The structure of the crust and upper mantle to depths of 320 km beneath the Kaapvaal craton, from P wave arrivals generated by regional earthquakes and mining-induced tremors

Wright, C.; Kwadiba, M. T. O.; Kgaswane, E.; Simon, Rapelang E.

doi:10.1016/s0899-5362(02)00157-4

Cited by 19 publications

(25 citation statements)

References 21 publications

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“…See Figure 3 As mentioned before, an alternative velocity model for South Africa was investigated by Midzi et al (2010); however, the resultant model did not notably improve the Wright (2002) model (Figure 3). The effect of different velocity models is equally considered with the network distribution of 1970 coupled with an earthquake depth centred at 5 km in the detection range 300, 500 and 1000 km.…”

Section: Eth O D O Lo G Ymentioning

confidence: 93%

“…1996). The three layered earth model of Wright et al (2002) replaced the two layered velocity model of Gane et al (1956) during September 2006 ). An investigation was undertaken by Midzi et al (2010) to further refine the ID velocity model for South Africa.…”

Section: The Roman Numerals On the Map Define Prom Inent Opencast Mmentioning

confidence: 99%

“…Three velocity models were considered as input: the Gane et al (1956); Wright et al (2002), and the VM1 model of Midzi et al (2010). See Figure 3 As mentioned before, an alternative velocity model for South Africa was investigated by Midzi et al (2010); however, the resultant model did not notably improve the Wright (2002) model (Figure 3).…”

Section: Eth O D O Lo G Ymentioning

confidence: 99%

“…Graham et al, 1991) and converted phases (Diehl et al, 2011). R esu lts a n d d is c u ssio n Examples of results obtained during this study considering the effect of velocity models (Gane et al, 1956;Wright et al, 2002 andMidzi et al, 2010), hypocentral depth, detection distance, phases and network layout are shown in Table 1 and presented as Figures 4 to 8. Figure 4 (a to c) illustrate the analysis of the three velocity models considered during this study.…”

Section: Determined the Average Statistical Evaluation O F Seism Ic Ementioning

confidence: 99%

“…It is evident that the errors in origin time and epicentre locations are similar, irrespective of the velocity model used. We selected the Wright et al (2002) model for the remainder of the study since it is the velocity model used during routine analysis of SANSN data (Saunders et al, 2006; The effect of vaiying hypocentral depths is shown as Figure 5 (a to c). The figures attest to subtle changes in the expected epicentre errors to the north of the SANSN, and also a slight variation in the expected error in origin time to the south.…”

Section: Determined the Average Statistical Evaluation O F Seism Ic Ementioning

confidence: 99%

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Statistical evaluation of seismic event location accuracy by the South African National Seismograph Network over four decades

Saunders

Kijko

Fourie

2016

South African Journal of Geology

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© 2 0 1 6 M arch G eo lo g ica l S o ciety o f Sou th A frica A b stractWe analyzed the changes/improvements of seismic event detection and location accuracy of the South African National Seismograph Network over the last four decades. The effect of three regional velocity models on epicentral solutions was tested during the initial study. It is shown that the hypocentral depth considered during this study, viz. at 2 km for mining related events, and 5 km to 10 km for tectonic earthquakes, have a negligible effect on the error in epicentre location. Further, three detection distances were evaluated during this study, viz. 300, 500 and 1000 km. The location errors decreased significantly by increasing the detecting distance. This study highlights the importance of including 5-phase arrival times to better constrain seismic event locations. This observation is of particular value for the 1970 to 1997 period, when only P-phases were considered during the location procedure. Lastly, it is shown how the errors in epicentre location decrease with an increase in the number and geographical distribution of seismic stations.

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Section: Eth O D O Lo G Ymentioning

confidence: 93%

Section: The Roman Numerals On the Map Define Prom Inent Opencast Mmentioning

confidence: 99%

Section: Eth O D O Lo G Ymentioning

confidence: 99%

Section: Determined the Average Statistical Evaluation O F Seism Ic Ementioning

confidence: 99%

Section: Determined the Average Statistical Evaluation O F Seism Ic Ementioning

confidence: 99%

See 3 more Smart Citations

Statistical evaluation of seismic event location accuracy by the South African National Seismograph Network over four decades

Saunders

Kijko

Fourie

2016

South African Journal of Geology

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Upper Mantle Seismic Structure Beneath Southern Africa: Constraints on the Buoyancy Supporting the African Superswell

Brandt

Grand

Nyblade

et al. 2011

Pure Appl. Geophys.

