Seismic Anisotropy Tomography and Mantle Dynamics of Central‐Eastern USA

Abstract

We present high‐resolution 3‐D tomographic models of isotropic P‐wave velocity (Vp), azimuthal anisotropy, and radial anisotropy down to 1,300 km depth beneath the central and eastern United States (CEUS), which are obtained by inverting a great number of local and teleseismic data and making a whole‐mantle correction to teleseismic travel‐time data recorded by the USArray. Trade‐offs between azimuthal and radial anisotropies occur due to the correlation between the azimuthal and incidence angles of seismic rays, but the use of uniform and crisscrossing rays can reduce the trade‐off effect. Our tomographic images reveal the North American Craton with layered anisotropy and strong anisotropies in the lower mantle related to the deeply subducted Farallon slab and passage of the Bermuda hotspot. In the upper mantle, low‐velocity anomalies with significant seismic anisotropy are revealed beneath three intraplate seismic zones in New Madrid, East Tennessee, and South Carolina, suggesting that hot and wet mantle upwelling occurs under the seismic zones, and the related fluids affect the earthquake generation. The most important dynamic processes in the mantle beneath the CEUS are the deep subduction of the Farallon plate and the passage of the Bermuda hotspot, which have caused strong structural heterogeneities, seismic anisotropy, as well as thermal anomalies and fluids that contributed to the formation of intraplate seismic zones in the CEUS.

Mantle Tomography of Central‐Eastern USA: Influence of Inversion Volume Size

“…Moreover, Thomas and Powell (2017) proposed that most intraplate seismic zones are developed from ancient rifts or tectonic sutures, which happened for all the three seismic zones (i.e., NMSZ, ETSZ, and SCSZ) in the CEUS. Hence, hydrous mantle upwelling induced by the Bermuda hotspot passage and/or the subducted Farallon slab may have contributed to the lithospheric weakness and ancient fault reactivation, which further facilitated the formation of the intraplate seismic zones.Our tomographic images reveal similar crustal structures and seismogenic processes of the three intraplate seismic zones, but their mantle structures and processes may be different, which should be investigated by using seismic anisotropy tomography (e.g., Liang et al., 2022).…”

Gondwanan flood basalts linked seismically to plume-induced lithosphere instability

“…Like the proposed high-wavespeed lithospheric fragment related to the CRB Flood Basalt event, the mid-North American high-wavespeed anomaly lies above the inferred location of the subducted Farallon slab ( Fig. 1 C ) ( 16 – 20 ). The concurrence of the reconstructed positions of high-wavespeed delaminated lithosphere in the mantle and thinned lithosphere at the surface indicates that the delaminated materials sink quasi-vertically, even beneath the fast-moving North America plate (~2 cm/y).…”

Tilting‐Axis Anisotropic Tomography and Subduction Dynamics of the Java‐Banda Arc

“…The two FVDs have been confirmed by previous studies of azimuthal and radial anisotropies (e.g., Cao et al., 2021; Koulakov et al., 2009; Liang et al., 2022). The trench‐normal and nearly upright FVPs have been observed in the mantle wedge beneath Japan (Wang & Zhao, 2021) and Alaska (Liang et al., 2024). The similar features widely distributed in the deep upper mantle (Region C) revealed by this study are well consistent with the expected anisotropic characteristics of the BMW convection flow.…”

“…The obtained 3‐D numerical simulation results (e.g., Confal et al., 2018; Faccenda & Capitanio, 2013) and seismic tomographic models (e.g., VanderBeek & Faccenda, 2021; Wang & Zhao, 2021) are more consistent with various geophysical observations. The tilting‐axis anisotropic tomography has been applied to investigate the detailed 3‐D anisotropic structures beneath Japan (Wang, Zhao, & Chen, 2022; Wang & Zhao, 2021), Cascadia (Liang et al., 2023), Central Mediterranean (Rappisi et al., 2022), and Alaska (Liang et al., 2024), providing new insights into subduction dynamics. Xie et al.…”