The drivers of Lower Crustal Earthquakes Along Magma-poor Portions of the East African Rift
Main Article Content
Abstract
Deep earthquakes along magma-poor sections of the East African Rift System (EARS) challenge our understanding of the controls on seismogenic thickness because they occur at greater depths and higher temperatures than the frictional-viscous transition zone in typical continental crust. Using a recently published catalogue of relocated earthquakes in southeastern Africa, we demonstrate that seismicity occurs down to the ~40 km deep Moho throughout the magma-poor southern EARS. We then explore the mechanisms that can account for this deep seismicity by combining 1D lithospheric strength profiles with available regional measurements of Moho thickness, the ratio of the crust's P- and S-wave velocities (VP/VS), and heat flow. As suggested by previous studies, we find that a mafic lower crustal composition, lower geothermal gradient, and/or high pore fluid pressure can locally facilitate the observed deep seismicity. However, there are sections of the southern EARS where the lower crust is felsic, dry, and warm, and in these cases, we propose that the embrittlement of the lower crust is best explained by strain localisation in space and time. This strain localisation could occur because fault and shear zones in magma-poor sections of the EARS are unusually narrow, or because strain is localised in space and time following large magnitude earthquakes.
Article Details
References
Afonso, J. C., and G. Ranalli (2004), Crustal and mantle strengths in continental lithosphere: is the jelly sandwich model obsolete?, Tectonophysics, 394(3-4), 221–232, doi: 10.1016/j.tecto.2004.08.006.
Ajala, R., F. Kolawole, and W. Menke (2024), Blind magmatism abets nonvolcanic continental rifting, Communications earth & environment, 5(1), 1–8, doi: 10.1038/s43247-024-01244-7.
Albaric, J., J. Déverchère, J. Perrot, A. Jakovlev, and Deschamps (2014), Deep crustal earthquakes in North Tanzania, East Africa: Interplay between tectonic and magmatic processes in an incipient rift, Geochemistry, geophysics, geosystems: G(3), 15(2), 374–394, doi: 10.1002/2013gc005027.
Ambraseys, N. N., and R. D. Adams (1992), Reappraisal of major African earthquakes, south of 20°N, 1900–1930, Tectonophysics, 209(1-4), 293–296, doi: 10.1016/0040-1951(92)90036-6.
Ben-Zion, Y., and V. Lyakhovsky (2006), Analysis of aftershocks in a lithospheric model with seismogenic zone governed by damage rheology, Geophysical journal international, 165(1), 197–210, doi: 10.1111/j.1365-246x.2006.02878.x.
Biggs, J., E. Nissen, T. Craig, J. Jackson, and D. P. Robinson (2010), Breaking up the hanging wall of a rift-border fault: The 2009 Karonga earthquakes, Malawi: THE 2009 KARONGA EARTHQUAKES, MALAWI, Geophysical research letters, 37 (11), doi: 10.1029/2010gl043179.
Biggs, J., A. Ayele, T. P. Fischer, K. Fontijn, W. Hutchison, E. Kazimoto, K. Whaler, and T. J. Wright (2021), Volcanic activity and hazard in the East African Rift Zone, Nature communications, 12(1), 6881, doi: 10.1038/s41467-021-27166-y.
Birhanu, Y., R. Bendick, S. Fisseha, E. Lewi, M. Floyd, R. King, and R. Reilinger (2016), GPS constraints on broad scale extension in the Ethiopian Highlands and Main Ethiopian Rift, Geophysical research letters, 43(13), 6844–6851, doi: 10.1002/2016gl069890.
Borrego, D., A. A. Nyblade, N. J. Accardo, J. B. Gaherty, C. J. Ebinger, D. J. Shillington, P. R. N. Chindandali, G. Mbogoni, R. W. Ferdinand, G. Mulibo, J. P. O’Donnell, M. Kachingwe, and G. Tepp (2018), Crustal structure surrounding the northern Malawi rift and beneath the Rungwe Volcanic Province, East Africa, Geophysical journal international, 215(2), 1410–1426, doi: 10.1093/gji/ggy331.
Brace, W. F. (1972), Laboratory studies of stick-slip and their application to earthquakes, Tectonophysics, 14(3-4), 189–200, doi: 10.1016/0040-1951(72)90068-6.
Buck, W. R. (2004), Consequences of asthenospheric variability on continental rifting, in Rheology and Deformation of the Lithosphere at Continental Margins, edited by G. D. Karner, B. Taylor, N. W. Driscoll, and D. L. Kohlstedt, pp. 1–30, Columbia University Press, New York Chichester, West Sussex, doi: 10.7312/karn12738-002.
Campbell, L. R., L. Menegon, A. Fagereng, and G. Pennacchioni (2020), Earthquake nucleation in the lower crust by local stress amplification, Nature communications, 11(1), 1322, doi: 10.1038/s41467-020-15150-x.
