A semi-automated algorithm to quantify scarp morphology (SPARTA): Application to normal faults in southern Malawi

Michael Hodge*, Juliet Biggs, Åke Fagereng, Austin Elliott, Hassan Mdala, Felix Mphepo

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)

8 Citations (Scopus)
320 Downloads (Pure)

Abstract

Along-strike variation in scarp morphology reflects differences in a fault's geomorphic and structural development and can thus indicate fault rupture history and 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 digital elevation model (DEM) resolutions. We then apply our new algorithm to a 12m resolution TanDEM-X DEM for four southern Malawi fault scarps, located at the southern end of the East African Rift system: the Bilila-Mtakataka fault (BMF) and three previously unreported scarps-Thyolo, Muona and Malombe. All but Muona exhibit first-order structural segmentation at their surface. By using a 5m resolution DEM derived from high-resolution (50cmpixel-1) Pleiades stereo-satellite imagery for the Bilila-Mtakataka fault scarp, we quantify secondary structural segmentation. Our scarp height calculations from all four fault scarps suggest that if each scarp was formed by a single, complete rupture, the slip-length ratio for each earthquake exceeds the maximum typical value observed in historical normal faulting earthquakes around the world. The high slip-length ratios therefore imply that the Malawi fault scarps likely formed in multiple earthquakes. The scarp height distribution 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 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.

Original languageEnglish
Pages (from-to)27-57
Number of pages31
JournalSolid Earth and Discussions
Volume10
Issue number1
Early online date11 Jan 2019
DOIs
Publication statusPublished - Jan 2019

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