The Malawi Active Fault Database: an onshore-offshore database for regional assessment of seismic hazard and tectonic evolution

Williams, Jack N.; Wedmore, L. N. J.; Scholz, Christopher A.; Kolawole, Folarin; Wright, Lachlan J. M.; Shillington, D. J.; Fagereng, Åke; Biggs, Juliet; Mdala, Hassan; Dulanya, Zuze; Mphepo, Felix; Chindandali, P. R. N.; Werner, M. J.

doi:10.1002/essoar.10507158.1

Cited by 6 publications

(41 citation statements)

References 130 publications

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“…Malawi's national borders are closely aligned to a 900 km long section of the East African Rift's Western Branch, with earthquakes M W > 4.5 and active faults > 50 km long documented throughout (Fig. 1; Dixey, 1926;Ebinger, Rosendahl, & Reynolds, 1987;Specht & Rosendahl, 1989;Chapola & Kaphwiyo, 1992;Poggi et al, 2017;Williams, Wedmore, Scholz, et al, 2021a). In central and northern Malawi, the EAR has mostly been flooded by Lake Malawi, whilst in southern Malawi the rift is onshore and at its southern end has intersected and reactivated Karoo (i.e., Triassic-Jurassic) age faults in the Lower Shire Basin (Dulanya, 2017;Williams, Mdala, et al, 2021;Kolawole et al, 2021).…”

Section: Malawi 21 the Seismotectonic Setting Of Malawimentioning

confidence: 97%

“…Hazard levels were relatively uniform across Malawi in this study as it was part of a single ∼380,000 km 2 areal source zone that extends from Mozambique to southern Tanzania. However, geodetic models indicate that extension Williams, Wedmore, Scholz, et al, 2021a) and the Sub-Saharan Africa Global Earthquake Model (SSA-GEM) catalog (Poggi et al, 2017), and (b) regional geological terranes (Fullgraf et al, 2017). BMF; Bilila-Mtakataka Fault.…”

Section: Previous Seismic Hazard Assessment In Malawimentioning

confidence: 99%

“…Since 2015, high resolution digital elevation models (Hodge et al, 2019(Hodge et al, , 2020, aeromagnetic and gravity data (Kolawole et al, 2018(Kolawole et al, , 2021Chisenga et al, 2019), and a new generation of seismic reflection data in Lake Malawi (Shillington et al, 2016(Shillington et al, , 2020 have led to significant advances in the identification and mapping of active faults in Malawi. These datasets were combined into the Malawi Active Fault Database (MAFD), a geospatial database for 113 faults that are inferred to be active in Malawi and neighbouring areas of Mozambique and Tanzania (Williams, Wedmore, Scholz, et al, 2021a. In addition, new constraints on fault slip rates in Malawi have been provided from new geodetic data (Stamps et al, 2018;Wedmore et al, 2021) and the fault offsets of a 75 Ka.…”

Section: Previous Seismic Hazard Assessment In Malawimentioning

confidence: 99%

“…Deterministic seismic hazard assessment may therefore be an important tool for investigating seismic risk in Malawi. Furthermore, PSHA only considers ground motions, and so other possible secondary seismic hazards in Malawi, such as liquefaction, landslides and seiches (Williams, Wedmore, Scholz, et al, 2021a), are not considered here.…”

Section: Seismic Hazard and Risk In Malawimentioning

confidence: 99%

“…Malawi is located within a 900 km-long amagmatic section of the Western Branch of the East African Rift (EAR), and provides an ideal case study to investigate PSHA in a low strain rate region with a thick seismogenic layer as: (1) geodeticallyderived regional extension rates are low (0.5-2 mm/yr; Stamps et al, 2021;Wedmore et al, 2021), but nevertheless an order of magnitude higher than inferred from the last 50 years of instrumentally-recorded seismicity (Hodge et al, 2015;Ebinger et al, 2019), and (2) the seismogenic layer is ∼30-40 km thick (Jackson & Blenkinsop, 1993;Nyblade & Langston, 1995;Ebinger et al, 2019;Stevens et al, 2021;Craig & Jackson, 2021). Furthermore, constraints on the seismogenic potential of Malawi's active faults have improved with the collection of new geologic and geodetic data (Hodge et al, 2019;Shillington et al, 2020;Wedmore et al, 2021;Williams, Wedmore, Scholz, et al, 2021a;Kolawole et al, 2021), which have been synthesised for seismic hazard analysis in the Malawi Seismogenic Source Database (MSSD; Williams, Wedmore, Fagereng, et al, 2021a) .…”

Section: Introductionmentioning

confidence: 99%

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Fault-based Probabilistic Seismic Hazard Analysis in Regions with Low Strain Rates and a Thick Seismogenic Layer: A Case Study from Malawi

Williams

Werner

Goda

et al. 2022

Preprint

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In low strain rate regions, extrapolation of incomplete instrumental earthquake records is a limitation for probabilistic seismic hazard analysis (PSHA). This limitation can be addressed by incorporating geologic and geodetic data into fault-based seismogenic sources, although it is not always clear how on-fault magnitude-frequency distributions should be described and, if the seismogenic layer is especially thick, how these sources should be extrapolated down-dip. We explore these issues in the context of a new PSHA for Malawi, where regional extensional rates are 0.5-2 mm/yr, the seismogenic layer is 30-40 km thick, the instrumental catalog is ~60 years long, and fault-based sources were recently collated in the Malawi Seismogenic Source Database. Furthermore, Malawi is one of several countries along the East African Rift where exposure to seismic hazard is growing, but PSHA typically considers instrumental records alone. We use stochastic event catalogs to explore different fault-source down-dip extents and magnitude-frequency distributions. These indicate that hazard levels are highest for a Gutenberg-Richter on-fault magnitude-frequency distribution, even at low probabilities of exceedance (2% in 50 years), whilst seismic hazard levels are also sensitive to how relatively short (<50 km) fault sources are extrapolated down-dip. For sites close to fault sources (<40 km), seismic hazard levels are doubled compared to previous instrumental-seismicity based PSHA in Malawi. Cumulatively, these results highlight the need for careful fault source modelling in PSHA of low strain rate regions, and the need for new fault-based PSHA elsewhere in East Africa.