Carpenter, M., J. N. Williams, A. Fagereng, L. N. J. Wedmore, J. Biggs, F. Mphepo, H. Mdala, Z. Dulanya, and B. Manda (2022), Comparing intrarift and border fault structure in the Malawi Rift: Implications for normal fault growth, Journal of structural geology, 165(104761), 104,761, doi: 10.1016/j.jsg.2022.104761.
Christensen, N. I. (1996), Poisson’s ratio and crustal seismology, Journal of geophysical research. Solid earth, 101(2), 3139–3156, doi: 10.1029/95JB03446.
Copley, A., J. Hollingsworth, and E. Bergman (2012), Constraints on fault and lithosphere rheology from the coseismic slip and postseismic afterslip of the 2006 Mw7.0 Mozambique earthquake: MOZAMBIQUE EARTHQUAKE AND AFTERSLIP, Journal of geophysical research, 117 (B3), doi: 10.1029/2011jb008580.
Craig, T. J., and J. A. Jackson (2021), Variations in the seismogenic thickness of east Africa, Journal of geophysical research. Solid earth, 126(3), 1–15, doi: 10.1029/2020jb020754.
Craig, T. J., J. A. Jackson, K. Priestley, and D. Mckenzie (2011), Earthquake distribution patterns in Africa: Their relationship to variations in lithospheric and geological structure, and their rheological implications, Geophysical journal international, 185(1), 403–434, doi: 10.1111/j.1365-246X.2011.04950.x.
Daly, M. C., P. Green, A. B. Watts, O. Davies, F. Chibesakunda, and R. Walker (2020), Tectonics and landscape of the central African plateau and their implications for a propagating southwestern rift in Africa, Geochemistry, geophysics, geosystems: G(3), 21(6), doi: 10.1029/2019gc008746.
Degens, E. T., R. P. Von Herzen, and H.-K. Wong (1971), Lake tanganyika: Water chemistry, sediments, geological structure, The Science of Nature, 58(5), 229–241, doi: 10.1007/bf00602986.
Delvaux, D., J.-L. Mulumba, M. N. S. Sebagenzi, S. F. Bondo, F. Kervyn, and H.-B. Havenith (2017), Seismic hazard assessment of the Kivu rift segment based on a new seismotectonic zonation model (western branch, East African Rift system), Journal of African earth sciences (Oxford, England: 1994), 134, 831–855, doi: 10.1016/j.jafrearsci.2016.10.004.
Dávalos-Elizondo, E., E. A. Atekwana, E. A. Atekwana, G. Tsokonombwe, and D. A. Laó-Dávila (2021), Medium to low enthalpy geothermal reservoirs estimated from geothermometry and mixing models of hot springs along the Malawi Rift Zone, Geothermics, 89(101963), 101,963, doi: 10.1016/j.geothermics.2020.101963.
Déverchère, J., C. Petit, N. Gileva, N. Radziminovitch, V. Melnikova, and V. San’Kov (2001), Depth distribution of earthquakes in the Baikal rift system and its implications for the rheology of the lithosphere, Geophysical journal international, 146(3), 714–730, doi: 10.1046/j.0956-540x.2001.1484.484.x.
Ebinger, C. J. (1989), Tectonic development of the western branch of the East African rift system, Geological Society of America bulletin, 101(7), 885–903, doi: 10.1130/0016-7606(1989)101<0885:TDOTWB>2.3.CO;2.
Ebinger, C. J., B. R. Rosendahl, and D. J. Reynolds (1987), Tectonic model of the Malaŵi rift, Africa, Tectonophysics, 141(1-3), 215–235, doi: 10.1016/0040-1951(87)90187-9.
Ebinger, C. J., S. J. Oliva, T.-Q. Pham, K. Peterson, P. Chindandali, F. Illsley-Kemp, C. Drooff, D. J. Shillington, N. J. Accardo, R. J. Gallacher, J. Gaherty, A. A. Nyblade, and G. Mulibo (2019), Kinematics of active deformation in the Malawi rift and Rungwe Volcanic Province, Africa, Geochemistry, geophysics, geosystems: G(3), 20(8), 3928–3951, doi: 10.1029/2019gc008354.
Fagereng, A. (2013), Fault segmentation, deep rift earthquakes and crustal rheology: Insights from the 2009 Karonga sequence and seismicity in the Rukwa–Malawi rift zone, Tectonophysics, 601, 216–225, doi: 10.1016/j.tecto.2013.05.012.
Fagereng, A., J. F. A. Diener, C. J. Tulley, and Manda (2024), Metamorphic inheritance, lower-crustal earthquakes, and continental rifting, Geochemistry, geophysics, geosystems: G(3), 25(3), doi: 10.1029/2023gc011305.
Fonseca, J. F. B. D., J. Chamussa, A. Domingues, G. Helffrich, E. Antunes, G. van Aswegen, L. V. Pinto, S. Custodio, and V. J. Manhica (2014), MOZART: A seismological investigation of the east African rift in central Mozambique, Seismological research letters, 85(1), 108–116, doi: 10.1785/0220130082.
