Dispersion of Rayleigh waves produced by nuclear explosions. Crustal structure of western Europe

• Published in: Annals of Geophysics
• Main Author: G. PAYO
• Format: Article in Journal/Newspaper
• Language: English
• Published: Istituto Nazionale di Geofisica e Vulcanologia (INGV) 1964
• Subjects: Meteorology. Climatology; QC851-999; Geophysics. Cosmic physics; QC801-809; Toledo; Novaya Zemlya
• Online Access: https://doi.org/10.4401/ag-5209; https://doaj.org/article/41507eacfa624559ab4dfdb3b68736f3

Most of the nuclear explosion fired near Novaya-Zemlya island from September 1961 to J a n u a r y 1963 (21 in total) have been recorded on the seismographs of Toledo Observatory. The study of these records, mainly concerning the dispersion of Rayleigh waves, has been the purpose of this paper. A crust-mantle s t r u c t u r e for t h e Zemlya-Toledo p a t h has been determined by means of group velocity curves and especially by the phase velocity ones obtained from Rayleigh waves of explosions. This structure supposes a crust of about 40 kms thick with an upper sedimentary layer with a thickness of about 5,5 kms and a shear velocity of 2,3 km/sec. The average shear velocity in the granitic and basaltic layers jointly, is about 3,65 km/sec, permitting a small ambiguity at the position of the Conrad discontinuity between them. A velocity of 4,5 km/sec has been assigned for the underlying crust material, but a better agreement with the data recorded is obtained by taking 0.28 for the Poisson ratio value. Dispersion of Rayleigh waves of these explosions has been compared to the Rayleigh dispersion of some earthquakes of Eurasia, three of them with epicentral distances similar to those of the explosions and other four with the same azimuth in respect to that of Toledo-Zemlya, but more distants. The results do not show any notable difference either in dispersion between explosion and earthquakes or in structure of the path considered. The phase velocity between Toledo and Malaga Observatories supports t h e same above structure for this short path. The velocity of Lg waves, which clearly appears on the record of the explosions, confirms this admitted structure, which serves to deduce t h e more probable transmission mechanism for these channel waves. Also atmospheric pressure waves have been recorded on the three components with very notable amplitudes.