1915-16.] The Ochil Earthquakes of the Years 1900-1914. 279 
intensity 2, in the form of a circle with a radius of 35 miles, its area 
would be about 3850 square miles. 
The shock is usually described as a single series of about four prominent 
vibrations, followed, and occasionally preceded, by a tremulous motion. 
It thus only differed from the slighter shocks in possessing more than one 
prominent vibration or thud. As in the earthquake of October 20, 1908, 
a few observers (at Alloa, Blair Drummond, Greenloaning, Logie, and 
Stirling) detected two series of vibrations, the first of which (except at 
Logie) was the stronger, the mean duration of the interval between the 
series being two seconds. The average of thirty-eight estimates of the total 
duration of the shock is 3’0 seconds. 
The sound-area is co-extensive with the disturbed area, but towards 
the boundary there is a marked decline in audibility. While the percen- 
tage of audibility is 92 for the whole area, it is 100 within the isoseismal 
7, 96 between the isoseismals 7 and 5, and 72 between the isoseismals 5 
and 4. The sound is compared to passing waggons, etc., in 20 per cent, 
of the records, thunder in 22, wind in 4, loads of stones falling in 6, a 
heavy body falling in 26, and explosions in 22 per cent. 