Foster, A. N., and J. A. Jackson (1998), Source parameters of large African earthquakes:implications for crustal rheology and regional kinematics: Source parameters of large African earthquakes, Geophysical journal international, 134(2), 422–448, doi: 10.1046/j.1365-246x.1998.00568.x.
Fuchs, S., G. Beardsmore, P. Chiozzi, O. M. Espinoza-Ojeda, G. Gola, W. Gosnold, R. Harris, S. Jennings, S. Liu, R. Negrete-Aranda, F. Neumann, B. Norden, J. Poort, D. Rajver, L. Ray, M. Richards, J. D. Smith, A. Tanaka, and M. Verdoya (2021a), A new database structure for the IHFC Global Heat Flow Database, International Journal of Terrestrial Heat Flow and Applications, 4(1), 1–14, doi: 10.31214/ijthfa.v4i1.62.
Fuchs, S., B. Norden, and International Heat Flow Commission (2021b), The Global Heat Flow Database: Release 2021, doi: 10.5880/FIDGEO.2021.014.
Gaherty, J. B., W. Zheng, D. J. Shillington, M. E. Pritchard, S. T. Henderson, P. R. N. Chindandali, H. Mdala, A. Shuler, N. Lindsey, S. J. Oliva, S. Nooner, C. A. Scholz, D. Schaff, G. Ekström, and M. Nettles (2019), Faulting processes during early-stage rifting: seismic and geodetic analysis of the 2009–2010 Northern Malawi earthquake sequence, Geophysical journal international, 217 (3), 1767–1782, doi: 10.1093/gji/ggz119.
Gardonio, B., R. Jolivet, E. Calais, and H. Leclère (2018), The April 2017 Mw 6.5 Botswana earthquake: An intraplate event triggered by deep fluids, Geophysical research letters, 45(17), 8886–8896, doi: 10.1029/2018gl078297.
Gounon, A., J. Letort, F. Cotton, G. Weatherill, M. Sylvander, and S. Latour (2021), Improving depth estimations of African earthquakes using teleseismic data, and influence for the East-African rift seismic hazard characterization, Geophysical journal international, 228(1), 447–460, doi: 10.1093/gji/ggab348.
Grant, C., F. Kolawole, and J. Williams (2024), Evolution of rift faulting in incipient, magma-poor divergent plate boundaries: New insights from the Okavango-Makgadikgadi Rift Zone, Botswana, Earth and planetary science letters, 646(118957), 118,957, doi: 10.1016/j.epsl.2024.118957.
Hamiel, Y., G. Baer, L. Kalindekafe, K. Dombola, and P. Chindandali (2012), Seismic and aseismic slip evolution and deformation associated with the 2009-2010 northern Malawi earthquake swarm, East African Rift: The 2009-2010 northern Malawi earthquake swarm, Geophysical journal international, 191(3), no–no, doi: 10.1111/j.1365-246x.2012.05673.x.
Hellebrekers, N., A. R. Niemeijer, A. Fagereng, B. Manda, and R. L. S. Mvula (2019), Lower crustal earthquakes in the East African Rift System: Insights from frictional properties of rock samples from the Malawi rift, Tectonophysics, 767 (228167), 228,167, doi: 10.1016/j.tecto.2019.228167.
Hirth, G., and N. M. Beeler (2015), The role of fluid pressure on frictional behavior at the base of the seismogenic zone, Geology, 43(3), 223–226, doi: 10.1130/G36361.1.
Hirth, G., and D. L. Kohlstedt (2003), Rheology of the upper mantle and the mantle wedge: A view from the experimentalists BT - geophysical monograph series, Geophysical Monograph Series, 138, 83–106.
Hodge, M., J. Biggs, K. Goda, and W. Aspinall (2015), Assessing infrequent large earthquakes using geomorphology and geodesy: the Malawi Rift, Natural hazards (Dordrecht, Netherlands), 76(3), 1781–1806, doi: 10.1007/s11069-014-1572-y.
Hodge, M., A. Fagereng, J. Biggs, and H. Mdala (2018), Controls on early-rift geometry: New perspectives from the bilila-mtakataka fault, Malawi, Geophysical research letters, 45(9), 3896–3905, doi: 10.1029/2018gl077343.
Hodge, M., J. Biggs, A. Fagereng, H. Mdala, L. N. J. Wedmore, and J. N. Williams (2020), Evidence from high-resolution topography for multiple earthquakes on high slip-to-length fault scarps: The Bilila-Mtakataka fault, Malawi, Tectonics, 39(2), e2019TC005,933, doi: 10.1029/2019tc005933.
Hodgson, I., F. Illsley-Kemp, R. J. Gallacher, D. Keir, C. J. Ebinger, and K. Mtelela (2017), Crustal Structure at a Young Continental Rift: A Receiver Function Study From the Tanganyika Rift, Tectonics, 36(12), 2806–2822, doi: 10.1002/2017TC004477.
Holmgren, J. M., M. J. Werner, K. Goda, M. Villani, V. Silva, P. Chindandali, and V. Stevens (2023), A relocated earthquake catalog and ground motion database for the southern East African rift system, Earthquake spectra : the professional journal of the Earthquake Engineering Research Institute, 39(3), 1911–1929, doi: 10.1177/87552930231173450.
