Open AccessShear waves through the Earth's core
Publication year - 1935
Publication title -
proceedings of the royal society of london. series a, mathematical and physical sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.814
H-Index - 135
eISSN - 2053-9169
pISSN - 0080-4630
DOI - 10.1098/rspa.1935.0049
Subject(s) - inner core , geology , shear (geology) , core (optical fiber) , shear waves , seismology , seismic wave , radius , geophysics , longitudinal wave , earth model , physics , geodesy , wave propagation , optics , petrology , computer security , computer science
Seismological evidence of a central core to the earth was first pointed out by Oldham in 1906. From his analysis of travel-time data regarding longitudinal (P) and transverse (S) waves observed at great distances from earthquake epicentres, he concluded that at a depth equal to about three-fifths of the radius there occurs a transition to material possessing radically different physical properties from that external to this boundary. With the aid of more extensive data assembled by Turner and others, the problem was later re-examined independently by Knott and by Gutenberg. The latte concluded that at a depth of 2900 km the velocity of P waves suddenly decreases from over 13 km per sec to about 8 1/2. The theory involves the appearance of a delayed P wave at epicentral distances beyond 143º, and the chief characteristics predicted for this wave have been amply verified by Gutenberg, by Macelwane and by Lehmann. Also Wadati has lately confirmed the earlier estimates of the core depth from observation on Sc S. Mean density considerations suggest that this core is metallic; and the magnetic properties of the earth are consistent with a nickel-iron composition resembling that found in many meteors.