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Section: Malawi 21 the Seismotectonic Setting Of Malawimentioning

confidence: 97%

Section: Previous Seismic Hazard Assessment In Malawimentioning

confidence: 99%

Section: Previous Seismic Hazard Assessment In Malawimentioning

confidence: 99%

Section: Seismic Hazard and Risk In Malawimentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Fault-based Probabilistic Seismic Hazard Analysis in Regions with Low Strain Rates and a Thick Seismogenic Layer: A Case Study from Malawi

Williams

Werner

Goda

et al. 2022

Preprint

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Development of the Nyika Plateau, Malawi: A Long Lived Paleo‐Surface or a Contemporary Feature of the East African Rift?

McMillan

Boone

Kohn

et al. 2022

Geochem Geophys Geosyst

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Northern Malawi's Nyika Plateau is a 3,700 km2 large, highly elevated (∼2,500 m) plateau located at the western margin of the Miocene‐Recent Malawi rift and the confluence of multiple Proterozoic orogenic belts. Neighboring asthenospheric upwelling in the Rungwe Volcanic Province, associated with the active East African Rift, has created similar topographic highs, leading some to speculate that the formation of Nyika could be related. Here, we present new low‐temperature data using apatite fission track, apatite (U‐Th‐Sm)/He and zircon (U‐Th)/He thermochronology to constrain the upper crustal thermal history of the Nyika region since the Devonian. The data suggest that Nyika was an isolated feature since at least the Permo‐Triassic, well before more recent rifting in Malawi, and may have developed as a horst between two large Karoo grabens, the Henga‐Ruhuhu and the North Rukuru to the southeast and northwest, respectively. Similarities between the thermal histories of Nyika and the currently separated Livingstone Plateau to the east allow for the possibility that these may have been connected in a contiguous highland prior to the formation of the intervening Neogene Malawi rift. Thermal history models for exposed Precambrian basement samples adjacent to Nyika, and once buried beneath the neighboring Karoo basins, indicate that up to 3.4 km of Permo‐Triassic section has since been eroded, with samples along the plateau not indicating burial of Karoo‐type sediment at this time. Most recent cooling histories suggest that the plateau surface continued to denude at varying degrees from the Cretaceous and reached near‐surface temperatures in the Late Paleogene‐Neogene.

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Knickpoint morphotectonics of the Middle Shire River basin: Implications for the evolution of rift interaction zones

et al. 2022

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Tectonic and paleo‐environmental reconstructions of rift evolution typically rely on the interpretation of sedimentary sequences, but this is rarely possible in early‐stage rifts where sediment volumes are low. To overcome this challenge, we use geomorphology to investigate landscape evolution and the role of different forcing mechanisms during basin development. Here, we focus on the humid Middle Shire River basin, located within the zone of progressive interaction and linkage between the southern Malawi Rift and Shire Rift Zone, East Africa. We used a digital elevation model to map knickpoints and knickpoint morphologies in the Middle Shire River basin and examined the relationships with pre‐rift and syn‐rift structures within the rift interaction zone. The main axial stream, Shire River, descends steeply, 372 m over a 50 km distance, across exposed metamorphic basement along the rift floor, exhibiting a strongly disequilibrated longitudinal elevation profile with both ‘mobile’ and ‘fixed’ knickpoints. In particular, we identify two clusters of mobile knickpoints, which we interpret as associated with baselevel fall events at the downstream end of the exposed basement that triggered knickpoint migration through the fluvial network since at least the Mid. Pleistocene. We infer that after the integration of the axial stream across the Middle Shire Basin, the knickpoints migrate upstream in response to fault‐related subsidence in the Shire Rift Zone. Conversely, the fixed knickpoints are interpreted to reflect local differential bedrock erodibility at lithologic contacts or basement‐hosted fault scarps along the basin floor. The results suggest that Middle Shire basin opening, associated with rift linkage, is likely a recent event (at least Mid. Pleistocene) relative to the Late Oligocene activation of Cenozoic rifting in the East African Rift's Western Branch. These findings support the hypothesis that the Western Branch developed from the gradual propagation, linkage and coalescence of initially nucleated distinct rift basins.

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The Malawi Active Fault Database: an onshore-offshore database for regional assessment of seismic hazard and tectonic evolution

Abstract: Please refer to any applicable terms of use of the publisher.

Cited by 6 publications

References 130 publications

Fault-based Probabilistic Seismic Hazard Analysis in Regions with Low Strain Rates and a Thick Seismogenic Layer: A Case Study from Malawi

Fault-based Probabilistic Seismic Hazard Analysis in Regions with Low Strain Rates and a Thick Seismogenic Layer: A Case Study from Malawi

Development of the Nyika Plateau, Malawi: A Long Lived Paleo‐Surface or a Contemporary Feature of the East African Rift?

Knickpoint morphotectonics of the Middle Shire River basin: Implications for the evolution of rift interaction zones

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