the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 07 Jul 2025
Uncovering the deep structure of the Koillismaa Layered Intrusion Complex, Finland using a novel 3D seismic survey
Abstract. A pioneering ~22 km2 three-dimensional (3D) seismic survey was conducted in northeastern Finland within the SEEMS DEEP project to investigate the concealed Koillismaa Deep Intrusion (KDI), part of the 2.5–2.4 Ga Koillismaa–Näränkävaara Layered Intrusion Complex (KLIC). Utilizing low-cost piezoelectric nimble nodes and a single Vibroseis source, this survey represents one of the first 3D seismic investigations of a deep layered intrusion and its feeder system. The seismic data, supported by petrophysical measurements and synthetic modelling, reveal a complex internal architecture characterized by coherent reflectivity patterns indicative of modal layering. Interpretation suggests that the KDI is not a simple feeder but a more developed, chonolithic or funnel-tube-shaped intrusion. Integration of seismic data interpretation with gravity inversion and geological data enabled the construction of a Common Earth Model (CEM), which successfully reproduces the observed gravity anomaly. A major thrust fault, likely associated with the Oulujärvi Shear Zone, was imaged for the first time, offering new insights into the tectonic evolution and mineralization potential of the region. This study highlights the advances in 3D seismic methods in hardrock environment and establishes a methodological framework for future mineral exploration in similar geological settings.
Competing interests: Lead author is a member of the Solid Earth editorial board.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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RC1: 'Comment on egusphere-2025-3111', Anonymous Referee #1, 23 Jul 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-3111/egusphere-2025-3111-RC1-supplement.pdfCitation: https://doi.org/
10.5194/egusphere-2025-3111-RC1 -
AC1: 'Reply on RC1', Michal Malinowski, 27 Sep 2025
I would like to thank Reviewer 1 for a very positive evaluation of our manuscript. Most of the comments left in the annotated manuscript were implemented in the revised version.
Below, we add some additional explanation.
Regarding the comment on p.19, L316 on the “circular reasoning” related to the work of Deemer and Hurich. In fact, we first refer to the paper of Deemer & Hurich (1994), where the authors are performing the modelling of seismic response of mafic intrusions. In the commented sentence, we refer to a 1997 paper, where the authors specifically describe layered series of Sonkndal-Bjerkreim intrusion.
Regarding the comment about the Fresnel zone migration (p. 20, L344), we don’t specifically mention this type of migration, however the cited reference of Singh et al (2019) includes a comparison of standard Kirchhoff PreSDM and Fresnel Volume Migration.
On behalf of the authors,
Michal Malinowski
Citation: https://doi.org/10.5194/egusphere-2025-3111-AC1
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AC1: 'Reply on RC1', Michal Malinowski, 27 Sep 2025
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RC2: 'Comment on egusphere-2025-3111', Anonymous Referee #2, 29 Jul 2025
The work by Malinowski et al introduces the results of a newly acquired 3D seismic survey along thee known Koillismaa intrusion in Finland. The work starts with an overview of relevant references, compilation of existing petrophysical data to constrain the origin of reflectivity as seen in the 3D seismic results, along with incorporating existing density information and gravity inversion to validate the results further. The 3D results are incorporated together with 2D seismic and potential field inversion results acquired along the same site into a Common Earth Model of the site, offering new insight into its geological evolution, along with discussing the origin of reflectors seen in a broader sense.
Although 5D interpolation was used to improve the coherency of the reflections seen in the 3D seismic data, given the terrain difficulty, along with the authors themselves discussing the potential artifact zones introduced by this step, and as seen in the results themselves, I find this step relevant and appropriately applied and enhancing the reflectors with minimal artifact introduction.
Overall, I really enjoyed reading this paper and congratulate the authors on an excellent work. Besides very few technical comments, find it publication ready.
Keep up the good work!
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AC2: 'Reply on RC2', Michal Malinowski, 27 Sep 2025
I want to thank Reviewer 2 for a very positive evaluation of our manuscript. Most of the comments left in the annotated manuscript were implemented in the revised version.
Below, we add some additional explanation.
Comment on Figure 2. It is not possible to add the vertical axis, as the lithologies are roughly sorted by their depth occurrence. Still, they are repeated throughout the drillhole, e.g., diabase occurs at ca. 500-600 m depth, but also at ca. 900 and 1300 m depth.
Comment on the depth axis in Figure 3. The vertical axis shows “structural height”, which, in the case of the layered intrusions, is counted from the bottom of the layered series (see Karinen, 2010).
