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  1. Recent investigations in polar environments have examined solid-Earth-ice-sheet feedbacks and have emphasized that glacial isostatic adjustment, tectonic, and geothermal forcings exert first-order control on the physical conditions at and below the ice-bed interface and must be taken into account when evaluating ice-sheet evolution. However, the solid-Earth structure beneath much of Antarctica is still poorly constrained given the sparse distribution of seismic stations across the continent and the generally low seismicity rate. One region of particular interest is the Wilkes Subglacial Basin (WSB) in East Antarctica. During the mid-Pliocene warm period, the WSB may have contributed 3-4 m to the estimated 20 m rise in sea-level, indicating that this region could also play an important role in future warming scenarios. However, the WSB may have experienced notable bedrock uplift since the Pliocene; therefore, past geologic inferences of instability may not serve as a simple analogue for the future. Using records of ambient seismic noise recorded by both temporary and long-term seismic networks, along with a full-waveform tomographic inversion technique, we are developing improved images of the lithospheric structure beneath East Antarctica, including the WSB. Empirical Green’s Functions with periods between 40 and 340 s have been extracted using a frequency-time normalization technique, and a finite-difference approach with a spherical grid has been employed to numerically model synthetic seismograms. Associated sensitivity kernels have also been constructed using a scattering integral method. Our preliminary results suggest the WSB is underlain by slow seismic velocities, with faster seismic structure beneath the adjacent Transantarctic Mountains and the Belgica Subglacial Highlands. This may indicate that the WSB is associated with a region of thinner lithosphere, possibly associated with prior continental rifting. The seismic heterogeneity highlighted in our model could have significant implications for understanding the geodynamic origin of WSB topography and its influence on ice-sheet behavior. 
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  2. Recent investigations in polar environments have examined solid-Earth-ice-sheet feedbacks and have emphasized that glacial isostatic adjustment, tectonic, and geothermal forcings exert first-order control on the physical conditions at and below the ice-bed interface and must be taken into account when evaluating ice-sheet evolution. However, the solid-Earth structure beneath much of Antarctica is still poorly constrained given the sparse distribution of seismic stations across the continent and the generally low seismicity rate. One region of particular interest is the Wilkes Subglacial Basin (WSB) in East Antarctica. During the mid-Pliocene warm period, the WSB may have contributed 3-4 m to the estimated 20 m rise in sea-level, indicating that this region could also play an important role in future warming scenarios. However, the WSB may have experienced notable bedrock uplift since the Pliocene; therefore, past geologic inferences of instability may not serve as a simple analogue for the future. Using records of ambient seismic noise recorded by both temporary and long-term seismic networks, along with a full-waveform tomographic inversion technique, we are developing improved images of the lithospheric structure beneath East Antarctica, including the WSB. Empirical Green’s Functions with periods between 40 and 340 s have been extracted using a frequency-time normalization technique, and a finite-difference approach with a spherical grid has been employed to numerically model synthetic seismograms. Associated sensitivity kernels have also been constructed using a scattering integral method. Our preliminary results suggest the WSB is underlain by slow seismic velocities, with faster seismic structure beneath the adjacent Transantarctic Mountains and the Belgica Subglacial Highlands. This may indicate that the WSB is associated with a region of thinner lithosphere, possibly associated with prior continental rifting. The seismic heterogeneity highlighted in our model could have significant implications for understanding the geodynamic origin of WSB topography and its influence on ice-sheet behavior. 
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  3. Abstract

    We develop a robust and simple rule‐based algorithm to autonomously simulate alluvial fan deposition and evolution under continuously developing landscape conditions without prescribing deposition locations or imposing topographic constraints. Augmented with this algorithm, landscape evolution models are capable of dynamically detecting locations of potential fan deposition by statistical measures of surface topography and fluvial dynamics, then depositing fan sediments where and when the developed conditions require. To assess the method's efficacy in depositing sediment at a mountain‐valley transition zone characterized by a transport surface that permits unobstructed exit of sediment and water, a hypothetical scenario is created that involves a frontal, normal fault. It is followed by a series of sensitivity analyses to ascertain the influence of parameters affecting fan deposition and secondary processes. Uplift (u) and precipitation significantly impact fan morphological characteristics, which are within the range of real‐world fans. Higher rates of each cause the notable expansion of the fan area except in cases of exceptionally high precipitation rates. Fan area has a power‐law relationship with most of the tested parameters, , where is erodibility (lithology), and are fluvial parameters, and is catchment area ( ~0.9). This study is the first showcasing fan power‐law relationships using numerical modelling. While fan area increases with precipitation, there exists a threshold beyond which fan area diminishes, and the formation of fans ceases altogether. The algorithm provides a basis for improving mechanistic understanding of fans by offering a robust platform for testing process dominance and scaling. The results demonstrate its applicability for landscape evolution simulation over a long time and broad spatial scales. We also investigate the hydrological significance of including autonomously generated alluvial fans in coupled landscape evolution—hydrology models that focus on groundwater as well as surface water hydrology.

