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Abstract Half‐graben basins bounded by border faults typify early‐stage continental rifts. Deciphering the role that intra‐rift faults play in rift basin development is challenging as patterns of early‐stage faulting are commonly overprinted by subsequent deformation; yet the characterization of these faults is crucial to understand the fundamental controls on their evolution, their contribution to rift opening, and to assess their seismic hazard. By integrating multiple offshore seismic reflection data sets with age‐dated drill core, late‐Quaternary and cumulative faulting patterns are characterized in the Central and South Basins of the Malawi (Nyasa) Rift, an active, early‐stage rift system. Almost all intra‐rift faults offset a late‐Quaternary lake lowstand surface, suggesting they are active and should be considered in hazard assessments. Fault throw profiles reveal sawtooth patterns indicating segmented slip histories. Observed extension on intra‐rift faults is approximately twice that predicted from hanging wall flexure of the border fault, suggesting that intra‐rift faults accommodate a proportion of the regional extension. Cumulative and late‐Quaternary throws on intra‐rift faults are correlated with throw measured on the border fault in the Central Basin, whereas an anticorrelation is observed in the South Basin. Viewed in a regional context, these differences do not relate solely to the proposed southward younging of the rift. Instead, it is inferred that the distribution of extension is also influenced by variations in lithospheric structure and crustal heterogeneities that are documented along the rift axis.
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This content will become publicly available on February 1, 2026
Assessing Recency of Faulting in the Stable Continental Region of Western Cape, South Africa
ABSTRACT Field and desktop mapping studies were conducted for the stable continental region in the Western Cape Province of South Africa to characterize fault activity of four fault systems, including the Worcester, Groenhof, Piketberg-Wellington, and Colenso faults. The geologic studies presented here were in support of a Probabilistic Seismic Hazard Analysis (PSHA) for a nearby nuclear power facility site. Previous studies performed by the South African Council for Geoscience in the region suggested evidence of near-surface co-seismic deformation (De Beer, 2004; De Beer et al., 2008). The goal of this study is to re-assess the prior interpretations of these four faults and gather the required data for including them in a seismic source model for use in a PSHA. The primary aspects to include in the characterization are the recency of movement, slip rate, kinematics, and geometry. To improve the interpretation and target sites, the study used a satellite-derived digital elevation model and aerial imagery for six areas, totaling over 900 km2 of data. Limited Quaternary cover, or other late Cenozoic deposits that overlie the Precambrian and Paleozoic bedrock structures, resulted in difficulty constraining the recency of faulting. The new observations presented in this study suggest that reactivation and surface rupture along pre-Cenozoic faults of the four fault systems have not occurred in at least the last 10 ka. Further, the lack of youthful tectonic geomorphology and deformation of Quaternary stratigraphy indicate that surface faulting has not occurred in the late to middle Quaternary along any of these four structures.
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- Award ID(s):
- 2300560
- PAR ID:
- 10575963
- Publisher / Repository:
- Environmental & Engineering Geoscience
- Date Published:
- Journal Name:
- Environmental & Engineering Geoscience
- Volume:
- 31
- Issue:
- 1
- ISSN:
- 1078-7275
- Page Range / eLocation ID:
- 3 to 18
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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