Preprints
https://doi.org/10.5194/egusphere-2022-1363
https://doi.org/10.5194/egusphere-2022-1363
 
12 Dec 2022
12 Dec 2022
Status: this preprint is open for discussion.

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

Nikolas Aleksi Ovaskainen1,2, Pietari Mikael Skyttä2, Nicklas Johan Nordbäck1,2, and Jon Oskar Engström1 Nikolas Aleksi Ovaskainen et al.
  • 1Geological Survey of Finland, P.0. Box 96, Espoo, FI-02151, Finland
  • 2University of Turku, Department of Geography and Geology, Finland

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.

Nikolas Aleksi Ovaskainen et al.

Status: open (extended)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on egusphere-2022-1363', Matthis Frey, 28 Dec 2022 reply
    • AC1: 'Reply on CC1', Nikolas Ovaskainen, 02 Jan 2023 reply
  • RC1: 'Comment on egusphere-2022-1363', Anonymous Referee #1, 10 Jan 2023 reply

Nikolas Aleksi Ovaskainen et al.

Nikolas Aleksi Ovaskainen et al.

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Short summary
We have studied fracturing of the bedrock at Åland Islands from bedrock outcrops and digital elevation models using multiple scales of observation. Using the results we can compare properties of the fractures of different sizes to find similarities and differences. E.g., we found that glacial erosion has probable effect on the study of larger bedrock structures. Furthermore, we collected data from 100 to 500 m long fractures which have previously been proven to be difficult to sample.