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

Wedmore, L. N. J.; Williams, Jack N.; Biggs, Juliet; Fagereng, Åke; Mphepo, Felix; Dulanya, Zuze; Willoughby, James; Mdala, Hassan; Adams, B. A.

doi:10.1016/j.jsg.2020.104097

Cited by 31 publications

(53 citation statements)

References 144 publications

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“…We find that although generally comparable for M W < 7.5, the Wells and Coppersmith (1994) regression overestimates magnitudes relative to Leonard (2010) (Fig. 5d).…”

Section: Earthquake Magnitudes and Recurrence Intervalsmentioning

confidence: 49%

“…A is the fault area calculated from L fault and W using Eq. (1), WC94 is from Wells and Coppersmith (1994), and W08 is from Wesnousky (2008).…”

Section: Estimating Fault Slip Ratesmentioning

confidence: 99%

“…Scaling relationships between fault length and average single-event displacement (D) can then be combined with slip rate estimates to calculate earthquake recurrence intervals (R) through the relationship R = D / slip rate (Wallace, 1970). To select an appropriate set of earthquake-scaling relationships for the SMSSD, we consider three previously reported regressions and apply them to its mapped faults: (1) between normal fault length and M W (Wesnousky, 2008), (2) interplate dipslip fault length and M W (Leonard, 2010), and (3) fault area and M W (Wells and Coppersmith, 1994) where A is calculated using W derived from Eq. (1).…”

Section: Earthquake Magnitudes and Recurrence Intervalsmentioning

confidence: 99%

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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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“…We find that although generally comparable for M W < 7.5, the Wells and Coppersmith (1994) regression overestimates magnitudes relative to Leonard (2010) (Fig. 5d).…”

Section: Earthquake Magnitudes and Recurrence Intervalsmentioning

confidence: 49%

“…A is the fault area calculated from L fault and W using Eq. (1), WC94 is from Wells and Coppersmith (1994), and W08 is from Wesnousky (2008).…”

Section: Estimating Fault Slip Ratesmentioning

confidence: 99%

Section: Earthquake Magnitudes and Recurrence Intervalsmentioning

confidence: 99%

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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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“…One style (Style-1 strain localization) is the localization of a large rift fault onto a narrow discrete zone of basement weakness, such as prominent basement terrane boundaries (this study), pre-existing fault zones, and narrow ductile shear zones, in which case the structures of the weak zone and the fabrics of the adjacent basement may influence the fault geometry (Figure 6). An example of this is the development of the Livingstone Fault in the Karonga Basin, northern Malawi Rift (Wheeler and Karson, 1989), the Thyolo border fault in the Shire Rift Zone (Wedmore et al, 2020b), and splay faulting at a terrane boundary during the Late Cretaceous extension between Zealandia and Australia (Phillips and McCaffrey, 2019b). A second style (Style-2 strain localization) is the localization of a fault cluster (or fault belt) onto a broader discrete zone of basement weakness, such as wide pre-rift shear zones or subduction suture zones (this study), in which case the individual fault strands may exploit the smaller-scale mechanical heterogeneities within the broad zone of basement weakness (Figure 6).…”

Section: Implications For Early-stage Architecture Of Continental Rift Basinsmentioning

confidence: 99%

Structural Inheritance Controls Strain Distribution During Early Continental Rifting, Rukwa Rift

Kolawole¹,

Phillips²,

Atekwana³

et al. 2021

Front. Earth Sci.

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Little is known about rift kinematics and strain distribution during the earliest phase of extension due to the deep burial of the pre-rift and earliest rift structures beneath younger, rift-related deposits. Yet, this exact phase of basin development ultimately sets the stage for the location of continental plate divergence and breakup. Here, we investigate the structure and strain distribution in the multiphase Late Paleozoic-Cenozoic magma-poor Rukwa Rift, East Africa during the earliest phase of extension. We utilize aeromagnetic data that image the Precambrian Chisi Shear Zone (CSZ) and bounding terranes, and interpretations of 2-D seismic reflection data to show that, during the earliest rift phase (Permo-Triassic ‘Karoo’): 1) the rift was defined by the Lupa border fault, which exploited colinear basement terrane boundaries, and a prominent intra-basinal fault cluster (329° ± 9.6) that trends parallel to and whose location was controlled by the CSZ (326°); 2) extensional strain in the NW section of the rift was accommodated by both the intra-basinal fault cluster and the border fault, where the intra-basinal faulting account for up to 64% of extension; in the SE where the CSZ is absent, strain is primarily focused on the Lupa Fault. Here, the early-rift strain is thus, not accommodated only by border the fault as suggested by existing magma-poor early-rift models; instead, strain focuses relatively quickly on a large border fault and intra-basinal fault clusters that follow pre-existing intra-basement structures; 3) two styles of early-rift strain localization are evident, in which strain is localized onto a narrow discrete zone of basement weakness in the form of a large rift fault (Style-1 localization), and onto a broader discrete zone of basement weakness in the form of a fault cluster (Style-2 localization). We argue that the CSZ and adjacent terrane boundaries represent zones of mechanical weakness that controlled the first-order strain distribution and rift development during the earliest phase of extension. The established early-rift structure, modulated by structural inheritance, then persisted through the subsequent rift phases. The results of our study, in a juvenile and relatively well-exposed and data-rich rift, are applicable to understanding the structural evolution of deeper, buried ancient rifts.

