Dr. C. Davison — The Stafford Earthquakes of 1916. 311 



distance between the foci is 6 or 7 miles, and the direction of 

 the longer axis of. the isoseismal 6 is N. 31° E. Eight hours later, 

 on the same day, the earthquake was followed by an interlocal 

 after-shock, the direction of the longer axis of the isoseismal 4 being 

 K 27° E. Lastly, on August 27, 1906, l a much slighter twin- 

 earthquake occurred in the same foci as the earthquake of 1904, the 

 direction of the longer axis of the isoseismal 5 being jS". 25° E. 

 The mean direction of the earthquake fault is thus about N. 28° E., 

 which is nearly, but not quite, at right angles to that of the 

 Stafford earthquake fault. 



Again, on August 4, 1893, 2 a twin-earthquake of intensity 5 

 occurred in Leicestershire. The principal epicentre lies 2 miles 

 S.S.W. of Loughborough, and the direction of the longer axis of 

 the isoseismal 5 (which surrounds this epicentre only) is E. 30° S. 

 The second epicentre lies close to the village of Tugby, and is 

 17 miles E. 34° S. of the other. There can be little doubt 

 that both impulses originated along a single fault, the direction of 

 which at the north-west end is E. 30° S., and at the south-east end 

 about E. 40° S. A later earthquake, which occurred on June 21, 

 1904, in the south-eastern focus only, shows that the direction of 

 the fault there is E. 42° S. 



Now, if the fault-lines of the Stafford and Derby earthquakes be 

 produced to meet, their point of intersection is 9 miles from the 

 eastern focus of the Stafford earthquake and 18 miles from 

 the southern focus of the Derby earthquakes. In both earthquakes, 

 the distance between the foci is 8 or 9 miles, which is therefore 

 the distance between the crest and trough of a crust-fold. Thus, 

 the point of intersection of the two fault-lines is at a distance of 

 half a crust-fold-length from the nearer focus of the Stafford 

 earthquake, and of a whole crust-fold-length from the nearer focus 

 of the Derby earthquakes. Also, if the fault-lines of the Derby 

 earthquakes and of the Leicester earthquake of 1893 be produced 

 to meet, their point of intersection is about 10 miles from the other 

 point of intersection, about 8 miles from the southern focus of 

 the Derby earthquakes (that is, about half a crust-fold-length from 

 either), and about 26 miles from the north-western focus of the 

 Leicester earthquake and 43 miles from its south-eastern focus 

 (that is, about three and five half crust-fold-lengths from the 

 two foci). 3 



If we may assume that the earthquake-faults are at right angles 

 to the folds, to the growth of which the earthquakes are due, it 

 would seem that the crust at a depth of a few miles below the 

 counties of Stafford, Derby, and Leicester, is corrugated in two 

 systems of folds approximately at right angles, and that the axes 

 of the north-and-south folds exhibit a fan-shaped arrangement or 



1 Geol. Mag., Vol. V, pp. 301-3, 1908. 



2 Quart. Journ. Geol. Soc, vol. lxi, pp. 1-7, 1905. 



3 It will be noticed that the distance between the foci of the Leicester 

 earthquake is about double that between the foci of the Derby and Stafford 

 earthquakes. Possibly, the foci of the Leicester earthquake occupy the crests 

 of successive folds ; but there are difficulties in the way of such an explanation. 



