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BERNARD PRICE INSTITUTE OF GEOPHYSICAL RESEARCH UNIVERSITY OF THE WITWATERSRAND, JOHANNESBURG, South Africa
DEPARTMENT OF GEODESY AND GEOPHYSICS UNIVERSITY OF CAMBRIDGE England
Abstract
Travel times are given as obtained from seismograms of the Witwatersrand earth tremors at distances up to 500 km. Five stations of several types were operated, which were moved as required. One method used continuous recording for a few hours daily; another used a triggering technique operated by radio from Johannesburg, where a network of six stations permitted the focus of each tremor to be located in time and place.
Readings from the 200 seismograms obtained give velocities V1 = 6.09 km/sec. and Vn = 8.27 km/sec. for the P1 and Pn phases, and v1 = 3.68 km/sec., vn = 4.83 km/sec., for the corresponding S phases. Simply interpreted, these lead to a depth of 36 km. to the Mohorovi
i
discontinuity, including 5 km. of sediments confined to the epicentral region. There is evidence of a phase corresponding to an intermediate layer (the inclusion of which brings the total depth to 39 km.), but the data can also be interpreted to imply a regular increase of velocity with depth in the upper layer, as the presence of a local anomaly.
Footnotes
* Manuscript received for publication December 18, 1950.
The authors were assisted in the work by J. H. Stephen, H. O. Oliver, H. J. Logie, C. P. M. du Plessis, and P. Seligman.
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