Strukturelle Charakterisierung und Datierung einer aktiven Seitenverscheibung, die von Festgestein in unverfestigte Sedimente übergeht
Zusammenfassung der Projektergebnisse
Fault branching and splaying are common processes during the growth of faults, but not yet fully understood. One potential driver may be the passage of a fault through different materials. In this project we investigated fault branching on South Island, New Zealand. Based on a GPR survey at the Awatere Fault (location Saxton River) and analogue models, we analysed the structural style of a strike-slip fault that passes from bedrock to sediments and how this promotes fault branching and splaying. The GPR sections in the bedrock show that there is only a low number of faults developed (2 to 3) that are closely spaced, with distances between the individual faults in a range of 10 m to 20 m. At the point where the Awatere Fault passes into the unconsolidated alluvial deposits of the Saxton River valley, the number of faults successively increases to up to seven faults (based on a DEM analysis, the number is higher, with up to 10 faults) and also the spacing between the individual faults increases (distances between the faults are in a range of 5 m to 40 m over a zone of 150 m width). To replicate the situation at the Saxton River site, we conducted a series of analogue models to test the effect of lateral changes in rock properties (e.g., lithological boundaries) on the geometry of developing strike-slip faults. Our analogue model setup uses corn starch to represent bedrock and trapezoidal sand bodies of different size that represent less-consolidated sedimentary basins above the basement. The analogue models show that with increasing thickness of the sand bodies, the lateral changes in material properties play an increasing role; two fault branches form at the material boundaries, and remain active for the duration of fault slip in the model. The position of fault branch point is controlled by the material change. The flower-structures that develop during the analogue modelling are commonly wider for thicker than for thinner sand packages, which underlines the influence of the material properties on the geometry of the evolving faults. The boundary faults of the flower-structures root in the starch and propagate to the surface of the model, and they have therefore a helicoidal geometry. The results of this study have wide application to all active strike-slip faults that run into sedimentary basins, as is e.g., the case for the Newport-Inglewood Fault in the Los Angeles Basin. Furthermore, GPR surveys were conducted at the Hope Fault. At this location, the attenuation of GPR waves was very high, so that the penetration depth was not high enough to image fault structures properly. However, at the Hope Fault (location Greenburn Stream), we could identify a small basin structure and map its shape with a 3D GPR grid. Based on this information a small trench was dug and samples were taken for OSL dating. The basin structure could be either a sag pond or the remnant of an offset river channel. At the Hope, Hundelee and Alpine Faults, samples were taken from fault gouge material on which direct luminescence dating was performed. The natural feldspar luminescence signal from the Hope and Hundelee Faults was indistinguishable from saturation, whereas two samples from the Alpine Fault at Gaunt Creek yielded similar ages of 71 ± 6 ka and 55 ± 5 ka. While these ages significantly overestimate the date of the last event (AD 1717) due to partial thermal resetting, the study demonstrates that direct luminescence dating of fault gouge can be employed to estimate relative fault activity.
Projektbezogene Publikationen (Auswahl)
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Luminescence dating of active faults in New Zealand: First insights from pIRIR225. Deutsche Luminescence and Electron Spin Resonance Dating Conference (DLED), Innsbruck, Austria, 9 – 11th November 2023
Melo, A., Tsukamoto, S., Fuchs, M., Tanner, D., Brandes, C., Kroner, U. & Gloaguen, R.
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Direct dating of active faults using luminescence: A case of study in New Zealand. European Geosciences Union — General Assembly, Vienna, Austria, 14 – 19th April 2024
Melo, A., Tsukamoto, S., Fuchs, M., Tanner, D., Brandes, C., Kroner, U. & Gloaguen, R.
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Ground-Penetrating radar investigation of the Marlborough fault system, NZ. 84th Jahrestagung der Deutschen Geophysikalischen Gesellschaft, Friedrich-Schiller-Universität Jena, 10 – 14th March 2024
Igel, J., Brandes, C., Tanner, D.C., Tsukamoto, S. & Nicol, A.
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Lithology regulates the geometry of strike-slip faults. AGU Fall Meeting, Washington, 9 – 13th December 2024
Brandes, C., Tanner, D.C. & Nicol, A.
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Predicting the fault beneath a newly-created earthquake-related landform: A case study of Leader Fault rupture during the 2016 Kaikoura Earthquake, New Zealand. European Geosciences Union — General Assembly, Vienna, Austria, 14 – 19th April 2024
Tanner, D.C., Brandes, C., Nicol, A., Igel. J., Tsukamoto, S. & Rudmann, J.
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Lithological control on geometric complexity of active continental strike-slip faults – insight from GPR surveys and analogue modelling. Copernicus GmbH.
Brandes, Christian; Tanner, David; Igel, Jan & Nicol, Andrew
