the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 17 Jun 2022
The Luangwa Rift Active Fault Database and fault reactivation along the southwestern branch of the East African Rift
Luke N. J. Wedmore
Tess Turner
Juliet Biggs
Jack N. Williams
Henry M. Sichingabula
Christine Kabumbu
Kawawa Banda
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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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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- Final revised paper
Journal article(s) based on this preprint
Luke N. J. Wedmore et al.
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2022-304', Junjie Ren, 01 Jul 2022
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.
Citation: https://doi.org/10.5194/egusphere-2022-304-RC1 -
AC1: 'Reply on RC1', Luke Wedmore, 25 Aug 2022
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-304/egusphere-2022-304-AC1-supplement.pdf
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RC2: 'Comment on egusphere-2022-304', Tuo Wang, 18 Jul 2022
This manuscript systematically analyzed 18 identified active faults in the Luangwa Rift, using the SRTM data, and subsequently developed the Luangwa Rift Active Fault Database (LRAFD), which would provide valuable knowledge for future scientific study and implications on evaluating seismic hazard of the region. The authors adopted a previously proposed empirical relationship to estimate the magnitude (Mw) of the potential earthquakes and inferred the rift could host earthquakes up to Mw 8.1. Their resulting height measurements of the prominently exposed fault scarps (Chipola, Molaza, Chitumbi, and Kabungo) suggest that they were formed by multiple smaller events, rather than a single, large-magnitude one. In addition, the authors built a possible connection between the two border faults of the Luangwa Rift (Chipola and Molaza) and surface deformation. In general, I found the manuscript to be properly structured, and the contents of the manuscript are suitable for publication in the SE.
Specific comments:
Using an empirical relationship between the fault length and moment magnitude of earthquakes, the authors conclude that the fault could induce earthquakes up to Mw 8.1, a value that is greater than the historically recorded events in southern Africa. My concern is how confident are you with the resulting estimates, because it seems to me that there’s a certain degree of uncertainty here.
Technical corrections:
- Line 57: ‘Figure 1 & 2’ should be ‘Figures 1 & 2’, and same for the rest, i.e., lines 216, 224, 225, 228;
- Line 105: The abbreviation was ‘EARS’ (Line 54), not ‘EAR’, same for Line 248;
- Lines 112 - 113: The same sentence appears as the first sentence of the last paragraph;
- Lines 120 and 123: The audience would be benefited with the full names of GEM (Global Earthquake Model) and GIS (Geographic Information System);
- Lines 168 - 170: Please check the sentence;
- Lines 186 and 187: Dav or dav?
- Line 213: Do you mean Figure 5?
- Line 261: trees?
- Line 394: The abbreviation of ‘LRZ’ has not been indicated before.
Citation: https://doi.org/10.5194/egusphere-2022-304-RC2 -
AC2: 'Reply on RC2', Luke Wedmore, 25 Aug 2022
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-304/egusphere-2022-304-AC2-supplement.pdf
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RC3: 'Comment on egusphere-2022-304', Damien Delvaux, 26 Jul 2022
Comments on the preprint « The Luangwa Rift Active Fault Database and fault reactivation along the southwestern branch of the East African Rift” published by Wedmore et al.
I appreciate this work and the attempt to determine the quaternary fault architecture of the Luangwa Rift and to evaluate the potential seismic hazard.
You may consider also the work by Delvaux et al. (2012) on the segmentation and scarp height of the Kanda fault in the Rukwa rift.
- Delvaux, D., Kervyn, F., Macheyeki, A.S., Temu, E.B. (2012). Geodynamic significance of the TRM segment in the East African Rift (W-Tanzania): active tectonics and paleostress in the Ufipa plateau and Rukwa basin. Journal of Structural Geology, 37, 161-180. DOI: 10.1016/j.jsg.2012.01.008.
In this work, we stress the importance of field measurement of the scarp height. We found that the local fault morphology might influence the calculated scrap height. This means that the selection of the site for performing the fault scarp profile is important and difficult to perform on the basis of remote sensing only. The question is thus how did you selected the sites for extracting scarp profiles and how did you took into consideration the local geomorphology associated to the fault?
