either one or both include an underlying nonlinear trend, which is very common when measuring attenuation in creeping materials. We demonstrate the robustness of the method by analyzing artificial signals with known phases and quantifying their absolute and relative errors. We apply the method to two experimental datasets and compare our results with those of previous studies

physics.geo-ph↗

arXiv2024

A nanoindentation study of attenuation in geological materials

Viscoelastic behavior in geological materials controls a wide range of geophysical phenomena, such as mantle convection. We present a new method for measuring attenuation in single crystals of minerals and in reference materials over a frequency range of 1-1e-4 Hz via nanoindentation. In the experiments, we calculate the phase lag between a sinusoidal load applied to the tip of the nanoindenter and its displacement into and out of the tested sample, which provides a measure of the inverse quality factor 1/Q (i.e., attenuation) of the sample. Experiments were conducted on polymethyl methacrylate (PMMA), indium, halite, olivine and quartz. Attenuation spectrum from our tests on PMMA and indium are in excellent agreement with reported values from past studies. We quantified the natural damping of the nanoindenter and show that it becomes comparable to that of the samples at frequencies greater than 0.1 Hz, but is much lower at lower frequencies.

physics.geo-ph↗

arXiv2019

On the opposing roles of the Boussinesq and non-Boussinesq baroclinic torques in surface gravity wave propagation

Here we suggest an alternative understanding of the surface gravity wave propagation mechanism based on the baroclinic torque, which operates to translate the interfacial vorticity anomalies at the air-water interface. We demonstrate how the non-Boussinesq term of the baroclinic torque acts against the Boussinesq one to hinder wave propagation. By standard vorticity inversion and mirror imaging, we then show how the existence of the bottom boundary affects the two types of torque. Since the opposing non-Boussinesq torque results solely from the mirror image, it vanishes in the deep water limit and its magnitude is half of the Boussinesq torque in the shallow water limit. This reveals that Boussinesq approximation is valid in the deep water limit, even though the density contrast between air and water is large. The mechanistic roles, played by the Boussinesq and non-Boussinesq parts of the baroclinic torque, remain obscured in the standard derivation where the time-dependent Bernoulli equation is implemented instead of the interfacial vorticity equation. Finally, we note on passing that the Virial theorem for surface gravity waves can be obtained solely from considerations of the dynamics at the air-water interface.

physics.flu-dyn↗