Hopper, E., J. B. Gaherty, D. J. Shillington, N. J. Accardo, A. A. Nyblade, B. K. Holtzman, C. Havlin, A. Scholz, P. R. N. Chindandali, R. W. Ferdinand, G. D. Mulibo, and G. Mbogoni (2020), Preferential localized thinning of lithospheric mantle in the melt-poor Malawi Rift, Nature geoscience, 13(8), 584–589, doi: 10.1038/s41561-020-0609-y.
Ingleby, T., and T. J. Wright (2017), Omori-like decay of postseismic velocities following continental earthquakes: OMORI DECAY OF POSTSEISMIC VELOCITIES, Geophysical research letters, 44(7), 3119–3130, doi: 10.1002/2017gl072865.
Jackson, J., and T. Blenkinsop (1993), The Malaŵi Earthquake of March 10, 1989: Deep faulting within the East African Rift System, Tectonics, 12(5), 1131–1139, doi: 10.1029/93TC01064.
Jackson, J., and T. Blenkinsop (1997), The Bilila-Mtakataka fault in Malaŵi: An active, 100-km long, normal fault segment in thick seismogenic crust, Tectonics, 16(1), 137–150, doi: 10.1029/96tc02494.
Jackson, J., D. A. N. McKENZIE, K. Priestley, and B. Emmerson (2008), New views on the structure and rheology of the lithosphere, Journal of the Geological Society, 165(2), 453–465, doi: 10.1144/0016-76492007-109.
Jamtveit, B., Y. Ben-Zion, F. Renard, and H. Austrheim (2018), Earthquake-induced transformation of the lower crust, Nature, 556(7702), 487–491, doi: 10.1038/s41586-018-0045-y.
Jess, S., D. Koehn, M. Fox, E. Enkelmann, T. Sachau, and K. Aanyu (2020), Paleogene initiation of the Western Branch of the East African Rift: The uplift history of the Rwenzori Mountains, Western Uganda, Earth and planetary science letters, 552(116593), 116,593, doi: 10.1016/j.epsl.2020.116593.
Julià, J., C. J. Ammon, and A. A. Nyblade (2005), Evidence for mafic lower crust in Tanzania, East Africa, from joint inversion of receiver functions and Rayleigh wave dispersion velocities, Geophysical journal international, 162(2), 555–569, doi: 10.1111/j.1365-246X.2005.02685.x.
Kachingwe, M., A. Nyblade, and J. Julià (2015), Crustal structure of Precambrian terranes in the southern African subcontinent with implications for secular variation in crustal genesis, Geophysical journal international, 202(1), 533–547, doi: 10.1093/gji/ggv136.
Kendall, J.-M., and C. Lithgow-Bertelloni (2016), Why is Africa rifting?, Geological Society special publication, 420(1), 11–30, doi: 10.1144/sp420.17.
Kinabo, B. D., J. P. Hogan, E. A. E. A. Atekwana, M. G. Abdelsalam, and M. P. Modisi (2008), Fault growth and propagation during incipient continental rifting: Insights from a combined aeromagnetic and Shuttle Radar Topography Mission digital elevation model investigation of the Okavango Rift Zone, northwest Botswana, Tectonics, 27 (3), 1–16, doi: 10.1029/2007TC002154.
Kirby, S. H., and A. K. Kronenberg (1987), Correction to “Rheology of the lithosphere: Selected topics”, Reviews of geophysics (Washington, D.C.: 1985), 25(8), 1680–1681, doi: 10.1029/rg025i008p01680.
Kohlstedt, D. L., B. Evans, and S. J. Mackwell (1995), Strength of the lithosphere: Constraints imposed by laboratory experiments, Journal of geophysical research, 100(B9), 17,587–17,602, doi: 10.1029/95JB01460.
Kolawole, F., and R. Ajala (2024), Propagating rifts: the roles of crustal damage and ascending mantle fluids, Solid earth, 15(7), 747–762, doi: 10.5194/se-15-747-2024.
Kolawole, F., E. A. Atekwana, S. Malloy, D. S. Stamps, R. Grandin, M. G. Abdelsalam, K. Leseane, and E. M. Shemang (2017), Aeromagnetic, gravity, and Differential Interferometric Synthetic Aperture Radar analyses reveal the causative fault of the 3 April 2017 Mw 6.5 Moiyabana, Botswana, earthquake: Mw6.5 Botswana Earthquake Fault Revealed, Geophysical research letters, 44(17), 8837–8846, doi: 10.1002/2017gl074620.
Lavayssière, A., C. Drooff, C. Ebinger, R. Gallacher, F. Illsley-Kemp, S. J. Oliva, and D. Keir (2019), Depth Extent and Kinematics of Faulting in the Southern Tanganyika Rift, Africa, Tectonics, 38(3), 842–862, doi: 10.1029/2018TC005379.
