94 On the Leicester Earthquake of August 4, 1893. 



all parts of the disturbed area ; it was heard after the shock at places 

 near the ends of the minor axis but not of the major axis. This 

 shows, I think, that the preliminary and subsequent sounds must 

 have been due to vibrations proceeding from two distinct origins, 

 situated roughly in a north-west and south-east line. 



Length of the Fault-Slip. On this subject our conclusions are of 

 necessity only approximate. It may be shown, however, that the 

 seismic focus must have been several miles in length. 



The elongated form of the disturbed area and of the isoseismal 

 lines is sufficient evidence of this. If the slip were instantaneous 

 the length of the focus would probably be greater than the difference 

 between the length and breadth of the disturbed area, i.e., than about 

 12 miles. 



Again, the curve which includes all places on the north-west side 

 of the minor axis at which the sound preceded the shock, and all 

 those on the south-east side at which it followed the shock, bounds 

 the area over which the sound-vibrations from the north-west lateral 

 margin were perceptible. Similarly may be obtained the area over 

 which the sound- vibrations from the south-east lateral margin were 

 observed. The centres of these areas must, as a rule, lie vertically 

 over the corresponding lateral margins, and the distance between 

 them must therefore be less than the length of the seismic focus. 

 It is difficult to determine the centre of the north-west area very ex- 

 actly, but the length of the fault-slip, as ascertained by this method, 

 cannot have been much less than 12 or 15 miles. 



It is possible, however, that the slipping did not take place in- 

 stantaneously,* and, if so, these estimates may be a little too great. 

 But, in any case, the fault-slip must have been continued for some 

 distance under the Triassic rocks on which Leicester is situated. 



Nature of the Fault- Slip. The intensity of the shock was greatest 

 on the north-east side of the fault - at and near Woodhouse Eaves, and 

 on the south-west side at Markfield. The line joining these places is 

 perpendicular to the fault-line, and we may therefore conclude that 

 the slip was greatest at this part of the fault. For a distance of two 

 or three milesf in either direction the slip may have been considerable, 

 and it then died out rather rapidly in amount towards the north- 

 west, and much more slowly towards the south-east. That the 

 south-east lateral margin of the seismic focus was longer than the 

 north-west is shown (1) by the relative distances between the iso- 



* The great extension of the isoseismal 4 towards the south-east may be partly due 

 to the fault-slip starting near Woodhouse Eaves and spreading out rapidly in either 

 direction, but towards the south-east with a velocity not much greate'r than that of 

 the earth-wave. 



t The difference between the length and breadth of the isoseismal 5 is about 

 five miles. 



