Development of 3-D shear wave models using a multi-objective optimization scheme

Lennox Thompson, University of Texas at El Paso

Abstract

Evidence of geologic activity still occurring in Rio Grande Rift (RGR) includes quaternary faulting, seismicity, and widening at a small rate. We map the crustal thickness and seismic velocity ratio to create crustal model cross sections that highlights the regional extension of the Southern Rio Grande Rift (SRGR). Specifically, we compute receiver functions and receiver function stacks for 147 USArray and previously collected data, and interpolate the crustal and velocity results using a kriging interpolation scheme. By incorporating gravity, magnetics, receiver functions, velocity models, and the interpretation of seismic reflection/refraction data, we produce a constrained crustal model that characterizes the evolution of the SRGR. In consequence, important questions related to tectonic and lithospheric activity of the Rio Grande Rift remain unresolved. To address some of these geological questions, we developed a 3-D crust and upper mantle velocity model using a constrained optimization approach for joint inversion of surface wave and receiver functions. Our 3-D models show a thin lower velocity crust anomaly along the southern east portion of the Rio Grande Rift, a persistent low velocity anomaly underneath the Colorado Plateau and Basin and Range province, and another one at depth beneath the Jemez lineament, at the southern RGR. ^ Furthermore, to make the joint inversion process more robust, we use multi-objective optimization technique: namely, we repeatedly solve the joint inversion problem with different possible combinations of variances. From the mathematical viewpoint, such solutions form a Pareto front of the corresponding multi-objective optimization problem. If a certain geological feature is visible in all these solutions, then we can be confident that this feature is also present in the actual solution corresponding to the actual (unknown) values of the variances – i.e., that it is the feature of the actual Earth structure. We applied this more robust optimization technique to the Texas region and we also compared the structure of the upper mantle with other ancient and/or active rift systems within the Texas region. Our resulting 3-D velocity models will helps us to better understand the tectonic history and physical properties of the Earth structure and also determine if an ancient rift system within Texas is reactivated or not.^

Subject Area

Geophysics

Recommended Citation

Thompson, Lennox, "Development of 3-D shear wave models using a multi-objective optimization scheme" (2015). ETD Collection for University of Texas, El Paso. AAI3708572.
http://digitalcommons.utep.edu/dissertations/AAI3708572

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