EAR-PF: Investigating the lithospheric structure and the origins of seismic anomalies in the Southwestern United States using a joint seismic analysis

Golos, Eva, Cambridge MA

Investigators

Abstract

An EAR Postdoctoral fellowship has been awarded to Dr. Eva Golos to carry out research and education plans at Brown University under the mentorship of Professor Karen Fischer. She aims to understand the structure and evolution of the lithosphere under the southwestern United States by integrating information from different types of seismic waves. The research will focus on how various factors such as temperature, rock composition, and melting control the structure and strength of the present-day lithosphere, and how this interplay has guided tectonic evolution over geologic time scales. Dr. Golos will develop a new inversion method using a variety of seismic data, including surface waves, seismic waves that traverse the lithosphere, and those that have been reflected or converted from one type of seismic wave to another. The combination of input data will produce models with more resolution. Interpretation of the resulting seismic model will be carried out alongside forward-modeling of the effects of melt and anisotropy (the dependence of the speed of seismic wave propagation on vibration direction). Information from a number of scales must be synthesized from the grain-scale to sharp discontinuities in the mantle to the entire depth extent of the lithosphere. The findings will yield insight into how lithospheric properties affect deformation and surface dynamics, with implications for natural hazards such as earthquakes and volcanoes. These applications provide a natural starting point for outreach activities, which will be done through programs aimed at elementary school audiences as well as through teaching and undergraduate mentoring. Many unanswered questions pertain to the nature of the continental lithosphere, and particularly the relative roles of temperature, compositional variations, anisotropic structures, and the presence and abundance of partial melt. This work aims to understand these factors and their effects on lithospheric structure, thickness, and strength; on deformation and the response at the surface to tectonic forces; and on the evolution and fate of the continental lithosphere. The southwestern United States will be used as a case study, to probe the origins of geophysical anomalies associated with the Colorado Plateau, Basin and Range Province, and Rio Grande Rift. The approach taken will be two-pronged. First, a seismic model will be developed incorporating a variety of networks including the USArray Transportable Array, Earthscope FlexArray deployments, and permanent broadband stations. A model of shear wavespeed and discontinuity structure will be generated through a Bayesian inversion of a plethora of seismic data, including P-to-s and S-to-p receiver functions, Rayleigh wave phase velocity dispersion, and body wave reflectivity autocorrelograms. The complementary nature of these data will help resolve smooth large-scale features as well as sharp boundaries and discontinuities. Variations in receiver functions at different frequency bands, and from different directions, can be used to infer the sharpness and the anisotropic properties of interfaces, respectively. The second part of this investigation involves using forward modeling to estimate the relative effects of thermal, compositional, and melt-related properties on seismic structure, and to provide constraints on their interplay at regional-to-continental scales. This project was funded jointly by the Geophysics program in the Division of Earth Sciences and the Established Program to Stimulate Competitive Research (EPSCoR) office. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.