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We present new one-dimensional SH-wave velocity models of the upper mantle beneath the Kalahari craton in southern Africa obtained from waveform inversion of regional seismograms from an Mw = 5.9 earthquake located near Lake Tanganyika recorded on broadband seismic stations deployed during the 1997-1999 Southern African Seismic Experiment. The velocity in the lithosphere beneath the Kalahari craton is similar to that of other shields, and there is little evidence for a significant low velocity zone beneath the lithosphere. The lower part of the lithosphere, from 110 to 220 km depth, is slightly slower than beneath other shields, possibly due to higher temperatures or a decrease in Mg number (Mg#). If the slower velocities are caused by a thermal anomaly, then slightly less than half of the unusually high elevation of the Kalahari craton can be explained by shallow buoyancy from a hot lithosphere. However, a decrease in the Mg# of the lower lithosphere would increase the density and counteract the buoyancy effect of the higher temperatures. We obtain a thickness of 250 ± 30 km for the mantle transition zone, which is similar to the global average, but the velocity gradient between the 410 and 660 km discontinuities is less steep than in global models, such as PREM and IASP91. We also obtain velocity jumps of between 0.16 ± 0.1 and 0.21 ± 0.1 km/s across the 410 km discontinuity. Our results suggest that there may be a thermal or chemical anomaly in the mantle transition zone, or alternatively that the shear wave velocity structure of the transition zone in global reference models needs to be refined. Overall, our seismic models provide little support for an upper mantle source of buoyancy for the unusually high elevation of the Kalahari craton, and hence the southern African portion of the African Superswell.

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Relocation of 3 April 2017 Moiyabana Earthquake in Botswana Using Seismological Data from Local Network of Autonomously Recording Seismographs and International Monitoring System Stations

Simon,

King,

Moffat

et al. 2024

Pure Appl. Geophys.

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On the 3rd April 2017 a widely felt Moiyabana earthquake shook Botswana and the rest of southern Africa. Previous Moiyabana earthquake locations used mainly teleseismic or regional seismograms; and/or non-seismic methods which include Synthetic Aperture Radar (InSAR), and magnetotelluric (MT). These results did not agree, as evidenced by the depth of the earthquake that ranged from zero to 30 km (i.e. indicating either a man-made event or a natural event); thus motivating us to re-assess the location parameters. Unfiltered seismic waveform data from the recent project of the Network of Autonomously Recording Seismographs (NARS) in Botswana was complimented with stations from the International Monitoring System (IMS) to relocate the event. Relocated parameters are origin time, epicentre, focal depth, and magnitude. Geotool software from the Comprehensive Nuclear Test Ban Treaty Organization (CTBTO), and the Regional Seismic Travel Time model (RSTT) were used to process vertical components waveforms from 9 NARS and 32 IMS stations. Geotool results are: earthquake epicentre (22.645 °S: 25.220 °E); origin time of 17:40:16.9 (UTC); hypocentral depth range of 22 to 24 km; body magnitude (mb) and local magnitude (ml) of 6.3 ± 0.6 and 6.0 ± 0.8, respectively. RSTT results are: earthquake epicentre (22.667 °S: 25.257 °E); origin time of 17:40:16.95 (UTC); hypocentral depth of 25 km; and mb of 6.65 ± 0.03. The seismological location parameters from Geotool and RSTT, agree very well within experimental uncertainties with the non-seismic geophysical methods.

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The structure of the crust and upper mantle to depths of 320 km beneath the Kaapvaal craton, from P wave arrivals generated by regional earthquakes and mining-induced tremors

Cited by 19 publications

References 21 publications

Statistical evaluation of seismic event location accuracy by the South African National Seismograph Network over four decades

Statistical evaluation of seismic event location accuracy by the South African National Seismograph Network over four decades

Upper Mantle Seismic Structure Beneath Southern Africa: Constraints on the Buoyancy Supporting the African Superswell

Relocation of 3 April 2017 Moiyabana Earthquake in Botswana Using Seismological Data from Local Network of Autonomously Recording Seismographs and International Monitoring System Stations

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