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An RF photonic front-end using dual-differential driving scheme is reported with a 22nm CMOS FD-SOI driver co-integrated with a silicon traveling-wave Mach-Zehnder modulator. A compact design of power splitter and output routing network are implemented on dual-differential driver. An LC input matching network co-designed with bond wire inductance is implemented on a photonic chip to complete the output matching network. The proposed driver is verified with S-parameter and two-tone measurements, achieving 15-25GHz bandwidth with peak 3dBm IIP3 and consumes 448mW. The link performance is demonstrated 12.1% EVM of 16-QAM modulation with 2Gbd at 20GHz carrier frequency. 

The Taconic thrust belt in New England is the type locality of the Ordovician Taconic orogeny, the result of partial subduction of the rifted Laurentian margin beneath the Gondwanan-derived Moretown terrane (MT) and the Shelburne Falls arc. Evidence for Ordovician deformation and metamorphism is only preserved in rocks of the Laurentian margin; Taconic deformation and metamorphism in the MT and suture zone were overprinted by Devonian Acadian tectonism. New thermochronological data from the Taconic thrust belt indicate that many faults were active during the Silurian and Devonian, well after the Taconic orogeny. Crust under accreted terranes in New England is much thinner (~30 km) than below the Grenville belt along the Laurentian margin (~45 km), and Li et al. (2018) noted a particularly abrupt change in crustal thickness in southwestern New England near the suture between Laurentia and the MT. New seismic evidence indicates that the abrupt offset in Moho depth in CT and MA occurs east of an anisotropic region (~25 km wide and ~15 km thick) that lies between the shallow Moho of the MT and the deep Moho of Laurentia. The Taconic and Acadian orogens are narrower in southern New England than they are to the north, suggesting greater crustal shortening, and high-grade metamorphic rocks exposed in southern New England indicate greater erosion of overlying crust. Hillenbrand et al. (2021) proposed that an Acadian plateau existed in southern New England from 380 to 330 Ma and that plateau collapse after 330 Ma led to the abrupt Moho offset. We suggest that an indenter in southern New England focused the Acadian collision between Laurentia and Avalonia leading to greater crustal shortening and uplift than elsewhere the Appalachians. The east-dipping suture zone and Neoproterozoic normal faults cutting the leading edge of Laurentia were reactivated as west-directed thrust faults. Further, the diffuse fault zone that displaced the MT and the leading edge of the Laurentian margin penetrated the crust and displaced the Moho beneath the MT creating a double Moho near the suture. The anisotropic zone between the double Moho region is likely composed of crustal and mantle rocks bounded by faults. It is unclear how far east rifted Grenville crust extends under the MT; it is possible that the MT is no longer above its original lithospheric mantle. 

Ganderia and the Southeastern New England Avalon terrane are both terranes that rifted from Gondwana and accreted to North America in the early to mid-Paleozoic. Accretion of the Avalon terrane was accompanied by plutonism, deformation, and metamorphism including partial melting within the Nashoba terrane, the trailing edge of Ganderia, and may be interpreted as indicators for mid- to lower-crustal channel flow. Channel flow describes the flow of weak, partially molten material between more competent crust as a result of pressure gradients in the mid- to lower crustal levels. Such flow should typically result in seismic anisotropy due to the crystallographic preferred orientations of minerals and shape preferred orientations at various scales. Here, we present first results for the crustal anisotropic structure beneath the Nashoba terrane that were produced with a newly developed approach from currently collected data in the region. To investigate the hypothesis of crustal flow during the orogenic history of Southeastern New England, we deployed a dense profile of 6 broadband seismic stations crossing the Nashoba terrane. We analyze the harmonic variation of amplitudes in teleseismic P-Receiver Functions (RFs) to identify interfaces of isotropic and anisotropic contrasts within the crust. In the case of particularly prominent anisotropic features that have significantly larger amplitudes than other signals, it is feasible to derive quantitative constraints on the strength and orientation of the anisotropy. However, with growing complexity, a classical forward modelling or grid search approach becomes unfeasible. These difficulties can be mitigated by applying Bayesian inversion, which infers values of model parameters from a probabilistic perspective. Applying a Bayesian inversion to the harmonically decomposed RFs has the potential to infer complex anisotropic seismic structures. We find evidence for two crustal anisotropic layers with confined properties to the geologic units of the Ganderia, Nashoba and Avalon terranes that might be related to episodes of lower crustal flow. In addition, we identify anisotropy at shallow mantle levels beneath the Nashoba and Avalon Terranes possibly indicating the upper interface of a shallow asthenosphere in the region. 

