224 The N.Z. Journal op Science and Technology. [Nov. 
2. The epicentres of the earthquakes investigated (thirteen world-shaking 
earthquakes, and seventy-seven of character II and III) all lie on the Tonga 
Plateau, on the west side of the Tonga Deep. 
3. The travelling-times for P and S under the Pacific for 6° epicentral 
distance are 13 and 25 seconds smaller than under the European continent. 
This corresponds to a velocity 18 per cent, greater under ocean than under 
continent. 
4. P waves could be followed to A = 145°, the travelling-time for 
this epicentral distance being 1,040 seconds. From the PP curve a part 
was found to split off at about A = 100°, and this part could be followed 
to 177°. 
5. The velocity of the main waves under the Pacific is 21 to 26 per cent, 
greater than under the Asiatic continent. 
6. The absorption of the energy under the Pacific is greater than under 
the Asiatic continent. 
7. The time period of Coda waves travelling under the Pacific is greater 
than that under the Asiatic continent. If follows that, if Coda waves are 
fundamental natural vibrations of the upper crust, the thickness of the 
crust under the Pacific (41 km.) is greater than the thickness under the 
Asiatic continent (28 km.). 
8. The properties of the upper crust deduced from its seismic behaviour 
are in agreement with deductions from gravity observations. 
I have to gratefully acknowledge the assistance of my wife in the 
preparation of this paper, and of Mr. E. Demandt for the preparation of the 
map and figures. 
TABLES. 
Table I. 
Date. 
Time of Origin. 
Epicentre. 
2/1/1907 
H. 
11 
M. 
55 
s. 
40 
21-0° 
S. ; 
175-0° 
W. ; 
Tonga Deep (1). 
31/3/1907 
22 
59 
38 
21-0° 
S. ; 
174-2° 
W. ; 
Tonga Deep (2/ 
31/5/1907 
12 
42 
39 
20-0° 
S. ; 
176-8° 
W.; 
Tonga Deep (3). 
10/4/1909 
5 
27 
3 
18-0° 
S. ; 
174-0° 
W. ; 
Tonga Deep (4). 
26/6/1913 
4 
57 
3 
21-0° 
8. ; 
174-0° 
W. ; 
Tonga Deep (5). 
28/7/1913 
5 
39 
20 
17-5° 
S.; 
74-5° 
W. ; 
Peru. 
6/8/1913 
22 
14 
14 
18-0° 
S. ; 
73-0° 
W. ; 
Peru, 
3/9/1913 
20 
51 
10 
6-5° 
8. ; 
153-5° 
W. ; 
Solomon Islands. 
10/11/1913 
21 
12 
10 
18-0° 
S. ; 
170-0° 
E. ; 
New Hebrides. 
11/4/1914 
16 
29 
30 
160° 
S. ; 
168-0° 
E. ; 
New Hebrides. 
26/5/1914 
14 
22 
40 
0-3° 
8. ; 
138-8° 
E. ; 
New Guinea. 
26/6/1914 
4 
50 
8 
130° 
S. ; 
167-0° 
E. ; 
New Hebrides. 
6/10/1914 
19 
16 
3 
32-5° 
8.; 
182-0° 
W. ; 
Tonga Deep. 
20/12/1914 
14 
8 
43 
16-5° 
8.; 
173-5° 
W. ; 
Tonga Deep (6). 
5/1/1915 
14 
32 
38 
16-5° 
8.; 
168-5° 
E. ; 
New Hebrides. 
6/6/1915 
21 
28 
46 
19-0° 
S. ; 
69-0° 
W. ; 
Chile. 
27/2/1916 
20 
20 
36 
10-5° 
N. ; 
91-0° 
W. ; 
west coast of Central America. 
21/6/1916 
21 
32 
33 
17-0° 
8. ; 
57-0° 
W. ; 
Brazil. 
3/8/1916 
1 
30 
2 
4-0° 
S. ; 
144-5° 
E. ; 
New Guinea. 
11/10/1916 
18 
5 
30 
15-0° 
8. ; 
175-0° 
W. ; 
Tonga Deep (7). 
20/10/1916 
17 
4 
37 
16-0° 
8.; 
173-0° 
W. ; 
Tonga Deep (8). 
1/5/1917 
18 
26 
45 
26-5° 
S. ; 
177-5° 
W. ; 
Tonga Deep (9). 
26/6/1917 
5 
49 
23 
16-0° 
8. ; 
173-0° 
W. ; 
Tonga Deep (10). 
16/11/1917 
3 
19 
28 
29-8° 
S. ; 
178-7° 
W. ; 
Tonga Deep (11). 
30/4/1919 
7 
16 
48 
19-5° 
8.; 
173-0° 
W. ; 
Tonga Deep (12). 
28/10/1914 
0 
16 
20 
37-5° 
8.; 
180-0° 
W. ; 
Tonga Deep. 