Lindenfeld, M., G. Rümpker, A. Batte, and A. Schumann (2012a), Seismicity from February 2006 to September 2007 at the Rwenzori Mountains, East African Rift: earthquake distribution, magnitudes and source mechanisms, Solid earth, 3(2), 251–264, doi: 10.5194/se-3-251-2012.
Lindenfeld, M., G. Rümpker, K. Link, D. Koehn, and A. Batte (2012b), Fluid-triggered earthquake swarms in the Rwenzori region, East African Rift—Evidence for rift initiation, Tectonophysics, 566-567, 95–104, doi: 10.1016/j.tecto.2012.07.010.
Lloyd, R., J. Biggs, and A. Copley (2019), The decade-long Machaze–Zinave aftershock sequence in the slowly straining Mozambique Rift, Geophysical journal international, 217 (1), 504–531, doi: 10.1093/gji/ggz033.
Macheyeki, A. S., H. Mdala, L. S. Chapola, V. J. Manhiça, J. Chisambi, P. Feitio, A. Ayele, J. Barongo, R. W. Ferdinand, G. Ogubazghi, B. Goitom, J. D. Hlatywayo, G. K. Kianji, I. Marobhe, A. Mulowezi, D. Mutamina, J. M. Mwano, B. Shumba, and I. Tumwikirize (2015), Active fault mapping in Karonga-Malawi after the December 19, 2009 Ms 6.2 seismic event, Journal of African earth sciences (Oxford, England: 1994), 102, 233–246, doi: 10.1016/j.jafrearsci.2014.10.010.
Mackintosh, V., B. Kohn, A. Gleadow, and K. Gallagher (2019), Long-term reactivation and morphotectonic history of the Zambezi Belt, northern Zimbabwe, revealed by multi-method thermochronometry, Tectonophysics, 750(vember 2018), 117–136, doi: 10.1016/j.tecto.2018.11.009.
Mackwell, S. J., M. E. Zimmerman, and D. L. Kohlstedt (1998), High-temperature deformation of dry diabase with application to tectonics on Venus, Journal of geophysical research, 103(B1), 975–984, doi: 10.1029/97jb02671.
Magistrale, H. (2001), Relative contributions of crustal temperature and composition to controlling the depth of earthquakes in Southern California, Geophysical research letters, 29(10), 81–87, doi: 10.1029/2001GL014375.
Manda, B. W. C., P. A. Cawood, C. J. Spencer, T. Prave, R. Robinson, and N. M. W. Roberts (2019), Evolution of the Mozambique Belt in Malawi constrained by granitoid U-Pb, Sm-Nd and Lu-Hf isotopic data, Gondwana research: international geoscience journal, 68, 93–107, doi: 10.1016/j.gr.2018.11.004.
Mckenzie, D., J. Jackson, and K. Priestley (2005), Thermal structure of oceanic and continental lithosphere, Earth and planetary science letters, 233(3-4), 337–349, doi: 10.1016/j.epsl.2005.02.005.
Meghraoui, M., and the IGCP-601 Working Group (2016), The seismotectonic map of Africa, Episodes, 39(1), 9–18, doi: 10.18814/epiiugs/2016/v39i1/89232.
Midzi, V., I. Saunders, B. Manzunzu, M. T. Kwadiba, V. Jele, R. Mantsha, K. T. Marimira, T. F. Mulabisana, O. Ntibinyane, T. Pule, G. W. Rathod, M. Sitali, L. Tabane, G. van Aswegen, and B. S. Zulu (2018), The 03 April 2017 Botswana M6.5 earthquake: Preliminary results, Journal of African earth sciences (Oxford, England: 1994), 143(April 2017), 187–194, doi: 10.1016/j.jafrearsci.2018.03.027.
Montési, L. G. J. (2004), Controls of shear zone rheology and tectonic loading on postseismic creep: TIME DEPENDENCE OF POSTSEISMIC CREEP, Journal of geophysical research, 109(B10), doi: 10.1029/2003jb002925.
Moorkamp, M., S. Fishwick, R. J. Walker, and A. G. Jones (2019), Geophysical evidence for crustal and mantle weak zones controlling intra-plate seismicity – the 2017 Botswana earthquake sequence, Earth and planetary science letters, 506, 175–183, doi: 10.1016/j.epsl.2018.10.048.
Muirhead, J. D., L. J. M. Wright, and C. A. Scholz (2019), Rift evolution in regions of low magma input in East Africa, Earth and planetary science letters, 506, 332–346, doi: 10.1016/j.epsl.2018.11.004.
Muluneh, A. A., D. Keir, and G. Corti (2021), Thermo-rheological properties of the Ethiopian lithosphere and evidence for transient fluid induced lower crustal seismicity beneath the Ethiopian rift, Frontiers in earth science, 9(May), 1–11, doi: 10.3389/feart.2021.610165.
Nair, S. K., S. S. Gao, K. H. Liu, and P. G. Silver (2006), Southern African crustal evolution and composition: Constraints from receiver function studies, Journal of geophysical research. Solid earth, 111(2), 1–17, doi: 10.1029/2005JB003802.
