Palaeoseismological investigation of active normal faults in Namibia: investigating stable continental region (SCR) seismicity and seismic hazard in southern Africa

• Applicant: Dr. Beth Kahle
• Subject Area: Geology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 560087224

Despite growing awareness that stable continental regions (SCRs) have higher seismic hazard than previously thought, these regions remain poorly studied in terms of their palaeoseismological record. Geomorphological evidence of geologically recent faulting in Namibia offers an opportunity to address this gap. Namibia, like most of Southern Africa, is considered an SCR with low strain rates and associated apparent low seismic hazard. Despite this, geomorphological evidence exists for large, geologically recent normal faulting earthquakes in the form of fault scarps. We have carried out preliminary remote sensing and field studies on the previously-known Hebron fault and documented for the first time a spatial clustering of scarps in the SW of Namibia. Earthquake scaling relationships suggest that these faults could fail in earthquakes with magnitudes greater than Mw 6.4 and perhaps greater than Mw 7.0. Unfortunately, geomorphological evidence for prehistoric earthquakes is not generally taken into account in seismic hazard assessments of the region, which instead rely solely on instrumental records. In areas of low strain rates, earthquake recurrence intervals are expected to be on the order of thousands to tens of thousands of years, or even longer, meaning that the instrumental record is unlikely to capture a true picture of seismic hazard. A recent seismic hazard assessment for the country estimates a maximum magnitude of Mw 5.3 in the vicinity of the Hebron fault which, we argue, is capable of generating earthquakes of Mw 7.1. Understanding the earthquake history of these scarps is therefore critical for providing more accurate estimates of seismic hazard in the region. We therefore propose two field campaigns to carry out palaeoseismological trenches on these faults. We intend to date, using C-14 and optically stimulated luminescence (OSL) dating, the most recent earthquake on the faults, estimate the magnitude of these events, as well as assessing evidence for multiple earthquakes. This will be the first study of this kind in the region. In addition to improving seismic hazard assessments, the study will also allow us to address fundamental questions in SCR seismicity such as: How large can continental normal faulting earthquakes actually be?; Do earthquakes in this low strain rate region occur through repeated slip on the same fault?; Do the earthquakes display temporal as well as spatial clustering? Since normal faulting SCR events are so rare in global catalogues, answers to these questions are of international interest and importance, but they also have direct relevance to local low strain rate regions, such as the Rhine graben. The semi-arid climate, low levels of anthropogenic modification, and slow erosion rates of the study region are likely to allow an unparalleled record of long-term seismicity. This makes it an understudied but internationally important natural laboratory to address these issues.

• DFG Programme: Research Grants
• International Connection: South Africa
• Co-Investigators: Professorin Anke Friedrich, Ph.D.; Privatdozent Dr. Simon Kübler
• Cooperation Partners: Dr. Khumo Leseane; Dr. Robert Muir; Professor Dr. Alastair Sloan