Simultaneous Analysis of Seismic Velocity and Electrical Conductivity in the Crust and the Uppermost Mantle: A Forward Model and Inversion Test Based on Grid Search

Abstract

This study presents a forward model to quantify the P‐wave velocity (VP), S‐wave velocity (VS), and electrical conductivity (σ) of the solid‐liquid mixtures for a given set of pressure, temperature, lithology, liquid phase (aqueous fluid or melt), liquid fraction, and geometrical parameters in relation to the aspect ratio and connectivity of the liquid phase. This is based on previous experimental and theoretical studies on seismic velocity and electrical conductivity of solid rocks and liquid phases. A total of 78 lithologies, an aqueous fluid with NaCl (∼0–10 wt.%), and mafic to felsic melt appropriate for the crust and the uppermost mantle conditions were described in terms of VP, VS, and σ, as per previous experimental measurements and molecular dynamics simulation. This forward model is provided as a Windows executable program, and generates synthetic VP, VS, and σ, referring to the seismic velocities and electrical conductivity observed in the northeast Japan arc. After generation of the synthetic VP, VS, and σ, the original lithology and liquid parameters (phase, fraction, aspect ratio, and connectivity) were searched by implementing the grid search algorithm to map the misfit over the broad parameter space. The mapping shows the presence of a global misfit minimum around the optimized solution and the possibility of resolving the lithology and the liquid phase parameters based on the observed VP, VS, and σ by using the forward model presented in this study.

Joint Analysis of Seismic and Electrical Observables Beneath the Central Appalachians Requires Partial Melt in the Upper Mantle

“…For the case of the CAA, the electrical conductivity constraints have proven to be particularly important to understanding the character of the geophysical anomaly; while enhanced temperature and partial melt can each potentially explain the seismic observables, the conductivity observations are able to definitively rule out a purely thermal anomaly. This helps to illustrate the importance of co‐located seismic and MT deployments for constraining the structure and properties of the upper mantle, as also demonstrated by other studies (e.g., Chen et al., 2009; Iwamori et al., 2021; McGary et al., 2014; Moorkamp et al., 2007).…”

“…While geophysical observables such as seismic velocity, seismic attenuation, and electrical conductivity are sensitive to these quantities, their interpretation is typically non‐unique, and the uncertainties in translating laboratory experiments to the real Earth are large. A promising strategy for constraining these variables more tightly in regions of interest is to combine co‐located observations of seismic velocity, seismic attenuation, and/or electrical conductivity (e.g., Artemieva et al., 2004; Iwamori et al., 2021; Moorkamp et al., 2007), taking advantage of the fact that these observables have different sensitivities to factors such as temperature, partial melt, water content, and composition (e.g., Cammarano et al., 2003; Dai & Karato, 2014; Faul et al., 2004; Jacobsen et al., 2008; Takei, 2002).…”

Theoretical Issues with Rayleigh Surface Waves and Geoelectrical Method Used for the Inversion of Near Surface Geophysical Structure

“…Therefore, the subsurface lithologies are better delineated. For instance, the occurrence of fluids in the subsurface may be indicated by high electrical conductivity and low seismic velocity [76]. On the other hand, the existence of ore deposits may be revealed by low electrical resistivity and high seismic velocity while the presence of voids may be indicated by high electrical resistivity and low seismic velocity.…”

Large-scale structures in the Earth’s interior: Top-down hemispherical dynamics constrained by geochemical and geophysical approaches

“…Although the spatial resolution is less than some of the seismological observations, electrical conductivity of the Earth's interior is sensitive to the water/hydrogen content and may provide important constraints on the distribution of water in the Earth's interior (e.g., Karato, 2011;Iwamori et al, 2021). For a plausible range in water content in Earth's mantle (10 ppm-1 wt%) at a certain fixed pressure and temperature, the influence of water on electrical conductivity is large, producing a change by a factor of 100-300 for this range of water content.…”