Nishimura, K., S. Uehara, and K. Mizoguchi (2019), An alternative origin of high VP/Vs anomalies in slow slip regions: Experimental constraints from the elastic wave velocity evolution of highly fractured rock, Journal of geophysical research. Solid earth, 124(5), 5045–5059, doi: 10.1029/2018jb016929.
Njinju, E. A., E. A. Atekwana, D. S. Stamps, M. G. Abdelsalam, E. A. Atekwana, K. L. Mickus, S. Fishwick, F. Kolawole, T. A. Rajaonarison, and V. N. Nyalugwe (2019a), Lithospheric structure of the Malawi rift: Implications for magma-poor rifting processes, Tectonics, 38(11), 3835–3853, doi: 10.1029/2019tc005549.
Njinju, E. A., F. Kolawole, E. A. Atekwana, D. S. Stamps, E. A. Atekwana, M. G. Abdelsalam, and K. L. Mickus (2019b), Terrestrial heat flow in the Malawi Rifted Zone, East Africa: Implications for tectono-thermal inheritance in continental rift basins, Journal of volcanology and geothermal research, 387 (106656), 106,656, doi: 10.1016/j.jvolgeores.2019.07.023.
Nyblade, A. A., and C. A. Langston (1995), East African earthquakes below 20 km depth and their implications for crustal structure, Geophysical journal international, 121(1), 49–62, doi: 10.1111/j.1365-246X.1995.tb03510.x.
Nyblade, A. A., H. N. Pollack, D. L. Jones, F. Podmore, and M. Mushayandebvu (1990), Terrestrial heat flow in east and southern Africa, Journal of geophysical research, 95(B11), 17,371–17,384, doi: 10.1029/jb095ib11p17371.
Paulssen, H., T. Micallef, D. R. Bouwman, E. Ruigrok, M. W. Herman, I. Fadel, M. van der Meijde, M. Kwadiba, J. Maritinkole, and O. Ntibinyane (2022), Rifting of the Kalahari craton through Botswana? New seismic evidence, Journal of geophysical research. Solid earth, 127 (4), doi: 10.1029/2021jb023524.
Petersen, T., K. Gledhill, M. Chadwick, N. H. Gale, and J. Ristau (2011), The New Zealand National Seismograph Network, Seismological research letters, 82(1), 9–20, doi: 10.1785/gssrl.82.1.9.
Poggi, V., R. Durrheim, G. M. Tuluka, G. Weatherill, R. Gee, M. Pagani, A. Nyblade, and D. Delvaux (2017), Assessing seismic hazard of the East African Rift: a pilot study from GEM and AfricaArray, Bulletin of earthquake engineering, 15(11), 4499–4529, doi: 10.1007/s10518-017-0152-4.
Rajaonarison, T., D. S. Stamps, and J. Naliboff (2021), Role of lithospheric buoyancy forces in driving deformation in east Africa from 3D geodynamic modeling, Geophysical research letters, 48(6), e2020GL090,483, doi: 10.1029/2020GL090483.
Roberts, E. M., N. J. Stevens, P. M. O’Connor, P. H. G. M. Dirks, M. D. Gottfried, W. C. Clyde, R. A. Armstrong, A. I. S. Kemp, and S. Hemming (2012), Initiation of the western branch of the East African Rift coeval with the eastern branch, Nature geoscience, 5(4), 289–294, doi: 10.1038/ngeo1432.
Roecker, S., C. Ebinger, C. Tiberi, G. Mulibo, R. Ferdinand-Wambura, K. Mtelela, G. Kianji, A. Muzuka, S. Gautier, J. Albaric, and S. Peyrat (2017), Subsurface images of the Eastern Rift, Africa, from the joint inversion of body waves, surface waves and gravity: investigating the role of fluids in early-stage continental rifting, Geophysical journal international, 210(2), 931–950, doi: 10.1093/gji/ggx220.
Rolandone, F., R. Bürgmann, and R. M. Nadeau (2004), The evolution of the seismic-aseismic transition during the earthquake cycle: Constraints from the time-dependent depth distribution of aftershocks: AN EVOLVING SEISMIC-ASEISMIC TRANSITION, Geophysical research letters, 31(23), 1–4, doi: 10.1029/2004gl021379.
Rosenberg, C. L., and M. R. Handy (2005), Experimental deformation of partially melted granite revisited: implications for the continental crust, Journal of metamorphic geology, 23(1), 19–28, doi: 10.1111/j.1525-1314.2005.00555.x.
Rutter, E. H., and K. H. Brodie (2004), Experimental grain size-sensitive flow of hot-pressed Brazilian quartz aggregates, Journal of Structural Geology, 26(11), 2011–2023, doi: 10.1016/j.jsg.2004.04.006.
Rybacki, E., and G. Dresen (2000), Dislocation and diffusion creep of synthetic anorthite aggregates, Journal of geophysical research. Solid earth, 105(B11), 26,017–26,036, doi: 10.1029/2000JB900223.
