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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 27 Jun 2019

Research article | 27 Jun 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Solid Earth (SE).

Structure of massively dilatant faults in Iceland: lessons learned from high resolution UAV data

Christopher Weismüller1, Janos L. Urai2, Michael Kettermann2,a, Christoph von Hagke2,3, and Klaus Reicherter1 Christopher Weismüller et al.
  • 1Institute of Neotectonics and Natural Hazards, RWTH Aachen University, Aachen, 52074, Germany
  • 2Institute of Structural Geology, Tectonics and Geomechanics, RWTH Aachen University, Aachen, 52074, Germany
  • 3Institute of Geology & Paleontology, RWTH Aachen University, Aachen, 52074, Germany
  • anow at: Department of Geodynamics and Sedimentology, University of Vienna, Althanstraße 14, 1090 Vienna, Austria

Abstract. Normal faults in basalts develop massive dilatancy up to several tens of meters close to the Earth's surface and show corresponding interactions with groundwater and lava flow. These massively dilatant faults (MDF) are widespread in extensional settings like Iceland or the East African Rift, but their detailed geometry is not well understood, despite their importance for fluid flow in the subsurface, geohazards or geothermal energy. We present a large set of digital elevation models (DEM) of the surface geometries of MDF with 5–15 cm resolution, acquired along the Icelandic Rift zone using unmanned aerial vehicles (UAV). UAV provide a much higher resolution than aerial/satellite imagery and a much better overview than ground-based fieldwork, thus bridging the gap between outcrop scale and regional observations.

Our data present representative outcrops of MDF, formed in basaltic sequences linked to the Mid Ocean Ridge. We acquired photosets of overlapping images along about 20 km of MDF and processed these using photogrammetry to create high resolution DEMs and ortho-rectified images. We use this dataset to map the faults and their damage zones to measure length, opening width and vertical offset of the faults and identify surface tilt in the damage zones. Ground truthing of the data was done by field observations.

Mapped vertical offsets show typical trends of normal fault growth by segment coalescence. However, opening widths in map-view show variations at much higher frequency, caused by segmentation, collapsed relays and tilted blocks. These effects cause a commonly higher than expected ratio of vertical offset and opening width for a steep normal fault at depth.

Based on field observations and the relationships of opening width and vertical offset, we define three endmember morphologies of MDF: (i) dilatant faults with opening width and vertical offset, (ii) tilted blocks (TB), and (iii) opening mode (mode I) fissures. Field observation of normal faults without visible opening invariably shows that these have an opening filled by recent sediment. TB dominated normal faults tend to have a largest opening width with respect to vertical offsets. Fissures have opening widths up to 15 m with throw below a 2 m threshold. Plotting opening width versus vertical offset of the fractures shows that there is a continuous transition between the endmembers. We conclude that fractures associated with MDF belong to one larger continuum and the three endmembers are thus not necessarily indicative for fracture maturity.

Christopher Weismüller et al.
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Christopher Weismüller et al.
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Short summary
We use drones to study surface geometries of massively dilatant faults (MDF) on Iceland, with apertures of tens of meters at the surface. Based on throw, aperture and structures, we define three geometrically different endmembers of the surface expression of MDF and show that these belong to one continuum. The transition between the endmembers is fluent and can change at one fault over short distances, implying a less distinct control of deeper structures on surface geometries than expected.
We use drones to study surface geometries of massively dilatant faults (MDF) on Iceland, with...