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Surface wave imaging of the weakly extended Malawi Rift from ambient-noise and teleseismic Rayleigh waves from onshore and lake-bottom seismometers

Surface wave imaging of the weakly extended Malawi Rift from ambient-noise and teleseismic Rayleigh waves from onshore and lake-bottom seismometers
Surface wave imaging of the weakly extended Malawi Rift from ambient-noise and teleseismic Rayleigh waves from onshore and lake-bottom seismometers
Located at the southernmost sector of the Western Branch of the East African Rift System, the Malawi Rift exemplifies an active, magma-poor, weakly extended continental rift. To investigate the controls on rifting, we image crustal and uppermost mantle structure beneath the region using ambient-noise and teleseismic Rayleigh-wave phase velocities between 9 and 100 s period. Our study includes six lake-bottom seismometers located in Lake Malawi (Nyasa), the first time seismometers have been deployed in any of the African rift lakes. Noise levels in the lake are lower than that of shallow oceanic environments and allow successful application of compliance corrections and instrument orientation determination. Resulting phase-velocity maps reveal slow velocities primarily confined to Lake Malawi at short periods (T <= 12 s), indicating thick sediments in the border-fault bounded rift basin. The slowest velocities occur within the Central Basin where Malawi Rift sedimentary strata may overlie older (Permo-Triassic) Karoo group sediments. At longer periods (T > 25 s), a prominent low-velocity anomaly exists beneath the Rungwe Volcanic Province at the northern terminus of the rift basin. Estimates of phase-velocity sensitivity indicates these low velocities occur within the lithospheric mantle and potentially uppermost asthenosphere, suggesting that mantle processes may control the association of volcanic centres and the localization of magmatism. Beneath the main portion of the Malawi Rift, a modest reduction in velocity is also observed at periods sensitive to the crust and upper mantle, but these velocities are much higher than those observed beneath Rungwe.
0956-540X
1892-1905
Accardo, N.J.
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Gaherty, J.B.
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Shillington, D.J.
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Ebinger, C.J.
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Nyblade, A.A.
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Mbogoni, G.J.
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Chindandali, P.R.N.
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Ferdinand, R.W.
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Mulibo, G.D.
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Kamihanda, G.
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Keir, D.
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Scholz, C.
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Selway, K.
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O’Donnell, J.P.
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Tepp, G.
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Gallacher, R.
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Mtelela, K.
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Salima, J.
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Mruma, A.
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Accardo, N.J.
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Gaherty, J.B.
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Shillington, D.J.
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Ebinger, C.J.
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Nyblade, A.A.
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Mbogoni, G.J.
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Chindandali, P.R.N.
7048a07c-13ca-4c96-8837-1697b73f417d
Ferdinand, R.W.
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Mulibo, G.D.
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Kamihanda, G.
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Keir, D.
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Scholz, C.
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Selway, K.
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O’Donnell, J.P.
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Tepp, G.
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Gallacher, R.
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Mtelela, K.
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Salima, J.
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Mruma, A.
26c8da33-95a5-4c82-be57-d7930273d7d5

Accardo, N.J., Gaherty, J.B., Shillington, D.J., Ebinger, C.J., Nyblade, A.A., Mbogoni, G.J., Chindandali, P.R.N., Ferdinand, R.W., Mulibo, G.D., Kamihanda, G., Keir, D., Scholz, C., Selway, K., O’Donnell, J.P., Tepp, G., Gallacher, R., Mtelela, K., Salima, J. and Mruma, A. (2017) Surface wave imaging of the weakly extended Malawi Rift from ambient-noise and teleseismic Rayleigh waves from onshore and lake-bottom seismometers Geophysical Journal International, 209, (3), pp. 1892-1905. (doi:10.1093/gji/ggx133).

Record type: Article

Abstract

Located at the southernmost sector of the Western Branch of the East African Rift System, the Malawi Rift exemplifies an active, magma-poor, weakly extended continental rift. To investigate the controls on rifting, we image crustal and uppermost mantle structure beneath the region using ambient-noise and teleseismic Rayleigh-wave phase velocities between 9 and 100 s period. Our study includes six lake-bottom seismometers located in Lake Malawi (Nyasa), the first time seismometers have been deployed in any of the African rift lakes. Noise levels in the lake are lower than that of shallow oceanic environments and allow successful application of compliance corrections and instrument orientation determination. Resulting phase-velocity maps reveal slow velocities primarily confined to Lake Malawi at short periods (T <= 12 s), indicating thick sediments in the border-fault bounded rift basin. The slowest velocities occur within the Central Basin where Malawi Rift sedimentary strata may overlie older (Permo-Triassic) Karoo group sediments. At longer periods (T > 25 s), a prominent low-velocity anomaly exists beneath the Rungwe Volcanic Province at the northern terminus of the rift basin. Estimates of phase-velocity sensitivity indicates these low velocities occur within the lithospheric mantle and potentially uppermost asthenosphere, suggesting that mantle processes may control the association of volcanic centres and the localization of magmatism. Beneath the main portion of the Malawi Rift, a modest reduction in velocity is also observed at periods sensitive to the crust and upper mantle, but these velocities are much higher than those observed beneath Rungwe.

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Accepted/In Press date: 28 March 2017
e-pub ahead of print date: 1 April 2017

Identifiers

Local EPrints ID: 412802
URI: http://eprints.soton.ac.uk/id/eprint/412802
ISSN: 0956-540X
PURE UUID: bc7b51da-fce3-46d4-9aa9-749d175e0435
ORCID for D. Keir: ORCID iD orcid.org/0000-0001-8787-8446

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Date deposited: 02 Aug 2017 16:30
Last modified: 02 Nov 2017 17:31

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Contributors

Author: N.J. Accardo
Author: J.B. Gaherty
Author: D.J. Shillington
Author: C.J. Ebinger
Author: A.A. Nyblade
Author: G.J. Mbogoni
Author: P.R.N. Chindandali
Author: R.W. Ferdinand
Author: G.D. Mulibo
Author: G. Kamihanda
Author: D. Keir ORCID iD
Author: C. Scholz
Author: K. Selway
Author: J.P. O’Donnell
Author: G. Tepp
Author: R. Gallacher
Author: K. Mtelela
Author: J. Salima
Author: A. Mruma

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