Evidence for an Intermediate Layer from Crustal Structure Studies in the Eastern Transvaal.

Hales, A. L.; Sacks, I. Selwyn

doi:10.1111/j.1365-246x.1959.tb05777.x

Cited by 64 publications

(19 citation statements)

References 12 publications

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“…As found in earlier Australian work, P2 may not be a first arrival at any distance in many regions. This would give limits to any intermediate layer thickness (Hales and Sacks, 1959).…”

Section: Pimentioning

confidence: 98%

Seismic velocities and crustal structure in southern Australia

Doyle

Everingham

1964

Journal of the Geological Society of Australia

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“…As found in earlier Australian work, P2 may not be a first arrival at any distance in many regions. This would give limits to any intermediate layer thickness (Hales and Sacks, 1959).…”

Section: Pimentioning

confidence: 98%

Seismic velocities and crustal structure in southern Australia

Doyle

Everingham

1964

Journal of the Geological Society of Australia

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“…1956;Hales & Sacks 1959). Since the advent of semiconductor electronics and digital computers in the 1960s there have been dramatic advances in seismograph design, signal processing and seismic interpretation techniques.…”

Section: Introductionmentioning

confidence: 99%

A seismic refraction investigation of the Archaean Kaapvaal Craton, South Africa, using mine tremors as the energy source

Durrheim

Green

1992

Geophysical Journal International

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S U M M A R YThe structure of the central Kaapvaal Craton of southern Africa has been investigated by deep seismic sounding, using mine tremors as energy sources. Seismometers were deployed at approximately 10 km intervals on two profiles stretching between major mine tremor source regions. Mine tremors are rich in shear energy enabling joint interpretation of P-and S-waves and produce substantial energy at frequencies as low as 1 Hz. Record sections are presented for both P-and S-waves, and the traveltimes and amplitudes interpreted using 2-D ray-tracing techniques. Synthetic seismograms computed for a 1-D velocity model by the reflectivity method compare well with the observed data. A generalized seismic model of the Kaapvaal Craton has the following features: supracrustal strata 0-10 km thick; upper crystalline basement with P-wave velocities of 6.0-6.2 km s-'; the boundary between upper and lower crust at a depth of 14-18 km; a lower crust with a relatively uniform seismic velocity in the range 6.4-6.7 kms-'; and the crust/mantle transition over 1-3 km with the Moho at a depth of about 35 km. The lower crust is found to be seismically attenuating and has a Poisson's ratio of about 0.28. It is also known to be electrically conductive. These observations are in accord with the presence of hydrated mantle rock at the base of the crust.The velocity-depth model of the Kaapvaal Craton is similar to models derived for other Archaean cratons. The Proterozoic provinces adjacent to the Kaapvaal craton are significantly thicker, and have an intermediate-to high-velocity layer developed at the base of the crust. This is interpreted to indicate a change in the process of crustal growth, with basaltic underplating becoming more important since the Archaean. This change is attributed to a change in the composition of the upper mantle. The higher temperatures in the Archaean mantle led to the eruption of komatiitic lavas, resulting in an ultradepleted mantle unable to produce significant volumes of basaltic melt. Proterozoic crust developed above fertile mantle, and subsequent partial melting resulted in basaltic underplating and crustal inflation.

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“…Two more large arrivals follow, making five apparently distinct arrivals within the first 0'8 second. This pattern of arrivals is to be seen in many reports of crustal investigations (for example, Willmore and others, 1952;Hales and Sacks, 1959;Godin and others, 1961;Research Group for Explosion Seismology, Japan, 1951). In fact, it is difficult to find records that do not show many apparently distinct arrivals in the first second of arrival of energy.…”

Section: Introductionmentioning

confidence: 72%

On crustal structure deduced from seismic time-distance curves

Green

Steinhart

1962

New Zealand Journal of Geology and Geophysics

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The numerical computation of the time-distance curves for several quite different velocity-depth functions shows that first arrivals are not sufficient to determine the velocity-depth function. Minor second-order fluctuations in velocity superimposed on a general velocity gradient in the crust give a travel-time curve with multiple arrivals separated by fractions of a second. These initial bursts of multiple arrivals are observed in explosion seismology for shot-point ranges out to 450 km. With observed seismic data the position and amplitudes of the late arrivals and especially cusp points determine the general details of the crustal structure.

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Evidence for an Intermediate Layer from Crustal Structure Studies in the Eastern Transvaal.

Cited by 64 publications

References 12 publications

Seismic velocities and crustal structure in southern Australia

Seismic velocities and crustal structure in southern Australia

A seismic refraction investigation of the Archaean Kaapvaal Craton, South Africa, using mine tremors as the energy source

On crustal structure deduced from seismic time-distance curves

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