     
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  4. Lateral heterogeneity in the upper mantle beneath Antarctica has important implications to understanding the response of the Earth to changes in ice mass loss and estimates of geothermal heat flow. As seismic coverage and employed methodologies improve, lateral variations have been found in regions that were once assumed to be relatively uniform. Here we present the results from a full-wave inversion constrained by long-period (40-340 s) empirical Green’s functions (EGFs) extracted by using a frequency-time normalization approach and cross-correlating several decades worth of ambient seismic noise. Using the computational resources at the Alabama Supercomputing Authority, we simulate waveforms within a spherical, finite-difference grid. Phase delays are then measured by cross-correlating the EGFs and synthetic waveforms, sensitivity kernels are constructed using the scattering integral method, and the model is iteratively inverted to obtain a refined upper mantle structure. Preliminary results from our continental-scale model not only emphasize lateral variations in West Antarctica that have been observed in some previous models but also highlight distinct mantle anomalies beneath East Antarctica, many of which were previously unresolved. We will present our final model for the whole of Antarctica, illustrating how mantle heterogeneities are associated with different tectonic terranes, providing further constraints for heat flow and ice-sheet modeling. 
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  5. null (Ed.)
    The origins of tectonic structures in East Antarctica, such as the Gamburtsev Subglacial Mountains (GSMs), the Wilkes Subglacial Basin (WSB), the Aurora Subglacial Basin (ASB), and the Transantarctic Mountains (TAMs), are not clearly understood. Previous investigations have proposed multiple origin models to explain the formation of these structures; however, existing tomographic images lack resolution and consistency given the sparse seismic coverage in East Antarctica. We use full-waveform ambient noise tomography to model the shear-wave velocity structure beneath East Antarctica to further investigate these features. We extract Rayleigh-wave Empirical Green’s Func-tions (EGFs) between periods of 15 and 340 secs from ambient seismic noise using a frequency time normalization technique. Synthetic waveforms are simulated through a 3-D heterogenous Earth model with a lateral grid spacing of 0.025º (~2.25 km) using a finite-difference wave propagation method. The synthetic seismograms are cross-correlated with the EGFs to measure the phase delays. The fi-nite-frequency sensitivity kernels are calculated using the scattering-integral approach and the shear-wave velocity model is computed by inverting the phase delays using a sparse damped least-square inversion method. Preliminary results show fast seismic velocities beneath the WSB, which may be associated with thick and stable lithosphere, and slow velocities beneath the ASB, possibly reflecting old rift systems or other inherited tectonic structures. Slow upper mantle velocities are also observed beneath the TAMs, possibly associated with a thermal load that contributes to the uplift of the moun-tain range. Slow shear-wave velocities in the vicinity of the GSMs may be associated with rifting along the extended Lambert Rift System. Our final tomographic model and associated tectonic inter-pretations will be shared. 
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  6. null (Ed.)
    The thick ice coverage and harsh climatic conditions in East Antarctica hinder detailed investigations of tectonic features, leading to debates regarding the origin and evolution of the Gamburtsev Subglacial Mountains (GSM), the Wilkes Subglacial Basin (WSB), the Aurora Subglacial Basin (ASB), and the Transantarctic Mountains (TAMs). Present tomographic models lack resolution and consistency given the minimal seismic coverage in East Antarctica. To further such investigations, we are using full-waveform ambient noise tomography to model shear-wave velocities and to constrain the crustal and upper mantle structure beneath East Antarctica. This approach utilizes Empirical Green’s functions (EGFs), which provides information about the Earth structure between recording stations and is an alternative approach compared to many traditional tomographic models. EGFs from ambient seismic noise between periods of 15-340 secs are extracted using a frequency-time normalization approach, and synthetic waveforms are simulated through a three-dimensional heterogeneous Earth model using a finite-difference wave propagation method with a grid spacing of 0.025º (~ 2.25 km). Phase delays are computed by cross correlating EGFs and the synthetics, and sensitivity kernels are constructed using a scattering integral approach. Preliminary results show slow velocities beneath both the WSB and ASB, possibly reflecting old rift systems or other inherited tectonic structures. A transition from slow to fast velocities beneath the Northern Victoria Land portion of the TAMs is consistent with thermal loading beneath the mountain range. Slow velocities beneath the GSM may be due to rifting associated with the extended Lambert Rift System. These preliminary results are currently being updated using a larger EGF dataset; our final model will be used to assess East Antarctic tectonic structures and to resolve the ambiguity associated with their origin models. 
