SECT. 1] SUB-OCEANIC STRUCTURAL EXPLORATION BY SEISMIC SURFACE WAVES 



123 



Pacific shocks give slightly lower velocities for oceanic Love-wave propagation 

 in certain period ranges. Most of these differences can be ascribed to differences 

 in path. 



From both Love- and Rayleigh-wave observations at Christchurch, New- 

 Zealand, Officer (1955) concluded that the crust of the South Pacific Basin is 

 somewhat thicker than that of the North Pacific Basin by comparison witli 

 the Hawaiian data of Oliver, Ewing and Press. Officer also found the Tasman 



o 



(/) 



E 



o 



> 



Q. 

 O 



5.2 



4.8 

 4.4 

 4.0 

 3.6 

 3.2 

 2.8 

 2.4 

 2.0 



1.6 



1.2 



5.57 km a, = 1-52 km /sec 

 /ii = l.Og/cm-^ 



J. 



77777 



7^/ / / . 



a2 = 7.95 km /sec 



/?2 = 4.56 km/sec 

 Pi = 3.0g/cm3 



-Theoretical curve 



.c.0-^^^ ' O 



?0x ° 



MjA-O 



-n~ 





^^/i- 



—r — 



o 



'0 



A 





Xontinental dispersion 

 (J.T.Wilson) — 



A Honolulu direct 



° Tucson direct 



+ Tucson inverse 



Berkeley direct 



^ Berkeley inverse 



o Palisades direct 



U Palisades inverse 







15 



20 25 



Period (sec) 



30 



35 



Fig. 9. Dispersion oliservations of oceanic Rayleigh waves from tlie Solomon Islands 

 earthquake of 29 July, 19.50, plotted with a theoretical oceanic dispersion curve 

 (Ewing and Press, 1952). Waves over both the direct and antipodal paths were used 

 at Berkeley, Tucson and Palisades, and over the direct path only at Honolulu. 

 Corrections were made for the continental portions of the paths. Within the precision 

 of the experiment no significant difference exists between data for the antipodal path 

 through the Indian and Atlantic Oceans and data for the direct path through the 

 Pacific Ocean. This is indicative of the uniformity of water depth and bottom structure 

 in all of the oceans. 



Basin to have an oceanic crust and found the crustal thickness of New Zealand 

 and the nearby shallow submarine ridges to be about 20 km. Bath and Vogel 

 (1958) found dispersion curves of oceanic character for Love and Rayleigh 

 waves across the Norwegian sea. 



In general, for the deep basins of the Atlantic and Pacific, the higher- 

 velocity Love-w^ave observations are consistent with a basaltic crust about 6 km 