Saria, E., E. Calais, D. S. Stamps, D. Delvaux, and C. J. H. Hartnady (2014), Present-day kinematics of the east African rift, Journal of geophysical research. Solid earth, 119(4), 3584–3600, doi: 10.1002/2013jb010901.
Shillington, D. J., C. A. Scholz, P. R. N. Chindandali, J. B. Gaherty, N. J. Accardo, E. Onyango, C. J. Ebinger, and A. A. Nyblade (2020), Controls on rift faulting in the North Basin of the Malawi (Nyasa) rift, east Africa, Tectonics, 39(3), e2019TC005,633, doi: 10.1029/2019tc005633.
Shudofsky, G. N., S. Cloetingh, S. Stein, and R. Wortel (1987), Unusually deep earthquakes in East Africa: Constraints on the thermo-mechanical structure of a continental rift system, Geophysical research letters, 14(7), 741–744, doi: 10.1029/gl014i007p00741.
Sibson, R. (1982), Fault zone models, heat flow, and the depth distribution of earthquakes in the continental crust of the United States, Bulletin of the Seismological Society of America, 72(1), 151–163.
Sibson, R. H. (1974), Frictional constraints on thrust, wrench and normal faults, Nature, 249(5457), 542–544, doi: 10.1038/249542a0.
Sibson, R. H. (2000), Fluid involvement in normal faulting, Journal of geodynamics, 29(3-5), 469–499, doi: 10.1016/s0264-3707(99)00042-3.
Sibson, R. H., and J. V. Rowland (2003), Stress, fluid pressure and structural permeability in seismogenic crust, North Island, New Zealand, Geophysical journal international, 154(2), 584–594, doi: 10.1046/j.1365-246X.2003.01965.x.
Stamps, D. S., L. M. Flesch, E. Calais, and A. Ghosh (2014), Current kinematics and dynamics of Africa and the East African Rift System, Journal of geophysical research. Solid earth, 119(6), 5161–5186, doi: 10.1002/2013jb010717.
Stamps, D. S., C. Kreemer, R. Fernandes, T. A. Rajaonarison, and G. Rambolamanana (2021), Redefining East African Rift System kinematics, Geology, 49(2), 150–155, doi: 10.1130/g47985.1.
Stein, S., and M. Liu (2009), Long aftershock sequences within continents and implications for earthquake hazard assessment, Nature, 462(7269), 87–89, doi: 10.1038/nature08502.
Stevens, V. L., R. A. Sloan, P. R. Chindandali, L. N. J. Wedmore, G. W. Salomon, and R. A. Muir (2021), The Entire Crust can be Seismogenic: Evidence from Southern Malawi, Tectonics, 40(6), doi: 10.1029/2020tc006654.
Sun, M., S. S. Gao, K. H. Liu, K. Mickus, X. Fu, and Y. Yu (2021), Receiver function investigation of crustal structure in the Malawi and Luangwa rift zones and adjacent areas, Gondwana research: international geoscience journal, 89, 168–176, doi: 10.1016/j.gr.2020.08.015.
Tugume, F., A. Nyblade, and J. Julià (2012), Moho depths and Poisson’s ratios of Precambrian crust in East Africa: Evidence for similarities in Archean and Proterozoic crustal structure, Earth and planetary science letters, 355-356, 73–81, doi: 10.1016/j.epsl.2012.08.041.
Tulley, C. J., A. Fagereng, and K. Ujiie (2020), Hydrous oceanic crust hosts megathrust creep at low shear stresses, Science advances, 6(22), eaba1529, doi: 10.1126/sciadv.aba1529.
Von Herzen, R. P., and V. Vacquier (1967), Terrestrial heat flow in Lake Malawi, Africa, Journal of geophysical research, 72(16), 4221–4226, doi: 10.1029/JZ072i016p04221.
Wanke, H. (2005), The Namibian Eiseb Graben as an extension of the East African Rift: evidence from Landsat TM 5 imagery, Suid-Afrikaanse tydskrif vir geologie [South African journal of geology], 108(4), 541–546, doi: 10.2113/108.4.541.
Wedmore, L. N. J., J. Biggs, J. N. Williams, A. Fagereng, Z. Dulanya, F. Mphepo, and H. Mdala (2020a), Active fault scarps in southern Malawi and their implications for the distribution of strain in incipient continental rifts, Tectonics, 39(3), e2019TC005,834, doi: 10.1029/2019tc005834.
Wedmore, L. N. J., J. N. Williams, J. Biggs, A. Fagereng, F. Mphepo, Z. Dulanya, J. Willoughby, H. Mdala, and B. A. Adams (2020b), Structural inheritance and border fault reactivation during active early-stage rifting along the Thyolo fault, Malawi, Journal of structural geology, 139(104097), 104,097, doi: 10.1016/j.jsg.2020.104097.
Wedmore, L. N. J., J. Biggs, M. Floyd, A. Fagereng, H. Mdala, P. Chindandali, J. N. Williams, and F. Mphepo (2021), Geodetic constraints on cratonic microplates and broad strain during rifting of thick southern African lithosphere, Geophysical research letters, 48(17), doi: 10.1029/2021gl093785.