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  7. The origin and tectonic evolution of various features in East Antarctica, such as the Wilkes Subglacial Basin (WSB), Aurora Subglacial Basin (ASB), Transantarctic Mountains (TAMs), and Gamburtsev Subglacial Mountains (GSM), are unconstrained due to thick ice coverage and a lack of direct geologic samples. We are modeling the crustal and upper mantle structure beneath these areas using a full-waveform tomography method to further our understanding the tectonic evolution of the continent as well as the behavior of the overlying ice sheet. A frequency-time normalization approach is employed to extract empirical Green’s functions (EGFs) from ambient seismic noise, between periods of 15-340 seconds. EGF ray path coverage is dense throughout East Antarctica, indicating that our study will provide new, high resolution imaging of this area. Synthetic waveforms are simulated through a three-dimensional heterogeneous Earth model using a finite-difference wave propagation method with a grid spacing of 0.025º, which accurately reproduces Rayleigh waves at 15+ seconds. Following this, phase delays are measured between the synthetics and the data, sensitivity kernels are constructed using the scattering integral approach, and we invert using a sparse, least-squares method. Preliminary results show that slow velocities are present beneath both the WSB and ASB, possibly indicating old rift systems or other inherited tectonic structures. The transition from slow to fast velocities beneath the Northern Victoria Land section of the TAMs is consistent with thermal loading beneath the mountain range. The presence of slow velocities near the GSM may be associated with rifting along the Lambert Rift System. 
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  8. null (Ed.)
    The origin and tectonic evolution of various features in East Antarctica, such as the Wilkes Subglacial Basin (WSB), Aurora Subglacial Basin (ASB), Transantarctic Mountains (TAMs), and Gamburtsev Subglacial Mountains (GSM), are unconstrained due to thick ice coverage and a lack of direct geologic samples. We are modeling the crustal and upper mantle structure beneath these areas using a full-waveform tomography method to further our understanding the tectonic evolution of the continent as well as the behavior of the overlying ice sheet. A frequency-time normalization approach is employed to extract empirical Green’s functions (EGFs) from ambient seismic noise, between periods of 15-340 seconds. EGF ray path coverage is dense throughout East Antarctica, indicating that our study will provide new, high resolution imaging of this area. Synthetic waveforms are simulated through a three-dimensional heterogeneous Earth model using a finite-difference wave propagation method with a grid spacing of 0.025º, which accurately reproduces Rayleigh waves at 15+ seconds. Following this, phase delays are measured between the synthetics and the data, sensitivity kernels are constructed using the scattering integral approach, and we invert using a sparse, least-squares method. Preliminary results show that slow velocities are present beneath both the WSB and ASB, possibly indicating old rift systems or other inherited tectonic structures. The transition from slow to fast velocities beneath the Northern Victoria Land section of the TAMs is consistent with thermal loading beneath the mountain range. The presence of slow velocities near the GSM may be associated with rifting along the Lambert Rift System. 
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  9. Abstract The Transantarctic Mountains (TAMs), Antarctica, exhibit anomalous uplift and volcanism and have been associated with regions of thermally perturbed upper mantle that may or may not be connected to lower mantle processes. To determine if the anomalous upper mantle beneath the TAMs connects to the lower mantle, we interrogate the mantle transition zone (MTZ) structure under the TAMs and adjacent parts of East Antarctica using 12,500+ detections of P-to-S conversions from the 410 and 660 km discontinuities. Our results show distinct zones of thinner-than-global-average MTZ (∼205–225 km, ∼10%–18% thinner) beneath the central TAMs and southern Victoria Land, revealing throughgoing convective thermal anomalies (i.e., mantle plumes) that connect prominent upper and lower mantle low-velocity regions. This suggests that the thermally perturbed upper mantle beneath the TAMs and Ross Island may have a lower mantle origin, which could influence patterns of volcanism and TAMs uplift. 
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