Seismic waves with different propagation and oscillation directions can exhibit different velocities when going through a medium with some directional properties; this phenomenon is called seismic anisotropy. Seismic anisotropy observed beneath eastern North America is often attributed to present-day flow in the upper mantle. The mantle flow causes shear waves oscillating in the direction of flow (e.g., in the direction of North America plate motion) to travel faster than those that travel in other directions. However, this pattern does not hold true for some regions along the Appalachian orogen, suggesting that past tectonic events can result in long-lived, ‘frozen-in’ anisotropy in the lithosphere, which modifies the predicted anisotropic behavior beneath these regions. In this study, we investigate sources of seismic anisotropy beneath southern New England using a method based on directionally dependent variations of P-wave to S-wave conversions at interfaces with contrasts in anisotropy. This method can separate signals caused by different anisotropic features and constrain the depth distribution of anisotropy. Within the crust there are multiple features that may be correlated with stratification in the Hartford Basin, faults in the Taconic thrust belt, shear zones formed during Salinic/Acadian terrane accretion events, and orogen-parallel crustal flow in the Acadian orogenic plateau. We apply a Bayesian inversion method to obtain quantitative constraints on the direction and strength of intra-crustal anisotropy beneath the Hartford Basin. In the upper mantle, we identify a fossil shear zone possibly formed during oblique subduction of Rheic Ocean lithosphere. We also find evidence for a plate motion-parallel flow zone in the asthenosphere that is likely disturbed by mantle upwelling near the southern margin of the Northern Appalachian Anomaly in the eastern part of the study area. 

Ganderia and the Southeastern New England Avalon terrane, are both terranes that rifted from Gondwana and accreted to North America in the early to mid-Paleozoic. Accretion of the Avalon terrane was accompanied by plutonism, deformation, and metamorphism including partial melting within the Nashoba terrane, the trailing edge of Ganderia and may be interpreted as indicators for mid- to lower-crustal channel flow. Channel flow describes the flow of weak, partially molten material between more competent crust as a result of pressure gradients in the mid- to lower crustal levels. Such flow should typically result in seismic anisotropy due to the crystallographic preferred orientations of minerals and shape preferred orientations at various scales. Here, we present a new method designed to analyze the crustal anisotropic structure beneath the Nashoba terrane and provide insight into its capabilities in a first application to permanent stations in the area and currently collected data. To investigate the hypothesis of crustal flow during the orogenic history of Southeastern New England, we deployed a dense profile of 6 broadband seismic stations crossing the Nashoba terrane. We analyze the harmonic variation of amplitudes in teleseismic P-Receiver Functions (RFs) to identify interfaces of isotropic and anisotropic contrasts within the crust. In the case of particularly prominent anisotropic features that have significantly larger amplitudes than other signals, it is feasible to derive quantitative constraints on the strength and orientation of the anisotropy. However, with growing complexity, a classical forward modelling or grid search approach becomes unfeasible. These difficulties can be mitigated by applying Bayesian inversion, which infers values of model parameters from a probabilistic perspective. Here we use a Bayesian framework to invert for the anisotropic model that best fits the observed constant and harmonic terms. Applying a Bayesian inversion to the harmonically decomposed RFs instead of full RF waveforms has the potential to infer the anisotropic seismic model more faithfully, without attempting to fit unrelated signals and artifacts. 

The New England Appalachians provide a fascinating window into a host of fundamental geological problems. These include the modification of crustal and mantle lithospheric structure via orogenesis, terrane accretion, and continental rifting, the evolution of individual terranes through processes such as channel flow and ductile extrusion, and the causes and consequences of the Northern Appalachian Anomaly (NAA), a prominent geophysical anomaly in the upper mantle. Recent and ongoing deployments of dense seismic arrays in New England are providing images of the crust and upper mantle in unprecedented detail, allowing us to address both new and longstanding science questions. These deployments include the Seismic Experiment for Imaging Structure beneath Connecticut (SEISConn, 2015-2019), the New England Seismic Transects (NEST, 2018-present), and the GEology of New England via Seismic Imaging Studies (GENESIS, 2022-present) arrays. Here we present results from these experiments that are shedding new light on the tectonic evolution of New England and the ways in which structures and processes in the upper mantle can affect the structure of the overlying lithosphere. These include detailed new images of crustal architecture beneath central and southern New England, including a sharp transition from thick (~48 km) crust Laurentia terranes to thin (~32 km) crust beneath Appalachian terranes. The character of this offset beneath the SEISConn and NEST arrays suggests an overlap of two Moho boundaries, forming an overthrust-type structure that may have resulted from reactivation of faults during the compression and shortening associated with the formation of the hypothesized Acadian Altiplano. Beneath SEISConn, there is evidence for multiple relict structures preserved in the lithosphere from past episodes of terrane accretion and suturing, as well as anisotropic layering that constrains the kinematics of past lithospheric deformation events. Beneath the NEST line in central New England, we infer a relatively shallow (~80 km) lithosphere-asthenosphere boundary above the NAA upper mantle geophysical anomaly, providing evidence for lithospheric thinning above a presumed asthenospheric upwelling. Finally, preliminary results suggest layered crustal anisotropy beneath the GENESIS array, perhaps corresponding to a past episode of channel flow in the mid-crust.