Structures and dynamics of the subcontinental lithospheric mantle over the Central and Eastern North American continent, constrained by numerical modeling based on tomography models

Abstract

Although earthquakes are typically concentrated along plate boundaries, significant seismicity also occurs within the continental interior, in particular along the Central and Eastern United States (CEUS). In this study, we model the stress induced by mantle convection in CEUS. We consider several global and regional tomography models. Seismic velocity anomalies from the tomography models are converted into density anomalies. Then we compute the instantaneous mantle flow induced by these anomalies, as well as the inferred tectonic regimes and maximum shear stress, SHmax. The derived tectonic regimes are compared to the surface observations obtained from earthquakes focal mechanisms, to assess if the mantle convection may be responsible for the intraplate seismicity in CEUS. The results show that tomography model and viscosity law strongly affect the modeled tectonic regimes, whereas the conversion factor has only a minor influence. The best overall agreement is obtained with the TX2019slab global model (Lu et al., 2019) with Adam et al. (2021) seismic velocity anomalies to density anomalies conversion factor R/vs, and depth-dependent viscosity based on CAM2022 model (Priestley et al., 2024). Most global tomography models recover the compressive regimes observed in the northeastern North American continent, whereas this pattern is generally not reproduced by regional models, suggesting that it may be driven by larger-scale processes. The mantle upwellings beneath BR-RGR (Basin and Range-Rio Grande Rift), region A (Nebraska), region B (Great Lakes, Ontario, Canada), and Bermuda remain across the most tested models, for most of the implemented model parameters, suggesting that these features are real rather than model artifacts. A high-density anomaly between the ETSZ (Eastern Tennessee Seismic Zone) and NMSZ (New Madrid Seismic Zone) is consistently seen in the models and may reflect dense or foundering lithosphere. Overall, these results indicate that large-scale mantle dynamics play an important role in intraplate seismicity in the CEUS. Additional regional shallower processes may be required to explain the remaining misfits, such as the extension observed along the ETSZ, which none of the models or other previous models proposed in the literature have been able to reproduce.