Citation: https://doi.org/10.5194/egusphere-2022-304-RC3 -
AC3: 'Reply on RC3', Luke Wedmore, 25 Aug 2022
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-304/egusphere-2022-304-AC3-supplement.pdf
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2022-304', Junjie Ren, 01 Jul 2022
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.
Citation: https://doi.org/10.5194/egusphere-2022-304-RC1 -
AC1: 'Reply on RC1', Luke Wedmore, 25 Aug 2022
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-304/egusphere-2022-304-AC1-supplement.pdf
-
RC2: 'Comment on egusphere-2022-304', Tuo Wang, 18 Jul 2022
This manuscript systematically analyzed 18 identified active faults in the Luangwa Rift, using the SRTM data, and subsequently developed the Luangwa Rift Active Fault Database (LRAFD), which would provide valuable knowledge for future scientific study and implications on evaluating seismic hazard of the region. The authors adopted a previously proposed empirical relationship to estimate the magnitude (Mw) of the potential earthquakes and inferred the rift could host earthquakes up to Mw 8.1. Their resulting height measurements of the prominently exposed fault scarps (Chipola, Molaza, Chitumbi, and Kabungo) suggest that they were formed by multiple smaller events, rather than a single, large-magnitude one. In addition, the authors built a possible connection between the two border faults of the Luangwa Rift (Chipola and Molaza) and surface deformation. In general, I found the manuscript to be properly structured, and the contents of the manuscript are suitable for publication in the SE.
Specific comments:
Using an empirical relationship between the fault length and moment magnitude of earthquakes, the authors conclude that the fault could induce earthquakes up to Mw 8.1, a value that is greater than the historically recorded events in southern Africa. My concern is how confident are you with the resulting estimates, because it seems to me that there’s a certain degree of uncertainty here.
Technical corrections:
- Line 57: ‘Figure 1 & 2’ should be ‘Figures 1 & 2’, and same for the rest, i.e., lines 216, 224, 225, 228;
- Line 105: The abbreviation was ‘EARS’ (Line 54), not ‘EAR’, same for Line 248;
- Lines 112 - 113: The same sentence appears as the first sentence of the last paragraph;
- Lines 120 and 123: The audience would be benefited with the full names of GEM (Global Earthquake Model) and GIS (Geographic Information System);
- Lines 168 - 170: Please check the sentence;
- Lines 186 and 187: Dav or dav?
- Line 213: Do you mean Figure 5?
- Line 261: trees?
- Line 394: The abbreviation of ‘LRZ’ has not been indicated before.
Citation: https://doi.org/10.5194/egusphere-2022-304-RC2 -
AC2: 'Reply on RC2', Luke Wedmore, 25 Aug 2022
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-304/egusphere-2022-304-AC2-supplement.pdf
-
RC3: 'Comment on egusphere-2022-304', Damien Delvaux, 26 Jul 2022
Comments on the preprint « The Luangwa Rift Active Fault Database and fault reactivation along the southwestern branch of the East African Rift” published by Wedmore et al.
I appreciate this work and the attempt to determine the quaternary fault architecture of the Luangwa Rift and to evaluate the potential seismic hazard.
You may consider also the work by Delvaux et al. (2012) on the segmentation and scarp height of the Kanda fault in the Rukwa rift.
- Delvaux, D., Kervyn, F., Macheyeki, A.S., Temu, E.B. (2012). Geodynamic significance of the TRM segment in the East African Rift (W-Tanzania): active tectonics and paleostress in the Ufipa plateau and Rukwa basin. Journal of Structural Geology, 37, 161-180. DOI: 10.1016/j.jsg.2012.01.008.
In this work, we stress the importance of field measurement of the scarp height. We found that the local fault morphology might influence the calculated scrap height. This means that the selection of the site for performing the fault scarp profile is important and difficult to perform on the basis of remote sensing only. The question is thus how did you selected the sites for extracting scarp profiles and how did you took into consideration the local geomorphology associated to the fault?
Citation: https://doi.org/10.5194/egusphere-2022-304-RC3 -
AC3: 'Reply on RC3', Luke Wedmore, 25 Aug 2022
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-304/egusphere-2022-304-AC3-supplement.pdf
Peer review completion
Journal article(s) based on this preprint
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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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(11159 KB) - Metadata XML
-
Supplement
(303 KB) - BibTeX
- EndNote
- Final revised paper