218 
The N.Z. Journal of Science and Technology. 
[Nov. 
practically equal epicentral distances, with the path in the former case 
under deep ocean and in the latter case under the Asiatic continent. 
These conditions are especially suitable for an examination of the relative 
speeds of the main phase under ocean and continent, and in fact the results 
show on the average that the waves travelled to Apia in nine minutes less 
time than to Tifhs. 
In the determination of the exact epicentre and time of origin only 
stations with sensitive and quickly recording seismographs were used, and 
a critical examination of the data is given in Table IV, in which the stations 
used are grouped according to azimuth in three groups, Asiatic, Pacific, 
and American. The mean difference between the observed and calculated 
time of arrival for the three groups is in all cases less than, two seconds 
of time— i.e., the epicentral distances from Apia and Tiflis are in both 
cases correct to + 0*5 degree of arc. 
Tables V and VI give the analysis of the seismograms of both quakes, 
the amplitudes and periods being given from wave to wave for the time 
in consideration. In Tables VII and VIII a comparison is given of the 
various phases of the main waves with regard to period, time of arrival, 
travelling-time, and velocity and amplitude in the N.-S. direction and 
vertical. In addition to the observations of Apia and Tiflis figures are 
given for Riverview and Pulkowa for comparison. For Apia the ratio 
of the velocities of the L r waves and L q waves is 0-93, compared with the 
theoretical value 0-92 on the assumption that Poisson’s ratio is = ’25, 
which is the value for a perfect elastic solid. The agreement with theory 
shows that the latter assumption is correct for the earth’s crust— i.e., 
masses under high pressure are nearly perfect elastic solids. 
Velocity V in Kilometres per Second. 
— 
Iv 
L r . 
M x . 
M s . 
m 3 . 
Ocean— 
Apia 
ulV 4 ' 68 
(4-65) 
1 1 4.36 
14-481 
J 4 15! 4-04 
1 3-93 i 
13-75 f d ‘ 4 
2-88 
Riverview 
4-58 
j 3*74 0 „„ 
(3-61 0-67 
3-48 
Continent— 
Tiflis 
(4T6) 007 
O KO O 1 
(3-58) 
' 3*30 | Q.99 
1 3-241 J 
{ms; 3 ' 00 
2-39 
Pulkowa 
4-09 
3-14 
• • 
• • 
V — V 
' ocean • ’ continei 
it 
Apia and Tiflis .. 
1-21 
1-26 
1-25 
1-21 
Riverview and 
1-12 
• . 
1T7 
• • 
• » 
Pulkowa 
From a comparison of the results for Apia and Tiflis given in the 
accompanying table it will be seen that the transverse surface waves (L q ) 
travel 21 per cent, faster under ocean than under continent, while for the 
maximum of the Rayleigh waves the increase of velocity under ocean is 
26 per cent. In Section IV it has already been deduced that the S waves 
(which have practically the same velocity in the upper crust as the L q 
