Crustal and Upper Mantle Structure Beneath the Southeastern United States From Joint Inversion of Receiver Functions and Rayleigh Wave Dispersion

Abstract

Using data from 186 stations belonging to the USArray Transportable Array, a three‐dimensional shear wave velocity model for the southeastern United States is constructed for the top 180 km by a joint inversion of receiver functions and Rayleigh wave phase velocity dispersion computed from ambient noise and teleseismic earthquake data. The resulting shear wave velocity model and the crustal thickness and Vp/Vs (κ) measurements show a clear spatial correspondence with major surficial geological features. The distinct low velocities observed in the depth range of 0–25 km beneath the eastern Gulf Coastal Plain reflect the thick layer of unconsolidated or poorly consolidated sediments atop the crystalline crust. The low κ (1.70–1.74) and slow lowermost crustal velocities observed beneath the eastern Southern Appalachian Mountains (including the Carolina Terrane and Inner Piedmont) relative to the adjacent Blue Ridge Mountains and Valley and Ridge can be interpreted by lower crustal delamination followed by relamination. The Osceola intrusive complex in the central Suwannee Terrane has similar crustal characteristics as the eastern Southern Appalachian Mountains and thus can similarly be attributed to crustal delamination/relamination processes. The Grenville Province and adjacent areas possess relatively high κ values which can be attributed to mafic intrusion associated with crustal extension in a recently recognized segments of the eastern arm of the Proterozoic Midcontinent Rift.

Lithospheric Evolution of the South‐Central United States Constrained by Joint Inversion of Receiver Functions and Surface Wave Dispersion

“…This leads to densification and delamination of the crust's bottom (Bousquet et al., 1997; Rey, 1993). Such crustal thinning by delamination has been suggested in other regions along the southeastern passive continental margin, including the Carolina Terrane and Inner Piedmont of the southern Appalachian Mountains (Parker et al., 2013; Q. Yang et al., 2021).…”

“…The procedures and parameters for the determination of the prior and posterior distributions closely followed the method of Shen et al. (2013), with applications for regional investigations in the continents of North America and Africa (Shen & Ritzwoller, 2016; T. Wang et al., 2022; Q. Yang et al., 2021).…”

Crustal Structure and Anisotropy Measured by CHINArray and Implications for Complicated Deformation Mechanisms Beneath the Eastern Tibetan Margin

“…Therefore, the observed crustal anisotropy also disfavors the presence of an organized lower crust flow in the eLVZ area. In fact, all the most recent tomographic studies (e.g., Y. Yang et al., 2020; X. Yang et al., 2023; Zhang et al., 2020) showed that the eLVZ is disconnected from the wLVZ, suggesting that it has a different origin from the wLVZ, such as mantle upwelling (Z. Huang et al., 2015) or crustal thickening and partial melting in the mid‐lower crust (Zhang et al., 2020).…”

“…As river incision data supported the lower crust flow model for the crustal uplift in this area (Clark et al., 2005), many magnetotelluric and seismic investigations have been conducted to image the lower crustal flow. While magnetotelluric images suggested that high electrical conductivity structures in the lower crust are localized in two continuous channels that run roughly from north to south (Bai et al., 2010), seismic images, on the other hand, showed two distinct LVZs beneath the SYRB and the SCB (e.g., Bao et al., 2015; M. Chen et al., 2014; Y. Liu et al., 2023; Shen et al., 2016; Y. Yang et al., 2020; X. Yang et al., 2023; Zhang et al., 2020). The two LVZs seem to be separated by the inner zone of the ELIP and will be referred to as eLVZ and wLVZ, respectively (Figure 7b).…”

“…Due to the low station density in the area as well as the limited ability of traveltime tomography in imaging low‐velocity structures, the lateral resolution of early traveltime tomography is relatively low. Recent deployment of the CHINArray and incorporation of ambient noise data, together with the improvement in seismic tomography have led to high resolution images of the crust beneath the eastern margin (e.g., Bao et al., 2015; Y. Liu et al., 2023; Shen et al., 2016; Y. Yang et al., 2020; X. Yang et al., 2023; Zhang et al., 2020). All the tomographic models showed a large scale low‐velocity anomaly beneath the SGB, which extends southward to the northern part of the SYRB.…”