Wedmore, L. N. J., T. Turner, J. Biggs, J. N. Williams, H. M. Sichingabula, C. Kabumbu, and K. Banda (2022), The Luangwa Rift Active Fault Database and fault reactivation along the southwestern branch of the East African Rift, Solid earth, 13(11), 1731–1753, doi: 10.5194/se-13-1731-2022.
Wedmore, L. N. J., D. Evans, J. N. Williams, J. Biggs, A. Fagereng, P. Mawejje, F. Tugume, T. Blenkinsop, and E. J. Hobley (2024), The early onset of magmatic rift faulting in the Edward-George Rift, Uganda, Earth and planetary science letters, 638(118762), 118,762, doi: 10.1016/j.epsl.2024.118762.
Wilks, K. R., and N. L. Carter (1990), Rheology of some continental lower crustal rocks, Tectonophysics, 182(1-2), 57–77, doi: 10.1016/0040-1951(90)90342-6.
Williams, J. N., A. Fagereng, L. N. J. Wedmore, J. Biggs, F. Mphepo, Z. Dulanya, H. Mdala, and T. Blenkinsop (2019), How Do Variably Striking Faults Reactivate During Rifting? Insights From Southern Malawi, Geochemistry, geophysics, geosystems: G(3), 20(7), 3588–3607, doi: 10.1029/2019GC008219.
Williams, J. N., L. N. J. Wedmore, C. A. Scholz, F. Kolawole, L. J. M. Wright, D. J. Shillington, A. Fagereng, J. Biggs, H. Mdala, Z. Dulanya, F. Mphepo, P. R. N. Chindandali, and M. J. Werner (2022a), The Malawi active fault database: An onshore-offshore database for regional assessment of seismic hazard and tectonic evolution, Geochemistry, geophysics, geosystems: G(3), 23(5), e2022GC010,425, doi: 10.1029/2022gc010425.
Williams, J. N., A. Fagereng, L. N. J. Wedmore, J. Biggs, H. Mdala, F. Mphepo, and M. Hodge (2022b), Low dissipation of earthquake energy where a fault follows pre-existing weaknesses: Field and microstructural observations of Malawi’s bilila-mtakataka fault, Geophysical research letters, 49(8), e2021GL095,286, doi: 10.1029/2021gl095286.
Williams, J. N., L. N. J. Wedmore, A. Fagereng, M. J. Werner, H. Mdala, D. J. Shillington, C. A. Scholz, F. Kolawole, L. J. M. Wright, J. Biggs, Z. Dulanya, F. Mphepo, and P. Chindandali (2022c), 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), 3607–3639, doi: 10.5194/nhess-22-3607-2022.
Williams, J. N., M. J. Werner, K. Goda, L. N. J. Wedmore, R. De Risi, J. Biggs, H. Mdala, Z. Dulanya, A. Fagereng, F. Mphepo, and P. Chindandali (2023), Fault-based probabilistic seismic hazard analysis in regions with low strain rates and a thick seismogenic layer: a case study from Malawi, Geophysical journal international, 233(3), 2172–2207, doi: 10.1093/gji/ggad060.
Williams, J. N., D. Eberhart-Phillips, S. Bourguignon, M. W. Stirling, and W. Oliver (2025), Deep and clustered microseismicity at the edge of southern new zealand’s transpressive plate boundary, Journal of geophysical research. Solid earth, 130(5), e2024JB030,371, doi: 10.1029/2024jb030371.
Wintsch, R. P., R. Christoffersen, and A. K. Kronenberg (1995), Fluid-rock reaction weakening of fault zones, Journal of geophysical research, 100(B7), 13,021–13,032, doi: 10.1029/94jb02622.
Wood, D. A., H. J. Zal, C. A. Scholz, C. J. Ebinger, and I. Nizere (2017), Evolution of the Kivu Rift, East Africa: interplay among tectonics, sedimentation and magmatism, Basin research, 29, 175–188, doi: 10.1111/bre.12143.
Wright, T., J. Elliott, H. Wang, and I. Ryder (2013), Earthquake cycle deformation and the Moho: Implications for the rheology of continental lithosphere, Tectonophysics, 609, 504–523, doi: 10.1016/J.TECTO.2013.07.029.
Yang, Z., and W.-P. Chen (2010), Earthquakes along the East African Rift System: A multiscale, system-wide perspective, Journal of geophysical research, 115(B12), doi: 10.1029/2009jb006779.
Yu, Y., K. H. Liu, C. A. Reed, M. Moidaki, K. Mickus, A. Atekwana, and S. S. Gao (2015), A joint receiver function and gravity study of crustal structure beneath the incipient Okavango Rift, Botswana, Geophysical research letters, 42(20), 8398–8405, doi: 10.1002/2015gl065811.
Zertani, S., M. Thielmann, and L. Menegon (2025), Lower-crustal earthquakes: Strain rate controls the magnitude and rate of stress amplification in rigid blocks, Geophysical research letters, 52(7), doi: 10.1029/2024gl114350.