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

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

Research output: Contribution to journalArticlepeer-review

24 Scopus citations

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.

Original languageEnglish (US)
Pages (from-to)1892-1905
Number of pages14
JournalGeophysical Journal International
Volume209
Issue number3
DOIs
StatePublished - Jun 2017

Keywords

  • Continental tectonics: extensional
  • Free oscillations
  • Seismic instruments
  • Seismic noise
  • Seismic tomography
  • Surface waves

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

Fingerprint Dive into the research topics of 'Surface wave imaging of the weakly extended Malawi Rift from ambient-noise and teleseismic Rayleigh waves from onshore and lake-bottom seismometers'. Together they form a unique fingerprint.

Cite this