Geomorphological evidence for seismic hazard on the southern edge of the Zimbabwe craton: The Kruger-Malale scarp, South Africa.

South Africa and its immediate surroundings are considered a stable continental region (SCR), characterized by minor seismicity and low strain rates on the order of 1x10 ^-9 yr ^-1. Such strain rates imply minimum recurrence intervals for major earthquakes of 10  - 100 Ka, or even longer. Consequently, the 50 - 70  year instrumental catalogues do not fully reflect the seismic risk potential of the region. Earthquakes in SCRs and slowly deforming regions can have large magnitudes, for example, the 2017 M_W 6.5 Moiyabana earthquake in Botswana and the 2006 M_W 7.0 Machaze earthquake in Mozambique, and occur in areas unprepared for large earthquakes. Given that such events occur infrequently, but appear to be widespread in the continents, it is important to understand the location, geological context and timing of such events and to assess where they may occur in the future. This can be addressed by investigating faults which show geomorphological evidence of neotectonic activity. We present an analysis of the Kruger-Malale scarp, located on the Bosbokspoort fault in the eastern Limpopo belt, South Africa. We applied stereophotogrammetry to aerial photographs from the Chief Directorate of the National Geo-Spatial Information (NGI) to generate a Digital Surface Model (DSM). Our results indicate that the Kruger-Malale scarp is a 55 km long composite scarp with an average cumulative throw of 9 m. We tentatively suggest that the most recent event had an average throw of 2 - 3 m. This structure has the potential to generate M_W 7.1 - 7.5 earthquakes. In combination with the 2017 M_W 6.5 Moiyabana earthquake in the western Limpopo belt, the Makgadikgadi Rifts in the Magondi belt, the Zambezi Rifts in the Zambezi belt, the Urema Rift in the Mozambique belt and the 2006 M_W 7.0 Machaze earthquake in the Mozambique belt there is evidence for extensional deformation completely surrounding the Zimbabwe craton, which appears to behave as a rheologically strong block concentrating strain within the actively (albeit slowly) deforming mobile belts that surround it.