The Luangwa Rift Active Fault Database and fault reactivation along the southwestern branch of the East African Rift
- 1School of Earth Sciences, University of Bristol, Bristol, UK
- 2School of Earth and Environmental Sciences, Cardiff University, Cardiff, UK
- 3Department of Geology, University of Otago, Dunedin, New Zealand
- 4Department of Geography and Environmental Studies, University of Zambia, Lusaka, Zambia
- 5Department of Geology, School of Mines, University of Zambia, Lusaka, Zambia
- 1School of Earth Sciences, University of Bristol, Bristol, UK
- 2School of Earth and Environmental Sciences, Cardiff University, Cardiff, UK
- 3Department of Geology, University of Otago, Dunedin, New Zealand
- 4Department of Geography and Environmental Studies, University of Zambia, Lusaka, Zambia
- 5Department of Geology, School of Mines, University of Zambia, Lusaka, Zambia
Abstract. Seismic hazard assessment in slow straining regions is challenging because earthquake catalogues only record events from approximately the last 100 years, whereas earthquake recurrence times on individual faults can exceed 1,000 years. Systematic mapping of active faults allows fault sources to be used within probabilistic seismic hazard assessment, which overcomes the problems of short-term earthquake records. We use Shuttle Radar Topography Mission (SRTM) data to analyse surface deformation in the Luangwa Rift in Zambia and develop the Luangwa Rift Active Fault Database (LRAFD). The LRAFD is an open-source geospatial database containing active fault traces and their attributes and is freely available at: https://doi.org/10.5281/zenodo.6513691. We identified 18 faults that display evidence for Quaternary activity and empirical relationships suggest that these faults could cause earthquakes up to Mw 8.1, which would exceed the magnitude of historically recorded events in southern Africa. On the four most prominent faults, the median height of Late Quaternary fault scarps varies between 12.9 ± 0.4 and 19.2 ± 0.9 m, which suggests they were formed by multiple earthquakes. Deformation is focused on the edges of the Luangwa Rift: the most prominent Late Quaternary fault scarps occur along the 207 km long Chipola and 142 km long Molaza faults, which are the rift border faults and the longest faults in the region. We associate the scarp on the Molaza Fault with possible surface ruptures from two 20th Century earthquakes. Thus, the LRAFD reveals new insights into active faulting in southern Africa and presents a framework for evaluating future seismic hazard.
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Luke N. J. Wedmore et al.
Status: open (until 30 Jul 2022)
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RC1: 'Comment on egusphere-2022-304', Junjie Ren, 01 Jul 2022
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This study uses SRTM data to analyze surface deformation along the Luangwa rift and develops a database for active faults in the Luangwa rift. The author proposed 18 potentially active faults and estimated the possible magnitudes up to Mw 8.1 for these faults. They also estimate the scarp heights based on the STRM data and use the empirical relationship between magnitude and fault length to assess the maximum earthquake. These data can provide insights into active tectonics and associated seismic hazards in southern Africa.
There are some comments on this manuscript.
- An active fault has been widely defined via offset late Quaternary landforms or sediments. In this study, no field observation on these faults can show any evidence for the latest activities. For large earthquakes, we can often find coseismic surface ruptures. There is a historic earthquake in the 20th Some records in the history may help you.
- You suggest the fault scarps on the alluvial fan. Do you have any evidence for the fan age and the same geomorphic units on the both sides of the fault?
- The magnitudes are estimated via the empirical relationship of magnitude and fault length. The results include many uncertainties. Maybe a large earthquake can rupture several branches. Also, the earthquakes on a fault have a similar depth. Only using the fault length to estimate the depth is not suitable.
- No age, no rates. So your slip rates and associate recurrence intervals are not reliable. Your database of active faults is very nice. Maybe your analysis is over-interpret
- In L274, The minimum heights using the SRTM data are 2-3 m, but your results show a high resolution like 0.08 m or 0.2 m. It is impossible.
- L169-170: this sentence is not clear. Please check it.
- Line274: was—are
- Line 286: add m.
- Figure 4 show a nearly N-S-striking linear feature between faults 11 and 15 on the west side of the rift.
- Please show the profile locations of figure 9 in the other figure.
Luke N. J. Wedmore et al.
Data sets
Luangwa Rift Fault Scarp Measurements Turner, T., Wedmore, L. N. J., Biggs, J. https://doi.org/10.5281/zenodo.6513545
Luangwa Rift Active Fault Database Wedmore, L. N. J., Turner, T., Biggs, J., Williams, J. N., Sichingabula, H., Kabumbu, C., Banda, K. https://doi.org/10.5281/zenodo.6513691
Luangwa Rift Seismogenic Source Properties Turner, T., Wedmore, L. N. J., Biggs, J., Williams, J. N., Sichingabula, H., Kabumbu, C., Banda, K. https://doi.org/10.5281/zenodo.6513778
Luke N. J. Wedmore et al.
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