An effective-medium model for P-wave velocities of saturated, unconsolidated saline permafrost

Dou, Shan; Nakagawa, Seiji; Dreger, Douglas S.; Ajo‐Franklin, Jonathan

doi:10.1190/geo2016-0474.1

Cited by 33 publications

(41 citation statements)

References 48 publications

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“…Two-end member models. The SCA is suggested by Dou et al (2017) to calculate the bulk modulus K IF (Pa) and shear modulus G IF (Pa) for the fully frozen end member only composed of ice and soils:…”

Section: Appendix A: Key Equations In the Compared Modelsmentioning

confidence: 99%

Comparison of Geoacoustic Models for Unfrozen Water Content Estimation

et al. 2020

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This paper reviews eight geoacoustic models applied to frozen soils: crystal growth models (grain cementing, grain coating, matrix supporting, and pore filling), the weighted equation (WE) model, Zimmerman and King's model (KT), the Biot-Gassmann theory modified by Lee (BGTL), and a two-end member model. We verify the capacity of these models to estimate unfrozen water content (UWC) based on "reference" UWC results and joint P and S wave velocities for different soil types. The satisfactory UWC estimates of saline unconsolidated sand and overconsolidated clay based on V p data prove that the KT, BGTL, and two-end member models are capable of modeling "smooth" transitions in the ice crystal growth mode, while they may provide less accurate UWC values when abrupt change of crystallization mode occurs. None of the tested soil types show a single crystallization mode throughout the freezing process, as assumed by individual crystal growth models. V s-based UWC estimates are less accurate due to significant but difficult-to-estimate influence of effective stress and soil initial cementation. All models, except pore filling and matrix supporting, can match V s versus V p measurement results for sands and silts but gradually provide inconsistent estimates with increasing clay content. We conclude that model validation by independent UWC measurements is necessary and that consistency between UWC values estimated from V s and V p is insufficient to ensure proper model validation.

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Section: Appendix A: Key Equations In the Compared Modelsmentioning

confidence: 99%

Comparison of Geoacoustic Models for Unfrozen Water Content Estimation

et al. 2020

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“…This partially unfrozen, saline soil may be as shallow as 2 m bgs based on our core analysis, which has significant geomechanical and biogeochemical implications. Specifically, in addition to the significantly compromised mechanical strength of the saline permafrost shown in previous studies (Dou et al, 2016;Hivon & Sego, 1995;Nixon, 1987;Wu et al, 2017), slow yet continuous biogeochemical processes may occur in the unfrozen water, which are likely the cause of the significant shift of the geochemical characteristics of the deeper permafrost soils. We will discuss this later.…”

Section: 1002/2018jg004413mentioning

confidence: 87%

“…While recent studies have identified partially unfrozen soil below the permafrost table (Dafflon et al, 2016;Dou et al, 2016;Hubbard et al, 2013), the deeper permafrost that reaches an almost constant soil temperature around À9°C at 16 m bgs can be considered as continuous at the site (Jogenson et al, 2008). A shallow active layer with a thickness up to~50 cm (Gangodagamage et al, 2014;Hubbard et al, 2013) rests on top of the permafrost and thaws seasonally.…”

Section: Study Sitementioning

confidence: 99%

Depth‐Resolved Physicochemical Characteristics of Active Layer and Permafrost Soils in an Arctic Polygonal Tundra Region

Ulrich

Kneafsey

et al. 2018

JGR Biogeosciences

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Permafrost physicochemical parameters play a key role in controlling the response of permafrost carbon to climate change. We studied the physicochemical parameters of permafrost in an Arctic tundra region to evaluate (1) how soil parameters vary with depth and whether and how they are interrelated, (2) whether and how permafrost soil differs from its overlaying active layer, and (3) whether soil property‐depth relationships are different across geomorphic features (e.g., low, flat, and high centered polygons). We also explored the possible biogeochemical processes that led to these soil characteristics and how they may affect biogeochemical reactions upon permafrost thaw. We observed (1) consistent relationships between soil property and depth and between major parameters, (2) large contrasts of key soil parameters between active layer and permafrost, indicative of potentially different response of the permafrost carbon to warming when compared to the active layer, and (3) a correlation between soil hydraulic conductivity and topographic features that impacts soil hydrologic processes. Our analysis suggests that the permafrost has a marine‐derived chemical signature that differs from the active layer and shapes the physicochemical fingerprints of the different geomorphic features. Specifically, we revealed the unique signatures of the high center polygons, indicative of possible microbial activity at depth (>1 m). Our study suggested consistent key soil parameter‐depth correlations while demonstrating complex lateral and vertical variabilities. These results are valuable for identifying approaches to upscale point‐based measurements and for improving model parameterization to predict permafrost carbon behavior and feedback under future climate.

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“…In our case, we will consider isotropic sediments, which then elastically are fully characterized by the bulk modulus K and the shear modulus µ. We use a rock physics model similar to the two-end member mixing approach used by Minshull, et al [28] and Dou, et al [29] that inherently assumes cementing and pore-filling ice forming simultaneously at all ice saturations. We compute elastic properties of a fully unfrozen composite (θ i = 0) by first using Hertz-Mindlin contact theory [30] to compute dry rock properties, and subsequently Gassmann fluid substitution [31] to compute fully water-saturated rock properties.…”

Section: Modeling Effects Of Thawing On Seismic Propertiesmentioning

confidence: 99%

Potential Use of Time-Lapse Surface Seismics for Monitoring Thawing of the Terrestrial Arctic

2020

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The terrestrial Arctic is warming rapidly, causing changes in the degree of freezing of the upper sediments, which the mechanical properties of unconsolidated sediments strongly depend upon. This study investigates the potential of using time-lapse surface seismics to monitor thawing of currently (partly) frozen ground utilizing synthetic and real seismic data. First, we construct a simple geological model having an initial temperature of −5 °C, and infer constant surface temperatures of −5 °C, +1 °C, +5 °C, and +10 °C for four years to this model. The geological models inferred by the various thermal regimes are converted to seismic models using rock physics modeling and subsequently seismic modeling based on wavenumber integration. Real seismic data reflecting altered surface temperatures were acquired by repeated experiments in the Norwegian Arctic during early autumn to mid-winter. Comparison of the surface wave characteristics of both synthetic and real seismic data reveals time-lapse effects that are related to thawing caused by varying surface temperatures. In particular, the surface wave dispersion is sensitive to the degree of freezing in unconsolidated sediments. This demonstrates the potential of using surface seismics for Arctic climate monitoring, but inversion of dispersion curves and knowledge of the local near-surface geology is important for such studies to be conclusive.

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An effective-medium model for P-wave velocities of saturated, unconsolidated saline permafrost

Cited by 33 publications

References 48 publications

Comparison of Geoacoustic Models for Unfrozen Water Content Estimation

Comparison of Geoacoustic Models for Unfrozen Water Content Estimation

Depth‐Resolved Physicochemical Characteristics of Active Layer and Permafrost Soils in an Arctic Polygonal Tundra Region

Potential Use of Time-Lapse Surface Seismics for Monitoring Thawing of the Terrestrial Arctic

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