16 Nov 2021
16 Nov 2021
Status: a revised version of this preprint is currently under review for the journal NHESS.

Geologic and geodetic constraints on the seismic hazard of Malawi’s active faults: The Malawi Seismogenic Source Database (MSSD)

Jack N. Williams1,2,a, Luke N. J. Wedmore2, Åke Fagereng1, Maximilian J. Werner2, Hassan Mdala3, Donna J. Shillington4, Christopher A. Scholz5, Folarin Kolawole6, Lachlan J. M. Wright5, Juliet Biggs2, Zuze Dulanya7, Felix Mphepo3, and Patrick Chindandali8 Jack N. Williams et al.
  • 1School of Environmental Sciences, Cardiff University, Cardiff, UK
  • 2School of Earth Sciences, University of Bristol, Bristol, UK
  • 3Geological Survey Department, Mzuzu Regional Office, Mzuzu, Malawi
  • 4School of Earth and Sustainability, Northern Arizona University, Flagstaff, Arizona, USA
  • 5Department of Earth Sciences, Syracuse University, Syracuse, New York, USA
  • 6BP America, Houston, Texas, U.S.
  • 7Geography and Earth Sciences Department, University of Malawi, Zomba, Malawi
  • 8Geological Survey Department, Zomba, Malawi
  • anow at: the Department of Geology, University of Otago, Dunedin, New Zealand

Abstract. 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.

Jack N. Williams et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on nhess-2021-306', Anonymous Referee #1, 16 Dec 2021
    • AC1: 'Reply on RC1', Jack Williams, 05 Apr 2022
  • RC2: 'Comment on nhess-2021-306', Luigi Ferranti, 19 Feb 2022
    • AC2: 'Reply on RC2', Jack Williams, 05 Apr 2022

Jack N. Williams et al.

Data sets

Malawi Seismogenic Source Database Williams, Jack N.; Wedmore, Luke N. J.; Fagereng, Åke; Werner, Maximilian J.; Biggs, Juliet; Mdala, Hassan; Kolawole, Folarin; Shillington, Donna J.; Dulanya, Zuze; Mphepo, Felix; Chindandali, Patrick R. N.; Wright, Lachlan J. M.; Scholz, Christopher A.

Malawi Active Faut Database Williams, Jack; Wedmore, Luke; Scholz, Christopher A; Kolawole, Folarin; Wright, Lachlan J M; Shillington, Donna J; Fagereng, Å; Biggs, Juliet; Mdala, Hassan; Dulanya, Zuze; Mphepo, Felix; Chindandali, Patrick; Werner, Maximilian J

Jack N. Williams et al.


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Short summary
We use geologic and GPS data to constrain the magnitude and frequency of earthquakes that occur along active faults in Malawi. These faults slip in earthquakes as the tectonic plates either side of the East African Rift in Malawi diverge from one another. Low divergence rates (0.5–1.5 mm/yr) and long faults (5–200 km) imply that earthquakes along these faults are rare (once every 1,000–10,000 years) but could have high magnitudes (M 7–8). These data can be used to assess seismic risk in Malawi.