Vol. 58.] CARLISLE EARTHQUAKES OF JULY 1901. 3719 
the shock, or of the existence of more than one maximum of 
‘intensity. The mean duration of the shock was 3:4 seconds. 
Sound-phenomena. — The sound, though obviously much 
slighter than that which accompanied the first shock, was heard at 
four places outside the disturbed area—at Linethwaite and Allonby - 
to the west, and Bentpath and Westerkirk to the north-west. This 
overlapping of the sound-area on the west confirms the conclusion 
already arrived at, that the originating fault must hade to the 
-east. 
The sound was heard by 86 per cent. of the observers; and it is 
worthy of notice that the percentage of audibility is the same outside, 
as within, the isoseismal 4 of this earthquake. Comparisons are 
made to passing waggons, etc., in 46 per cent. of the descriptions, 
to thunder in 33, explosions in 17, and to miscellaneous sounds in 
4 per cent. The large percentage of references to the first type is 
no doubt due to the gradually increasing amount of slip from the 
northern and southern margins towards the central region of the 
focus. The sound is uniformly described as faint, with one exception. 
This occurred at Mungrisdale, which is on the minor axis of the 
disturbed area, and about 2 miles from the centre, and here the 
‘sound was evidently loud, for it was compared to terrific thunder. 
Very few observations were made on the time-relations of the 
‘sound and shock. The beginning of the sound either preceded or 
followed that of the shock, while the end of the sound either coin- 
eided with or followed that of the shock, the number of records in 
-each case being three. 
d. July 11th, about 11.10 p.m. 
Number of records 2, from 2 places. 
A slight tremor was observed at Coniston and Mirehouse (near 
Keswick). It is probable that the focus was not far from the 
southern part of that of the first shock. 
Origin of the Earthquakes. 
The principal result to which the investigation of the Carlisle 
earthquakes has led, is the recognition of a deep-seated fault, the 
average direction of which is N. 5° K., and 8. 5° W., and the hade 
throughout is to the east. In the surface-rocks there is no sign 
whatever of such a structure; but the study of two successive 
earthquakes points to the same conclusion, and I do not think that 
the evidence can be interpreted in any other way. 
The movements along the fault which gave rise to these earth- 
quakes were somewhat peculiar. In the first shock, the focus was of 
considerable length, and consisted of two principal portions the centres 
of which were about 23 miles apart, connected by a region wherein 
the slipping was continuous throughout, and much less in amount. 
2p 2 
