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Geologic and geodetic constraints on the magnitude and frequency of earthquakes along Malawi’s active faults: the Malawi seismogenic source model (MSSM)

Williams, Jack ORCID:, Wedmore, Luke N.J., Fagereng, Ake ORCID:, Werner, M.J., Mdala, Hassan, Shillington, Donna J., Scholz, Christopher A., Kolawole, Folarin, Wright, Lachlan J.M., Biggs, Juliet, Dulanye, Zuze, Mphepo, Felix and Chindandali, Patrick 2022. Geologic and geodetic constraints on the magnitude and frequency of earthquakes along Malawi’s active faults: the Malawi seismogenic source model (MSSM). Natural Hazards and Earth System Sciences 22 (11) , pp. 3607-3639. 10.5194/nhess-22-3607-2022

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Active fault data are commonly used in seismic hazard assessments, but there are challenges in deriving the slip rate, geometry, and frequency of earthquakes along active faults. Herein, we present the open-access geospatial Malawi Seismogenic Source Database (MSSD), which describes the seismogenic properties of faults that have formed during East African rifting in Malawi. We first use empirical observations to geometrically classify active faults into section, fault, and multi-fault seismogenic sources. For sources in the North Basin of Lake Malawi, slip rates can be derived from the vertical offset of a seismic reflector that is estimated to be 75 ka based on dated core. Elsewhere, slip rates are constrained from advancing a ‘systems-based’ approach that partitions geodetically-derived rift extension rates in Malawi between seismogenic sources using a priori constraints on regional strain distribution in magma-poor continental rifts. Slip rates are then combined with source geometry and empirical scaling relationships to estimate earthquake magnitudes and recurrence intervals, and their uncertainty is described from the variability of outcomes from a logic tree used in these calculations. We find that for sources in the Lake Malawi’s North Basin, where slip rates can be derived from both the geodetic data and the offset seismic reflector, the slip rate estimates are within error of each other, although those from the offset reflector are higher. Sources in the MSSD are 5–200 km long, which implies that large magnitude (MW 7–8) earthquakes may occur in Malawi. Low slip rates (0.05–2 mm/yr), however, mean that the frequency of such events will be low (recurrence intervals ~103–104 years). The MSSD represents an important resource for investigating Malawi’s increasing seismic risks and provides a framework for incorporating active fault data into seismic hazard assessment in other tectonically active regions.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Environmental Sciences
Publisher: European Geosciences Union
ISSN: 1684-9981
Date of First Compliant Deposit: 2 November 2022
Date of Acceptance: 11 October 2022
Last Modified: 18 May 2023 16:50

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