Comment on Figure 5: regarding the origin of "ringing" seen at approximately 125 Hz? We don’t have a clear answer to that. We can speculate that it is because of the sensor response, which is supposed to be flat till ca. 125 Hz. When merging the data, the system is by default applying a high-cut filter above 125 Hz; however, in our case, this filter was removed to improve the high-frequency response.
Comment on p. 15 regarding the work of Gislason et al. This is discussed in depth in a companion paper by Singh et al. 2025: there are similarities between the two collocated profiles shot in 2018 and 2023; however, the 2023 data show much more continuous reflections, and the overall data quality is much higher.
On behalf of the authors,
Michal Malinowski
Citation: https://doi.org/10.5194/egusphere-2025-3111-AC2
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AC2: 'Reply on RC2', Michal Malinowski, 27 Sep 2025
Status: closed
-
RC1: 'Comment on egusphere-2025-3111', Anonymous Referee #1, 23 Jul 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-3111/egusphere-2025-3111-RC1-supplement.pdf
-
AC1: 'Reply on RC1', Michal Malinowski, 27 Sep 2025
I would like to thank Reviewer 1 for a very positive evaluation of our manuscript. Most of the comments left in the annotated manuscript were implemented in the revised version.
Below, we add some additional explanation.
Regarding the comment on p.19, L316 on the “circular reasoning” related to the work of Deemer and Hurich. In fact, we first refer to the paper of Deemer & Hurich (1994), where the authors are performing the modelling of seismic response of mafic intrusions. In the commented sentence, we refer to a 1997 paper, where the authors specifically describe layered series of Sonkndal-Bjerkreim intrusion.
Regarding the comment about the Fresnel zone migration (p. 20, L344), we don’t specifically mention this type of migration, however the cited reference of Singh et al (2019) includes a comparison of standard Kirchhoff PreSDM and Fresnel Volume Migration.
On behalf of the authors,
Michal Malinowski
Citation: https://doi.org/10.5194/egusphere-2025-3111-AC1
-
AC1: 'Reply on RC1', Michal Malinowski, 27 Sep 2025
-
RC2: 'Comment on egusphere-2025-3111', Anonymous Referee #2, 29 Jul 2025
The work by Malinowski et al introduces the results of a newly acquired 3D seismic survey along thee known Koillismaa intrusion in Finland. The work starts with an overview of relevant references, compilation of existing petrophysical data to constrain the origin of reflectivity as seen in the 3D seismic results, along with incorporating existing density information and gravity inversion to validate the results further. The 3D results are incorporated together with 2D seismic and potential field inversion results acquired along the same site into a Common Earth Model of the site, offering new insight into its geological evolution, along with discussing the origin of reflectors seen in a broader sense.
Although 5D interpolation was used to improve the coherency of the reflections seen in the 3D seismic data, given the terrain difficulty, along with the authors themselves discussing the potential artifact zones introduced by this step, and as seen in the results themselves, I find this step relevant and appropriately applied and enhancing the reflectors with minimal artifact introduction.
Overall, I really enjoyed reading this paper and congratulate the authors on an excellent work. Besides very few technical comments, find it publication ready.
Keep up the good work!
-
AC2: 'Reply on RC2', Michal Malinowski, 27 Sep 2025
I want to thank Reviewer 2 for a very positive evaluation of our manuscript. Most of the comments left in the annotated manuscript were implemented in the revised version.
Below, we add some additional explanation.
Comment on Figure 2. It is not possible to add the vertical axis, as the lithologies are roughly sorted by their depth occurrence. Still, they are repeated throughout the drillhole, e.g., diabase occurs at ca. 500-600 m depth, but also at ca. 900 and 1300 m depth.
Comment on the depth axis in Figure 3. The vertical axis shows “structural height”, which, in the case of the layered intrusions, is counted from the bottom of the layered series (see Karinen, 2010).
Comment on Figure 5: regarding the origin of "ringing" seen at approximately 125 Hz? We don’t have a clear answer to that. We can speculate that it is because of the sensor response, which is supposed to be flat till ca. 125 Hz. When merging the data, the system is by default applying a high-cut filter above 125 Hz; however, in our case, this filter was removed to improve the high-frequency response.
Comment on p. 15 regarding the work of Gislason et al. This is discussed in depth in a companion paper by Singh et al. 2025: there are similarities between the two collocated profiles shot in 2018 and 2023; however, the 2023 data show much more continuous reflections, and the overall data quality is much higher.
On behalf of the authors,
Michal Malinowski
Citation: https://doi.org/10.5194/egusphere-2025-3111-AC2
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AC2: 'Reply on RC2', Michal Malinowski, 27 Sep 2025
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