EGU2020-1621
https://doi.org/10.5194/egusphere-egu2020-1621
EGU General Assembly 2020
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Structural analysis of the Theistareykir Fissure Swarm (NE Iceland) using field survey integrated with UAV-based - Structure from Motion techniques

Noemi Corti1 and Alessandro Tibaldi1,2
Noemi Corti and Alessandro Tibaldi
  • 1Department of Earth and Environmental Science, University of Milan-Bicocca, Milan, Italy
  • 2CRUST- Interuniversity Center for 3D Seismotectonics with Territorial Applications, Italy

Due to its position at the boundary between American and European plates, Iceland represents an ideal natural laboratory to study active rifting processes, where rifting mechanisms are complicated by the superimposition of tectonic and magmatic stresses. In order to contribute to the study of such processes, we focused our attention on the southern sector of the Theistareykir Fissure Swarm (ThFS), an active volcanic rift belonging to the Northern Volcanic Zone of Iceland, affected by both volcanic and seismic hazard.

We studied an area which is about 22 km2-large, situated 12 km south of the intersection of the ThFS with the Husavik Flatey Fault (HFF), a dextral strike-slip lineament belonging to the Tjornes Fracture Zone (TFZ). The area is characterized by the presence of normal faults and a dense swarm of extension fractures, affecting prevalently post-glacial, Holocene lavas, dated 8-10 and 11-12 ka. Only in the western sector of the area a Late Quaternary interglacial lava crops out, while the northeastern sector is covered by a Weichselian subglacial hyaloclastite. The southern sector of the area has been investigated with classical field survey, whereas in the northern part a 3.87 km2-large area has been reconstructed using the Structure from Motion (SfM) techniques, combined with an Unmanned Aerial Vehicle (UAV), obtaining orthomosaics, DSMs and 3D models with a centimetric resolution through 4189 UAV photos, collected in 7 different missions during summer 2018.

In the whole area, we recognized and mapped a total of 624 structures (comprising 583 extension fractures and 41 normal faults), and we took various measurements at 626 structural stations along extension fractures, and 132 along normal faults. Regarding extension fractures, we collected the strike and, in 441 cases where it was possible, the opening direction and the amount of opening; along normal faults we measured the strike, dip and vertical offset.

Our approach allowed to calculate stretch values across the rift comprised between 1.002 and 1.013, and an average opening direction value of 104.4°N, normal to the average extension fracture strike measured at the structural stations (14°N), suggesting a pure extensional opening in the studied area. Actually, in 281 cases out of our 441 stations along extension fractures we noticed a lateral component > 5°. Furthermore, 49% of data is not consistent with tectonics, neither with regard to the extensional fracture strike, nor with regard to opening directions. This suggests that stresses linked to regional tectonics are not the only cause of deformation, which could have been affected by different processes like dyke intrusion, deglaciation, and inflation/deflation of the Theistareykir volcano magma chamber.

How to cite: Corti, N. and Tibaldi, A.: Structural analysis of the Theistareykir Fissure Swarm (NE Iceland) using field survey integrated with UAV-based - Structure from Motion techniques, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1621, https://doi.org/10.5194/egusphere-egu2020-1621, 2019

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  • CC1: Comment on EGU2020-1621, Stefano Urbani, 06 May 2020

    Hi Noemi,
    congratulations for this interesting and stimulating work supported by a large amount of data. 
    I just want to ask for some questions/clarifications. 
    Which is the areal distribution within the fissure swarm of the extensional fractures not coherent with the regional tectonics? Is there any clustering in specific portions of the swarm? How far is the Theistareykir volcano from the swarm? Could the gravitational loading of the volcano be an additional possible process explaining the non coherent data?
    Thanks in advance for your answers.  
    Cheers

    Stefano

    • AC1: Reply to CC1, Noemi Corti, 07 May 2020

      Hi Stefano, thank you for your questions!

      Regarding areal distribution, in the complete work we related all the collected data (strike, opening direction and amount of opening along extension fractures) with latitude and longitude, obtaining a homogeneous spatial distribution for all data. Also distinguishing data coherent with tectonics and those which were not, we observed a homogeneous distribution of both datasets, so we can say that there is not a clustering in this specific area of the rift, which is situated 4 km south of the central volcano. If we consider the whole Theistareykir Fissure Swarm, instead, we can observe that going northward opening direction values tend to rotate clockwise, showing a predominance of right lateral component of opening; therefore a greater number of values non coherent with regional tectonics can be observed in the northern part of the rift, towards the sea cost. This northern sector has been described in detail by Bonali et al. (2019).

      Regarding the processes which can explain these non coherent data, firstly we have considered that the area is characterized by the presence of basaltic lava flows with similar thickness, so that we have excluded rheology effects. Furthermore, the geomorphological setting of the area, considering also the sector of the rift situated further north (where the low Theistareykir volcano is located) is mostly flat; the volcano, in fact, has an elevation of less than 100 m respect to the surrounding plain. Therefore, we have excluded also topography and gravitational loading effects. Instead, we have included processes of inflation/deflation of the volcano magma chamber as a possible cause of deformation, as it has been observed by Metzger and Jonsson (2014) between 2007 and 2009, when the area was affected by an uplift due to the inflation of the magma chamber.

      • CC2: Reply to AC1, Stefano Urbani, 07 May 2020

        Hi Noemi,

        thanks a lot for you answers.

        Keep going with this research!

        Best of luck!

        Cheers

        Stefano