A new subsampling methodology to optimize the characterization of two-dimensional bedrock fracture networks

Ovaskainen, Nikolas; Nordbäck, Nicklas; Skyttä, Pietari; Engström, Jon

doi:10.1016/j.jsg.2022.104528

Cited by 13 publications

(28 citation statements)

References 53 publications

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“…The fracture traces that represent the outcrop scale data within this study, are from the northern shoreline of Getaberget (Figure 1), where recent contributions have revealed that the Åland Batholith was subjected to brittle faulting and generation of associated fracture systems (Ovaskainen et al, 2022;Skyttä et al, 2022). The observed fractures comprise joints, extension fractures, veins and faults, which display a range of lengths from a few cm to 200 m. Outside larger fault zones, joints are arranged in three mutually orthogonal sets with roughly N-S and E-W sub-vertical and sub-horizontal orientation.…”

Section: Geological Settingmentioning

confidence: 99%

“…We used existing fracture trace data published by (Ovaskainen et al, 2022) from the northern shore of Åland Islands as the outcrop scale 1:10 dataset (Figure 2). The fracture data was collected from 2D raster orthophotos from within 13 circular target areas along the E-W trending Getaberget shoreline.…”

Section: Datamentioning

confidence: 99%

“…However, rather than investigating each target area individually we merge the trace data (n=42499) into a single dataset of traces that are cropped specifically to the associated target areas resulting in a trace count of 41544. There are significant variations in fracture network properties between the target areas but without apparent spatial trends that could be used to correlate the characteristics with their location (Ovaskainen et al, 2022). Therefore, the merging of the data produces an aggregated dataset of the fracture characteristics, representative for the entire Getaberget shoreline study area.…”

Section: Datamentioning

confidence: 99%

“…Similar to Ovaskainen et al (2022), we used the snapping functionality present in both software packages in order to honor the true abutment relationship between the traces, and consequently, document realistic topological relationships of the network (Nyberg et al, 2018). To verify the topological consistency of the lineaments the traces are validated with a Python package, FRACTOPO, which provides a validation utility to find e.g., V-nodes and overlapping lineament sections (Ovaskainen, 2022b).…”

Section: Datamentioning

confidence: 99%

“…We conducted mapping of brittle bedrock structures in three different scales of observation, outcrop, semi-regional and regional scale and using a combination of comparable remote-sensing methods. As the outcrop scale data (scale of observation circa 1:10) we used fracture trace data published in Ovaskainen et al (2022) which contains fractures with lengths from centimeters to roughly 30 m. The available trace data was originally digitised from orthomosaics spanning an area of circa 20700 m 2 . For the semi-regional scale (ca.…”

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confidence: 99%

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Detailed investigation of multi-scale fracture networks in glacially abraded crystalline bedrock at Åland Islands, Finland

Ovaskainen

Skyttä²,

Nordbäck³

et al. 2022

Preprint

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Abstract. Using multiple scales of observation in studying the fractures of the bedrock increases the reliability and representativeness of the respective studies. This is because the discontinuities, i.e., the fractures, in the bedrock lack any characteristic length and instead occur within a large range of scales of approximately 10 orders of magnitude. Consequently, fracture models need to be constructed based on representative multi-scale datasets to enable valid interpolation and extrapolation of common scaling laws to all fracture sizes. In this paper, we combine a detailed bedrock fracture study from an extensive bedrock outcrop area with lineament interpretation using Light Detection And Ranging (LiDAR) and geophysical data. Our study offers lineament data in an intermediary length range missing from Discrete Fracture Network -modelling conducted at Olkiluoto, a nuclear spent fuel facility in Finland. In addition, this study also provides a robust multi-scale fracture and lineament dataset which has been thoroughly analysed for the purposes of understanding the uncertainties and differences in the different datasets. Our analysis further covers the topological, scale-independent, fracture network characteristics. Results of our study include the discovery of three distinct azimuth sets, N-S, NE-SW and WNW-ESE, both single scale and multi-scale power-law models for fracture and lineaments and further insight into a trend of decreasing apparent connectivity of fracture networks as the scale of observation increases. Specifically, a multi-scale power-law exponent of -1.13 is fitted to fracture and lineament lengths although we found that individually the fractures and lineaments might follow distinct power-laws rather than a common one.

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Section: Geological Settingmentioning

confidence: 99%

Section: Datamentioning

confidence: 99%

Section: Datamentioning

confidence: 99%

Section: Datamentioning

confidence: 99%

mentioning

confidence: 99%

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Detailed investigation of multi-scale fracture networks in glacially abraded crystalline bedrock at Åland Islands, Finland

Ovaskainen

Skyttä²,

Nordbäck³

et al. 2022

Preprint

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The interplay of bedrock fractures and glacial erosion in defining the present‐day land surface topography in mesoscopically isotropic crystalline rocks

Skyttä

Nordbäck

Ojala

et al. 2023

Earth Surf Processes Landf

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This paper addresses the effect of fractures within crystalline bedrock on glacial erosion processes in fast flowing hard bed glacier environments. In particular, we examine (i) whether the fracture type is critical for the capability of a glacier to erode the bedrock through quarrying/plucking processes and (ii) whether we can recognize specific fracture‐controlled erosion signatures from bedrock surface morphologies. We conducted an investigation within the northern part of the Åland Islands, southern Finland, where the ice‐flow direction (N–S) has remained constant through Late Pleistocene glaciations and where the bedrock is characterized by a lack of any mesoscopic anisotropies (such as foliation) and hence provides an optimal target to recognize the relationships between fractures and erosional morphologies. We characterized the fracture systems within the bedrock using both UAV‐acquired orthophotographs and standard field approaches and extrapolated the results to larger scales using LiDAR‐based digital elevation models. Our findings indicate that individual joints or shear fractures are associated with the development of minor vertical breaks along the bedrock surface. However, they do not provide sufficient mechanical weakness zones in the bedrock to allow effective glacial quarrying, even though their lengths can be relatively large (>50 m). By contrast, the linkage of several parallel shear fractures or the presence of larger faults with gouge‐bearing cores and well‐developed damage zones leads to localized disintegration of the rock material and the subsequent development of distinct topographic depressions along the bedrock surface. Consequently, the results allow predictions to be made about the bedrock features underlying the observed topographic signatures along the bedrock surface. Applied to the area of this investigation, abrasion associated with N–S‐directed glacial flows is responsible for the N–S‐oriented elongate but smooth fjord‐like megagrooves, whereas the more abrupt topographic breaks were generated by quarrying controlled by sub‐vertical, E–W‐trending zones of localized brittle deformation.

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Automated mapping of bedrock-fracture traces from UAV-acquired images using U-Net convolutional neural networks

Chudasama,

Ovaskainen,

Tamminen

et al. 2024

Computers & Geosciences

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A new subsampling methodology to optimize the characterization of two-dimensional bedrock fracture networks

Cited by 13 publications

References 53 publications

Detailed investigation of multi-scale fracture networks in glacially abraded crystalline bedrock at Åland Islands, Finland

Detailed investigation of multi-scale fracture networks in glacially abraded crystalline bedrock at Åland Islands, Finland

The interplay of bedrock fractures and glacial erosion in defining the present‐day land surface topography in mesoscopically isotropic crystalline rocks

Automated mapping of bedrock-fracture traces from UAV-acquired images using U-Net convolutional neural networks

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