182 
ME. J. H. JEANS ON THE VIBRATIONS AND 
Evidence from the Distrihution of EarthquaJce Centres. 
§ 38. Tt call ])e seen that the earthquake regions of the world have a reference, as 
regards theii- distriliution on the earth's surface, to this pear-.shaped figure, and this, 
again, must he considered as evidence. 
Let us first examine the facts. Milne divides the eartlupiake-areas of the globe 
into twelve distinct regions, and a map of these is given in the ‘ British Association 
Beport’ for 1902."' These regions are given in the following table. The first figure 
denotes the numhei- of large earthquakes which have occurred in these regions in the 
three yeais 1899-1901. The earthquakes from the three regions printed in italics 
wei-e small in comparison with the others. In the last column is given the 
approximate latitude of the centre of each region, referred to Cfreenwich as pole (the 
latitude of rireenwicli being taken to he + 90°). 
1 ABLE of Earth(|uake Begions. 
A 
25 
Alaskan 
+ 10 
(4 
17 
-Mauritian 
+ 10 
B 
14 
Coi'flillerean 
(J 
H 
d ) 
•V./A AfJaniic 
+ 1 o 
C 
16 
Antillean 
+ 25 
I 
.> 
T} 
A'.//'. „ 
+ 6M 
D 
12 
Andean 
0 
J 
-V. 
+ 70 
E 
29 
Japanese 
- 5 
K 
14 
Asiatic 
+ 45 
F 
41 
Javan 
-25 
B 
0 
Antarctic 
[small] 
Now, it will be at once noticed that for most of these regions the latitude is small. 
If we weight the regions according to the corresponding number of earthquakes, 
giving half-weight to the small earthquakes in regions H, I, J, we find as the mean 
of the numei ical values of the latitude about 20°, whereas if the regions were 
distributed at random we slioiild expect the mean latitude to be (^tt — l) radians, or 
about 33°. We therefore see that the eartlupiake regions tend to lie near the 
equator of our pear. Tlie evidence can be put in a more striking way as follows :_ 
Exactly half of tlie surface of the globe is of a latitude less than 30°. The half for 
vhich the latitude is less tlian 30 , measiirefl fi'om CTreenwich as pole, was responsible 
for 150 earthquakes; the remaining half vms responsible only for 42, of which 28 
were the small earthquakes from regions H, I, J. There is, tlierefore, no doubt that 
the princfctl earthf|uakes tend to emanate from points near to the equator of the 
supposed pear. 
Now, if we look back to fiu. i, 
quakes occur where the “slope” 
is the same as that to which 
we see tliat this is equivalent to saying that earth- 
in the figure of the earth is steepest. This conclusion 
the British Association Committee were led from a 
p. 4. 
Brit. A.'^soc., / 2tid Report, Belfast, 1902, “ Seismological Investigations,” 
