Page:The origin of continents and oceans - Wegener, tr. Skerl - 1924.djvu/58

of propagation of the surface seismic waves through continents with those through oceanic areas, and found the following values:—

1.—OCEANS.
					Number.
Californian	Earthquake,	April 18, 1906	v. =	3.847±0.045	km./sec.	09
Columbian	Earthquake,„	January 31, 1906		3.806±0.046	km./sec.„	18
Honduras	Earthquake,„	July 1, 1907		3.941±0.022	km./sec.„	20
Nicaraguan	Earthquake,„	December 30, 1907		3.916±0.029	km./sec.„	22
2.—CONTINENTS.
Californian	Earthquake,	April 18, 1906	v. =	3.770±0.104	km./sec.	05
Philippine	Islands, I „	April 18, 1907		3.765±0.045	km./sec.„	30
Philippine„	Islands„II „	April 18, 1907		3.768±0.054	km./sec.„	27
Buchara	Islands, I „	October 21, 1907		3.837±0.065	km./sec.„	19
Buchara„	Islands, I „	October 27, 1907		3.760±0.069	km./sec.„	11

Even if individual results do sometimes overlap, a considerable difference can on the average be recognized to the effect that the velocity of propagation through the oceans is about 0.1 km. per second greater than through the continents. This agrees with the expected theoretical values obtained from the physical properties of volcanic igneous rocks.

On the other hand, Tams also tried to combine the observations of as many earthquakes as possible, and thus obtained from the velocity values of 38 Pacific earthquakes an average value of 3.897 ± 0.028 km./sec., and from 45 Eurasian or American earthquakes 3.801 ± 0.029 km./sec., that is, practically the same values as above.

Angenheister^[1] also has recently examined the seismical difference between ocean basins and continental

Wege,” Centralbl. f. Min. Geol. u. Paläont., 1921, pp. 44–52 and 75–83, 1921.

1. G. Angenheister, “Beobachtungen an pazifischen Beben,” Nachr. d. Kg. Ges. d. Wiss. z. Göttingen, Math.-Phys. Klasse, 1921, pp. 113–146. The work of Omori mentioned in the previous edition, who found such greater differences, rests on a misconception of that author with regard to the nature of the waves and is to be deleted.