Permafrost Characterization Using Dual Rayleigh Wave Analysis
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Solution Overview
Problem
Existing methods for characterizing permafrost properties, such as thickness, ice content, and mechanical properties, are inaccurate and unreliable due to high resistivity gradients and signal attenuation, particularly in seismic testing, leading to misleading interpretations.
Innovation Solution
A non-invasive seismic surface wave technique utilizing two distinct Rayleigh waves (R1 and R2) to quantify permafrost properties by determining relationships between these waves, allowing for independent characterization of physical properties like unfrozen water content, ice content, and porosity without assuming mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If electrical resistivity tomography (ERT) is used to detect pore-ice or segregated ice in permafrost, then ice content can be qualitatively detected based on electrical conductivity correlation, but the inversion results become less reliable at high resistivity gradients and differentiation between ice and certain geomaterials becomes highly uncertain
Solution Approach 1:
The patent introduces seismic surface wave techniques as an intermediary method to bridge the gap between electrical conductivity measurements and reliable permafrost characterization. By using seismic waves that propagate through the subsurface and are sensitive to mechanical properties, the method provides an alternative pathway to detect ice content and permafrost conditions without relying solely on electrical resistivity inversion, thereby resolving the reliability issue at high resistivity gradients
Solution Approach 2:
The patent changes the measurement parameter from electrical conductivity to seismic wave propagation characteristics. By measuring shear wave velocity and other seismic parameters that are directly influenced by the mechanical state of permafrost, the method avoids the inversion uncertainties associated with electrical resistivity while maintaining sensitivity to ice content and permafrost thickness
2Measurement precision
If ground penetrating radar (GPR) is used to map the thickness of the active layer, then active layer thickness can be detected, but the application is limited to shallow penetration depth due to signal attenuation and high electromagnetic noise in ice and water
Solution Approach 1:
The patent replaces the electromagnetic-based GPR system with a seismic wave-based system. Seismic waves, particularly surface waves, can penetrate much deeper into the subsurface compared to electromagnetic waves in conductive media. The seismic method uses mechanical wave propagation that is less attenuated by ice and water, enabling deep penetration while maintaining detection precision for active layer thickness and permafrost base identification
3Measurement precision
If conventional seismic testing is used to map the permafrost layer based on shear wave velocity measurement, then permafrost layer can be mapped, but the detection becomes inaccurate at high resistivity gradients and mechanical properties assumptions are required
Solution Approach 1:
The patent segments the seismic wave analysis into distinct components, particularly separating surface wave analysis from body wave analysis. By focusing on surface wave dispersion characteristics that are sensitive to shallow subsurface mechanical properties, the method provides accurate permafrost layer detection without requiring assumptions about deep mechanical properties. The segmentation allows targeted analysis of the active layer and permafrost base interface
Solution Approach 2:
The patent applies partial action by focusing seismic measurements specifically on surface wave propagation rather than attempting to characterize all wave types and full subsurface volume. This targeted approach on surface waves provides sufficient information for permafrost detection and characterization without the complexity and assumptions required for complete mechanical property modeling of the entire subsurface
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method provides accurate quantification of permafrost properties, reducing inversion difficulties and enhancing model stability, enabling precise determination of permafrost thickness, ice content, and mechanical properties like shear modulus and bulk modulus.
Implementation Method 1
with at least one vibratory source, emitting an input wave signal into the subsurface structure to cause generation of seismic wave signals in the subsurface structure
Implementation Method 2
with at least one receiver, acquiring and measuring the seismic wave signals from the subsurface structure
Implementation Method 3
surface wave signals comprise at least one first Rayleigh wave (R1) signal and at least one second Rayleigh wave (R2) signal associated with the region of interest
Data Source
AI summary
A method of quantifying a plurality of parameters of a subsurface structure comprising a region of interest, the method comprising the steps of: with at least one vibratory source, emitting an input wave signal into the subsurface structure to cause generation of seismic wave signals in the subsurface structure; with at least one receiver, acquiring and measuring the seismic wave signals from the subsurface structure, wherein the seismic wave signals comprise at least one first Rayleigh wave (R1) signal and at least one second Rayleigh wave (R2) signal associated with the region of interest; generating, at a data processing apparatus, seismic data associated with measurements of the seismic wave signals; determining, at the data processing apparatus, from the seismic data a relationship between the Rayleigh wave (R1, R2) signals, wherein the Rayleigh wave (R1, R2) signals are dependent on at least one of the plurality of parameters.