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“…: Crider, 2015 ; Crider & Peacock, 2004 ; d'Alessio & Martel, 2005 ; Davatzes & Aydin, 2003 ; Fondriest et al., 2020 , 2012 ; Mandl, 1988 ; Martel, 1990 ; Mittempergher et al., 2021 ; Nasseri et al., 2003 , 1997 ; Pachell & Evans, 2002 ; Peacock & Sanderson, 1995 ; Pennacchioni et al., 2006 ; Segall & Pollard, 1983 ; Sibson, 1990 ; Smith et al., 2013 ; Swanson, 1988 , 2006b ; Sylvester, 1988 ). Geologic and geophysical studies, rock analog experiments, and numerical models have highlighted that crustal‐scale (i.e., tens of km‐long) brittle faults commonly exploit exhumed mylonitic horizons in the crystalline basement (e.g., Balázs et al., 2018 ; Bellahsen & Daniel, 2005 ; Bistacchi et al., 2010 , 2012 ; Butler et al., 2008 ; Collanega et al., 2019 ; Hodge et al., 2018 ; Holdsworth et al., 2011 ; Massironi et al., 2011 ; Naliboff et al., 2020 ; Phillips et al., 2019 ; Stewart et al., 2000 ; Storti et al., 2003 ; Sylvester, 1988 ; Wedmore et al., 2020 ; Whipp et al., 2014 ). Nevertheless, only a few contributions have attempted to evaluate the influence of precursory structures over crustal‐scale faults (e.g., Bistacchi et al., 2010 ; Hodge et al., 2018 ; Wedmore et al., 2020 ).…”

Section: Introductionmentioning

confidence: 99%

Structural Evolution of a Crustal‐Scale Seismogenic Fault in a Magmatic Arc: The Bolfin Fault Zone (Atacama Fault System)

et al. 2021

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How major crustal‐scale seismogenic faults nucleate and evolve in crystalline basements represents a long‐standing, but poorly understood, issue in structural geology and fault mechanics. Here, we address the spatio‐temporal evolution of the Bolfin Fault Zone (BFZ), a >40‐km‐long exhumed seismogenic splay fault of the 1000‐km‐long strike‐slip Atacama Fault System. The BFZ has a sinuous fault trace across the Mesozoic magmatic arc of the Coastal Cordillera (Northern Chile) and formed during the oblique subduction of the Aluk plate beneath the South American plate. Seismic faulting occurred at 5–7 km depth and ≤ 300°C in a fluid‐rich environment as recorded by extensive propylitic alteration and epidote‐chlorite veining. Ancient (125–118 Ma) seismicity is attested by the widespread occurrence of pseudotachylytes. Field geologic surveys indicate nucleation of the BFZ on precursory geometrical anisotropies represented by magmatic foliation of plutons (northern and central segments) and andesitic dyke swarms (southern segment) within the heterogeneous crystalline basement. Seismic faulting exploited the segments of precursory anisotropies that were optimal to favorably oriented with respect to the long‐term far‐stress field associated with the oblique ancient subduction. The large‐scale sinuous geometry of the BFZ resulted from the hard linkage of these anisotropy‐pinned segments during fault growth.

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

Cited by 31 publications

References 144 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 Controls Strain Distribution During Early Continental Rifting, Rukwa Rift

Structural Evolution of a Crustal‐Scale Seismogenic Fault in a Magmatic Arc: The Bolfin Fault Zone (Atacama Fault System)

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