Pn wave velocities beneath the Tanzania Craton and adjacent rifted mobile belts, east Africa

Brazier, Richard; Nyblade, A.; Langston, Charles A.; Owens, Thomas

doi:10.1029/2000gl011586

Cited by 23 publications

(31 citation statements)

References 21 publications

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“…Figure 3 shows results from a regression analysis of the Pn travel times for the events of Table 1, and Table 2 displays the numerical results. As Brazier et al [2000] point out using a tomographic Pn velocity within the network is quite high at 8.2 -8.5 km/s, with the higher velocities found within the craton. The regression analysis shown in Figure 3 and Table 2 is consistent with their result.…”

Section: Esementioning

confidence: 75%

“…Thus there is evidence of velocity heterogeneity that cannot be modeled by these methods at present. Brazier et al [2000] performed a Pn tomography and showed $4% heterogeneity in Pn velocities between cratonic and Mozambique belt upper mantle. There is probably similar heterogeneity in crustal velocity and thickness.…”

Section: Discussionmentioning

confidence: 99%

“…The network was designed to record teleseismic body waves and surface waves to determine large-scale crust and upper mantle structure Nyblade et al, 1996]. A number of studies have been completed using data from this experiment, including analysis of teleseismic receiver functions for crustal structure [Last et al, 1997], P and S wave mantle tomography [Ritsema et al, 1998], seismicity studies [Nyblade et al, 1996;Langston et al, 1998], Pn tomography [Brazier et al, 2000], and study of upper mantle discontinuities from receiver function stacking . In addition, new gravity measurements were made to fill in the gravity map of Tanzania and to add constraints on crustal thickness estimates [Tesha et al, 1997].…”

Section: Introductionmentioning

confidence: 99%

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Regional wave propagation in Tanzania, East Africa

2002

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[1] Crust and upper mantle structure under Tanzania, East Africa, is investigated using broadband waveforms and phase travel times collected from regional events recorded by the 1994 -1995 Tanzania Broadband Seismic Experiment. Broadband displacement waveforms from the mL 5.9 Rukwa graben earthquake (18 August 1994) are modeled using a wave number integration algorithm and a new ''phase time'' inversion technique to infer a very simple crustal and upper mantle model that can be used for waveform studies of other regional earthquakes in the area. Displacement amplitudes for all phases in the data are predicted quite well using source parameters determined from a previous study of teleseismic waveforms. The crust is parameterized by a linear gradient in velocity defined by surface and Moho P velocities, Poisson's ratio, and crustal thickness. This simple parameterization is sufficient to explain arrival times and waveshapes of the three-component waveforms recorded between 200 and 800 km at stations located on the craton and Mozambique belt. The S wave train consists of Sn, multiple Sn, and critically reflected S wave multiples in the crustal waveguide, in addition to the fundamental mode Rayleigh wave. High phase velocity, critical S wave reflections are seen to form the low group velocity Lg phase. Prominent sP depth phases are seen in the regional waveform data which can be used to infer accurate source depths for events in the region. The Tanzania craton and adjacent Mozambique belt crustal structure is simple and laterally homogeneous, showing few effects of rift disruption. High wave velocities in the uppermost mantle suggest little thermal modification from rifting processes of the East African Rift.

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Section: Esementioning

confidence: 75%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Regional wave propagation in Tanzania, East Africa

2002

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“…We used a simple velocity model derived from previous studies in the area, including seismic refractions in south Kenya (KRISP, 1991;Birt et al, 1997;Prodehl et al, 1997), receiver function analysis (Last et al, 1997;Julia et al, 2005) and P n travel time inversion (Brazier et al, 2000;Nyblade and Brazier, 2002). It consists of three crustal layers with V p ¼ 5:9 km s À1 from 0 to 14 km depth, V p ¼ 6:5 km s À1 from 14 to 27 km and V p ¼ 6:8 km s À1 from 27 to 37 km depth.…”

Section: Data Processingmentioning

confidence: 99%

Contrasted seismogenic and rheological behaviours from shallow and deep earthquake sequences in the North Tanzanian Divergence, East Africa

Albaric¹,

Perrot²,

Déverchère³

et al. 2010

Journal of African Earth Sciences

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“…P wave travel times from regional earthquakes were inverted for longwavelength (>100 km) Pn velocity variations beneath Tanzania by Brazier et al [2000]. They found Pn velocities of $8.4 km/s beneath the center of the Tanzania craton, 8.3 km/s beneath the Mozambique Belt where the Eastern Rift terminates, and 8.4 km/s beneath the Western Rift.…”

Section: Tanzaniamentioning

confidence: 99%

On the relationship between extension and anisotropy: Constraints from shear wave splitting across the East African Plateau

et al. 2004

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[1] East Africa is a tectonically complex region owing to the presence of a rigid craton, paleothrust belts and shear zones, active magmatism and rifting, and possibly even a mantle plume. We present new splitting results of teleseismic shear phases recorded by 21 broadband seismic stations in Tanzania, seven broadband stations in Kenya, and three permanent broadband Global Seismic Network stations in Kenya and Uganda. Inconsistent apparent splitting is observed beneath the craton and along its southern and southeastern flank in Tanzania. Splitting at stations elsewhere in the rifts and orogenic belts is more consistent. We test between different models of anisotropy for stations with inconsistent splitting (single layer with horizontal fast axis, single layer with dipping fast axis, and two layers with horizontal fast axes). However, we show that these more complicated models do not reasonably explain the data. The data are explained better by a laterally (and/or in some places vertically) varying single-layer model with a horizontal fast axis. We arrive at a conceptual model of anisotropy in Tanzania and Kenya that is controlled by (1) active shear along the base of the plate associated with asthenospheric flow beneath and around the moving craton keel, (2) asthenospheric flow from a plume north of central Kenya, (3) fossilized anisotropy in the lithosphere due to past orogenic events, and possibly (4) aligned magma-filled lenses beneath the rifts. Our most robust conclusion is that we can rule out an extension-induced lattice preferred orientation of olivine as a dominant factor, which is surprising given the long history of extension in the region. This indicates that mantle-lithospheric extension in East Africa occurs via dikeintrusion and/or ductile thinning within narrow rift zones and is possibly facilitated by a mechanical lithospheric anisotropy imparted by fossilized north/south structural or mineralogical fabrics.

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Pn wave velocities beneath the Tanzania Craton and adjacent rifted mobile belts, east Africa

Cited by 23 publications

References 21 publications

Regional wave propagation in Tanzania, East Africa

Regional wave propagation in Tanzania, East Africa

Contrasted seismogenic and rheological behaviours from shallow and deep earthquake sequences in the North Tanzanian Divergence, East Africa

On the relationship between extension and anisotropy: Constraints from shear wave splitting across the East African Plateau

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