Open AccessTHE TIMES OF P UP TO 30°
Author(s) -
Jeffreys Harold
Publication year - 1952
Publication title -
geophysical journal international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0956-540X
DOI - 10.1111/j.1365-246x.1952.tb03023.x
Subject(s) - curvature , azimuth , geology , geodesy , seismology , interval (graph theory) , geometry , mathematics , combinatorics
Summary Times of P in Mediterranean, Japanese and Californian earthquakes are analysed with the objects of testing the generality of the increase of the velocity at short distances found in Europe and the evidence for Gutenberg's layer of low velocity. The Mediterranean earthquakes do confirm the increase at short distances, but the Japanese ones agree with the tables in use, and there is clear evidence of a regional difference. The evidence from North American earthquakes is conflicting. It does not definitely indicate any change from the present travel times, but the uncertainties are larger than in the other regions, chiefly because there are rarely enough stations in approximately the same azimuth and at greatly different distances to give much information. The difference of the times at 2° and 25° is about the same in Europe and Japan, but in comparison with them the times in Europe at 8° are about 3° earlier. The time‐curve in Europe is nearly liner up to 14°. There is evidence in both regions for a strong curvature of the time‐curve between 15° and 20°, but it does not decide whether dt/d Δ is continuous or discontinuous in this interval. The curvature of the time‐curve is in any case surprisingly small, because laboratory studies of the variation of elastic moduli with pressure indicate an increase of velocity with depth several times that given by any set of travel times. Increase of temperature with depth would presumably reduce the rate of increase but does not appear sufficient to account for the discrepancy.