On supposed regional variations in travel times

In two recent papers J. B. Macelwane has expressed the idea that "the difference between the travel-time curves of individual earthquakes of the same focal depth but in different regions may be much greater than the differences between our present average curves" and therefore that "it would follow that all our energies should be concentrated on the intensive study of individual earthquakes." The travel times of P of two Sumatra shocks of 1931 and of a large Solomon Islands shock of that same year, and the travel-time curves of the P waves of the Long Beach earthquake and of the Baffin Bay earthquake, agree within their limits of error with the travel-time curves published by Gutenberg and Richter. Furthermore, the travel-time curves last mentioned agree with the travel-time curves published by Jeffreys and Bullen, in general within one second, and only at distances about 45° is the difference as large as two seconds. As these two sets of curves have been found in quite different ways and by using completely different data, there seems to be no doubt that, at least for large parts of the earth's crust, the travel times of the P waves agree within the limits of error.