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Discussion papers
https://doi.org/10.5194/se-2018-38
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/se-2018-38
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 09 May 2018

Research article | 09 May 2018

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Solid Earth (SE).

A Semi-Automated Algorithm to Quantify Scarp Morphology (SPARTA): Application to Normal Faults in Southern Malawi

Michael Hodge1,5, Juliet Biggs2,5, Åke Fagereng1,5, Austin Elliott3,5, Hassan Mdala4, and Felix Mphepo4 Michael Hodge et al.
  • 1School of Earth and Ocean Sciences, Cardiff University, Cardiff, UK
  • 2School of Earth Sciences, University of Bristol, Bristol, UK
  • 3Department of Earth Sciences, University of Oxford, Oxford, UK
  • 4Geological Survey Department, Mzuzu Regional Office, Malawi
  • 5Centre for Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET)

Abstract. Along-strike variation in scarp morphology reflects differences in a fault's geomorphic and structural development and can thus indicate fault rupture history as well as mechanical segmentation. Parameters that define scarp morphology (height, width, slope) are typically measured or calculated manually. The time-consuming manual approach reduces the density and objectivity of measurements, and can lead to oversight of small-scale morphological variations that occur at a resolution impractical to capture. Furthermore, inconsistencies in the manual approach may also lead to unknown discrepancies and uncertainties between, and also within, individual fault scarp studies. Here, we aim to improve the efficiency, transparency and uniformity of calculating scarp morphological parameters by developing a semi-automated Scarp PARameTer Algorithm (SPARTA). We compare our findings against a traditional, manual analysis and assess the performance of the algorithm using a range of elevation model resolutions. We then apply our new algorithm to a 12m resolution DEM for four southern Malawi fault scarps, located at the southern end of the East African Rift System: the Bilila-Mtakataka fault and three previously unreported scarps – Thyolo, Muona and Malombe. All but Muona exhibit first-order structural segmentation at their surface, and by using a 5m resolution DEM derived from high-resolution stereo satellite imagery for the Bilila-Mtakataka fault scarp, we are able to quantify secondary structural segmentation. Our scarp height calculations from all four fault scarps suggests that if each scarp was formed by a single, complete rupture, the slip-length ratio for each fault exceeds the maximum typical value observed empirically in historical normal faulting earthquakes around the world, implying that their structural histories are more complex. The distribution of vertical displacement at the surface implies the structural segments of both the BMF and Thyolo fault have merged via rupture of discrete faults (hard-links) through several earthquake cycles, and the segments of the Malombe fault have connected via distributed deformation zones (soft-links). For all faults studied here, the length of earthquake ruptures may therefore exceed the constitutive length of each segment. Thus, our findings shed new light on the seismic hazard in southern Malawi, indicating evidence for a number of large (MW 7–8) prehistoric earthquakes, as well as providing a new semi-automated methodology (SPARTA) for calculating scarp morphological parameters, which can be used on other fault scarps to infer structural development.

Michael Hodge et al.
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Status: final response (author comments only)
Status: final response (author comments only)
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Michael Hodge et al.
Data sets

SPARTA Python examples M. Hodge https://doi.org/10.5281/zenodo.1236883

Model code and software

SPARTA Python code M. Hodge https://doi.org/10.5281/zenodo.1236883

Michael Hodge et al.
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Short summary
This work attempts to create a semi-automated algorithm (called SPARTA) to calculate height, width and slope of surface breaks produced by earthquakes on faults. We developed the algorithm using a series of synthetic catalogues, which can include noise-features such as vegetation, hills and ditches, which mimic natural environments. We then apply the algorithm to four fault scarps in southern Malawi, at the southern end of the East African Rift System, to understand their earthquake potential.
This work attempts to create a semi-automated algorithm (called SPARTA) to calculate height,...
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