47 research outputs found
Plate-scale imaging of eastern US reveals ancient and ongoing continental deformation
No full text<p>This is the tomography dataset from "Plate-scale imaging of eastern US reveals ancient and ongoing continental deformation", submitted to <em>Geophysical Research Letters</em> in 2024-02. A Matlab file is included, which can also be opened using Python with Scipy loadmat function. The file contains a structure with the following fields: </p>
<p>lon, lat, z, vs: Velocity and positions, each with shape nlon x nlat x nz. </p>
<p>z_moho, z_sediment, z_lab_1150: depths to each of these layers. The LAB is to the 1150 C isotherm. Shapes are nlon x nlat. </p>
<p>We also include surface wave datasets produced from ambient noise tomography (Lynner and Porrit, 2019), and earthquake Helmholtz tomography (Lynner et al., 2019). See files ENAM_RAYLEIGH_ANT_LYN2017.zip and ENAM_RAYLEIGH_LYNNER_EQ_HELM.zip. </p>
<p>Lynner, C., Guajardo, A., Eilon, Z., & Janiszewski, H. A. (2019). Surface wave tomography across the Eastern North American Margin from amphibious data<em> </em>[Dataset]. <em>2019</em>, T21F-0376.</p>
<p>Lynner, C., & Porritt, R. W. (2017). Crustal structure across the eastern North American margin from ambient noise tomography [Dataset]. <em>Geophysical Research Letters</em>, <em>44</em>(13), 6651–6657. https://doi.org/10.1002/2017GL073500</p>
Crustal structure across the eastern North American margin from ambient noise tomography
No full textPassive tectonic margins, like the eastern North American margin (ENAM), represent the meeting of oceanic and continental material where no active deformation is occurring. The recent ENAM Community Seismic Experiment provides an opportunity to examine the crustal structure across the ENAM owing to the simultaneous deployment of offshore and onshore seismic instrumentation. Using Rayleigh wave phase and group velocities derived from ambient noise data, we invert for shear velocity across the ENAM. We observe a region of transitional crustal thicknesses that connects the oceanic and continental crusts. Associated with the transitional crust is a localized positive gravitational anomaly. Farther east, the East Coast magnetic anomaly (ECMA) is located at the intersection of the transitional and oceanic crusts. We propose that underplating of dense magmatic material along the bottom of the transitional crust is responsible for the gravitational anomaly and that the ECMA demarks the location of initial oceanic crustal formation.6 month embargo; published online: 3 July 2017This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
Sub‐slab anisotropy beneath the Sumatra and circum‐Pacific subduction zones from source‐side shear wave splitting observations
No full textTesting models of sub‐slab anisotropy using a global compilation of source‐side shear wave splitting data
No full text
Mantle dynamics of the Andean Subduction Zone from continent-scale teleseismic S-wave tomography
No full textThe Andean Subduction Zone is one of the longest continuous subduction zones on Earth. The relative simplicity of the two-plate system has makes it an ideal natural laboratory to study the dynamics in subduction zones. We measure teleseismic S and SKS traveltime residuals at >1000 seismic stations that have been deployed across South America over the last 30 yr to produce a finite-frequency teleseismic S-wave tomography model of the mantle beneath the Andean Subduction Zone related to the Nazca Plate, spanning from ~5°N to 45°S and from depths of ~130 to 1200 km. Within our model, the subducted Nazca slab is imaged as a fast velocity seismic anomaly. The geometry and amplitude of the Nazca slab anomaly varies along the margin while the slab anomaly continues into the lower mantle along the entirety of the subduction margin. Beneath northern Brazil, the Nazca slab appears to stagnate at ~1000 km depth and extend eastward subhorizontally for >2000 km. South of 25°S the slab anomaly in the lower mantle extends offshore of eastern Argentina, hence we do not image if a similar stagnation occurs. We image several distinct features surrounding the slab including two vertically oriented slow seismic velocity anomalies: one beneath the Peruvian flat slab and the other beneath the Paraná Basin of Brazil. The presence of the latter anomaly directly adjacent to the stagnant Nazca slab suggests that the plume, known as the Paraná Plume, may be a focused upwelling formed in response to slab stagnation in the lower mantle. Additionally, we image a high amplitude fast seismic velocity anomaly beneath the Chile trench at the latitude of the Sierras Pampeanas which extends from ~400 to ~1000 km depth. This anomaly may be the remnants of an older, detached slab, however its relationship with the Nazca-South America subduction zone remains enigmatic.Fil: Rodríguez, Emily E.. University of Arizona; Estados UnidosFil: Portner, Daniel Evan. No especifíca;Fil: Beck, Susan L.. University of Arizona; Estados UnidosFil: Rocha, Marcelo P.. Universidade do Brasília; BrasilFil: Bianchi, Marcelo B.. Universidade de Sao Paulo; BrasilFil: Assumpção, Marcelo. Universidade de Sao Paulo; BrasilFil: Ruiz, Mario. Escuela Politécnica Nacional; EcuadorFil: Alvarado, Patricia Monica. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Geofísica y Astronomía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; ArgentinaFil: Condori, Cristobal. Universidade do Brasília; BrasilFil: Lynner, Colton. University Of Delaware; Estados Unido
Plate‐Scale Imaging of Eastern US Reveals Ancient and Ongoing Continental Deformation
No full textAbstract:
Eastern North America was constructed over several Wilson cycles, culminating in the breakup of Pangea. Previous seismological imaging lacked the resolution to depict precisely how ancient tectonic boundaries manifest throughout the lithosphere, how continental breakup modified the plate, or how ongoing mantle dynamics shapes the continental margin. We present a high‐resolution, plate‐scale seismic tomography model of the eastern US by combining an unprecedented suite of complementary data sets in a Bayesian framework. These data provide detailed resolution from crust to asthenosphere, identifying the base of the lithosphere and mid‐lithospheric discontinuities. The plate thins in steps that align with ancient orogens. The lithospheric step at the Appalachian front is associated with cells of mantle upwellings, likely edge‐driven convection, that erode the base of the plate and shape modern Appalachian topography. Low‐velocity structures in the lithospheric‐mantle align with the Grenville front and may be remnants of Rodinia assembly
‐Wave Tomography
No full textAbstract 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 teleseismic S, SKS, SKKS, and PKS splitting 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
