Search for: All records

Abstract Receiver functions can be used to estimate the Moho depth (H) and ratio of P to S wavespeed (α/β or κ) in the crust. This is commonly done by grid search, forward modeling travel times to produce so-called “H-κ” stacks of receiver function amplitude. However, radial anisotropy in the crust, which can be significant, is almost never considered in this process. Here, we show that radial anisotropy changes the H-κ stack, biasing interpretations of crustal structure by introducing errors up to ∼3% in H and ∼1% in κ for commonly observed anisotropy magnitudes. We propose a simple method to correct H-κ stacks by incorporating radial anisotropy in the forward calculation. Synthetic tests show that this approach almost completely removes error caused by radial anisotropy. We show examples of this procedure with stations in the eastern United States. We provide readers with code to construct radially anisotropic H-κ stacks. 

Abstract Little has been seismically imaged through the lithosphere and mantle at rifted margins across the continent‐ocean transition. A 2014–2015 community seismic experiment deployed broadband seismic instruments across the shoreline of the eastern North American rifted margin. Previous shear‐wave splitting along the margin shows several perplexing patterns of anisotropy, and by proxy, mantle flow. Neither margin parallel offshore fast azimuths nor null splitting on the continental coast obviously accord with absolute plate motion, paleo‐spreading, or rift‐induced anisotropy. Splitting measurements, however, offer no depth constraints on anisotropy. Additionally, mantle structure has not yet been imaged in detail across the continent‐ocean transition. We used teleseismicS,SKS,SKKS, andPKSsplitting and differential travel times recorded on ocean‐bottom seismometers, regional seismic networks, and EarthScope Transportable Array stations to conduct joint isotropic/anisotropic tomography across the margin. The velocity model reveals a transition from fast, thick, continental keel to low velocity, thinned lithosphere eastward. Imaged short wavelength velocity anomalies can be largely explained by edge‐driven convection or shear‐driven upwelling. We also find that layered anisotropy is prevalent across the margin. The anisotropic fast polarization is parallel to the margin within the asthenosphere. This suggests margin parallel flow beneath the plate. The lower oceanic lithosphere preserves paleo‐spreading‐parallel anisotropy, while the continental lithosphere has complex anisotropy reflecting several Wilson cycles. These results demonstrate the complex and active nature of a margin which is traditionally considered tectonically inactive.