﻿Vol. 6 1.] LEICESTER EAKTHQTJAKE3 OF 1893 AND 1904. 7 



The faults of Charnwood Forest have been mapped by Prof. 

 Watts, F.R.S., 1 to whom I am indebted for information on the geo- 

 logical structure of the district. In PL I, the more important 

 strike-faults are reproduced from Prof. Watts's map, the transverse 

 faults of later date being omitted, for the sake of simplicity. The 

 faults on the north-east side of the Charnwood anticlinal axis 

 probably hade to the north-east, and those on the south-west side 

 in the opposite direction. In PI. I, the former are indicated by 

 broken lines, and the latter by dotted lines. 



The fault which satisfies the seismic conditions most closely is 

 that marked A in PI. I. Its mean direction in the neighbourhood 

 of Woodhouse Eaves is W. 27° N. and E. 27° S., it hades in all 

 probability to the north-east, and it passes about 2 miles to the 

 south-west of the centre of the isoseismal 5. Owing to the covering 

 of Triassic rocks, it cannot be traced farther to the south-east than 

 the village of Cropston ; but there is no reason for supposing that 

 it dies out at that point. Assuming, then, that the fault referred 

 to extends to the neighbourhood of Tugby, trending there more 

 nearly in a south-easterly direction, I will now trace briefly the 

 history of the recent movements. 



In 1893, the displacements in the two foci took place almost 

 simultaneously and apparently in opposite directions, the interfocal 

 region remaining stationary or nearly so. The centres of the foci 

 were about 17 miles apart ; and it is clear, from the more rapid 

 decline in intensity from the north-western epicentre, that the 

 corresponding focus was situated at a less depth than the other. 



One effect of the double slip was to cause an increase of stress in 

 the regions of the fault-surface bordering the margins of both foci, 

 the greatest accession of effective stress being experienced by the 

 interfocal portion of the fault. It is probable that the earlier slip in 

 1904 took place in or near the south-eastern margin of the north- 

 western focus of 1893 ; but it may have been caused by a small slip 

 along one of the faults marked B & C in PI. I. Two hours later, 

 this was followed by a double (not a twin) slip in or near the 

 north-western margin of the south-eastern focus ; and, judging from 

 the rapid decline in the intensity of the shock, at a less depth than 

 either of the foci of 1893. The second part of this double slip 

 showed a farther migration (of 2 or 3 miles) towards the north- 

 west, and a still closer approach to the surface of the earth. 



EXPLANATION OF PLATE I. 



Map illustrating the area affected by the Leicester earthquake of August 4th, 

 1893, on the approximate scale of 8 miles to the inch. 



Proc. Geol. Assoc, vol. xvii (1902) pi. xix. 

 [For the Discussion, see p. 33.] 



