The structural re-interpretation of the Lower Shire Basin in the Southern Malawi rift using gravity data

Chisenga, Chikondi; Dulanya, Zuze; Yan, Jianguo

doi:10.1016/j.jafrearsci.2018.08.013

Cited by 19 publications

(32 citation statements)

References 28 publications

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“…Thus, the identification and systematic mapping of active faults, which are then compiled with other fault attributes (e.g. slip rate and slip sense) into a geospatial active fault database, provide an important tool for assessing regional seismic hazard (Christophersen et al, 2015;Hart and Bryant, 1999;Langridge et al, 2016;Shyu et al, 2016;Styron et al, 2020;Styron and Pagani, 2020;Taylor and Yin, 2009). Not only can these databases provide information on Published by Copernicus Publications on behalf of the European Geosciences Union.…”

Section: Introductionmentioning

confidence: 99%

A systems-based approach to parameterise seismic hazard in regions with little historical or instrumental seismicity: active fault and seismogenic source databases for southern Malawi

et al. 2021

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Abstract. Seismic hazard is commonly characterised using instrumental seismic records. However, these records are short relative to earthquake repeat times, and extrapolating to estimate seismic hazard can misrepresent the probable location, magnitude, and frequency of future large earthquakes. Although paleoseismology can address this challenge, this approach requires certain geomorphic setting, is resource intensive, and can carry large inherent uncertainties. Here, we outline how fault slip rates and recurrence intervals can be estimated by combining fault geometry, earthquake-scaling relationships, geodetically derived regional strain rates, and geological constraints of regional strain distribution. We apply this approach to southern Malawi, near the southern end of the East African Rift, and where, although no on-fault slip rate measurements exist, there are constraints on strain partitioning between border and intra-basin faults. This has led to the development of the South Malawi Active Fault Database (SMAFD), a geographical database of 23 active fault traces, and the South Malawi Seismogenic Source Database (SMSSD), in which we apply our systems-based approach to estimate earthquake magnitudes and recurrence intervals for the faults compiled in the SMAFD. We estimate earthquake magnitudes of MW 5.4–7.2 for individual fault sections in the SMSSD and MW 5.6–7.8 for whole-fault ruptures. However, low fault slip rates (intermediate estimates ∼ 0.05–0.8 mm/yr) imply long recurrence intervals between events: 102–105 years for border faults and 103–106 years for intra-basin faults. Sensitivity analysis indicates that the large range of these estimates can best be reduced with improved geodetic constraints in southern Malawi. The SMAFD and SMSSD provide a framework for using geological and geodetic information to characterise seismic hazard in regions with few on-fault slip rate measurements, and they could be adapted for use elsewhere in the East African Rift and globally.

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Section: Introductionmentioning

confidence: 99%

A systems-based approach to parameterise seismic hazard in regions with little historical or instrumental seismicity: active fault and seismogenic source databases for southern Malawi

et al. 2021

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“…In this paper, we analyse the Thyolo fault, the border fault of the Lower Shire Graben in southern Malawi (Figure 1). The fault is an ideal location to study the effects of pre-existing structures on fault geometry and structure as the graben has a welldocumented polyphase history of extension (Castaing, 1991;Chisenga et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

Structural inheritance and border fault reactivation during active early-stage rifting along the Thyolo fault, Malawi

Wedmore

Williams

Biggs

et al. 2020

Journal of Structural Geology

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Highlights • The Thyolo fault, Malawi, is a rift border fault with a polyphase tectonic history • Satellite and field data confirm recent activity on an 18.6 ± 7.7 m high scarp • The fault is segmented, but scarp height minima do not align with geometry changes • Pre-existing shallow structures control the surface geometry and 0.7 m wide fault core • Fault displacement is affected by viscous reactivation along a terrane boundary

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“…These surveys were used to refine fault mapping in cases where features interpreted as faults in the aeromagnetic survey extended beyond their surface expression. A revised fault map for the Lower Shire Graben based on gravity surveys (Chisenga et al, 2018) was also consulted when compiling the SMAFD.…”

Section: Geophysical Datasetsmentioning

confidence: 99%

“…There are significant uncertainties in estimating sediment thickness within southern Malawi, hence a range of values are used (Table A1). Uncertainty is highest in the Lower Shire Graben where no boreholes have penetrated basement , and where the contribution of Karoo rifting to hanging wall flexure of the Thyolo Fault also needs to be considered (Castaing, 1991;Chisenga et al, 2018). Castaing (1991) report throws of 1000 m for other Karoo faults in the Lower Shire Graben, and that the Thyolo Fault would have been in transtension during the main Permian to Lower Jurassic period of Karoo extension.…”

Section: Appendices Appendix A: Hanging-wall Flexure In Southern Malawimentioning

confidence: 99%

A systems-based approach to parameterise seismic hazard in regions with little historical or instrumental seismicity: The South Malawi Active Fault Database

Williams¹,

Mdala²,

Fagereng³

et al. 2020

Preprint

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Abstract. Seismic hazard is frequently characterised using instrumental seismic records. However, in regions where the instrumental record is short relative to earthquake repeat times, extrapolating it to estimate seismic hazard can misrepresent the probable location, magnitude, and frequency of future large earthquakes. Although paleoseismology can address this challenge, this approach requires certain geomorphic settings and carries large inherent uncertainties. Here, we outline how fault slip rates and recurrence intervals can be estimated through an approach that combines fault geometry, earthquake-scaling relationships, geodetically derived regional strain rates, and geological constraints of regional strain distribution. We then apply this approach to the southern Malawi Rift where, although no on-fault slip rate measurements exist, there are theoretical and observational constraints on how strain is distributed between border and intrabasinal faults. This has led to the development of the South Malawi Active Fault Database (SMAFD), the first database of its kind in the East African Rift System (EARS) and designed so that the outputs can be easily incorporated into Probabilistic Seismic Hazard Analysis. We estimate earthquake magnitudes of MW 5.4–7.2 for individual fault sections in the SMAFD, and MW 6.0–7.8 for whole fault ruptures. These potentially high magnitudes for continental normal faults reflect southern Malawi's 11–140 km long faults and thick (30–35 km) seismogenic crust. However, low slip rates (intermediate estimates 0.05–0.8 mm/yr) imply long recurrence intervals between events: 102–105 years for border faults and 103–106 years for intrabasinal faults. Sensitivity analysis indicates that the large range of these estimates can be reduced most significantly from an improved understanding of the rate and partitioning of rift-extension in southern Malawi, earthquake scaling relationships, and earthquake rupture scenarios. Hence these are critical areas for future research. The SMAFD provides a framework for using geological and geodetic information to characterize seismic hazard in low strain rate settings with few on-fault slip rate measurements, and could be adapted for use elsewhere in the EARS or globally.

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The structural re-interpretation of the Lower Shire Basin in the Southern Malawi rift using gravity data

Cited by 19 publications

References 28 publications

A systems-based approach to parameterise seismic hazard in regions with little historical or instrumental seismicity: active fault and seismogenic source databases for southern Malawi

A systems-based approach to parameterise seismic hazard in regions with little historical or instrumental seismicity: active fault and seismogenic source databases for southern Malawi

Structural inheritance and border fault reactivation during active early-stage rifting along the Thyolo fault, Malawi

A systems-based approach to parameterise seismic hazard in regions with little historical or instrumental seismicity: The South Malawi Active Fault Database

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