Dr. C. Davison — The Pendleton Earth-^hake. 173 



The shock occurred at 3.42 a.m., the centre of the disturbed area 

 being ^ mile north of the centre of Pendleton (in lat. 53° 29*6' N., 

 long. 2° 15-8' W.). At this place the intensity of the shock was 7, 

 and not much below 8, for there was some slight damage done,^ 

 several chimney-pots and one chimney-stack being thrown down. 

 On the accompanying map (Fig. 1, which is bounded by the pai'allels 

 of 53° 37' and 53° 23' N. lat. and by the meridians of 2° 4' and 

 2° 29' W. long.) four isoseismals are shown, corresponding to 

 intensities 7 to 4. The isoseismal 7 is 3 miles long, 1|- miles wide, 

 and 4 square miles in area, but, towards the east, the curve may not 

 be quite accurately drawn. The next isoseismal, of intensity 6, is 

 6 miles long, 4^ miles wide, and contains 21 square miles ; the 

 isoseismal 5 is 9^ miles long, 7^ miles wide, and 56 square miles in 

 area ; while the isoseismal 4, which bounds the disturbed area, is 

 15|- miles long, 12 miles wide, and includes an area of 144 square 

 miles. The longer axes of the isoseismal lines are parallel or nearly 

 so, and run from N. 37° W. to S. 37° E. The distances between 

 the isoseismals are approximately the same on both sides of the 

 longer axes. 



The shock was brief in all parts of the disturbed area, the average 

 of 11 estimates of the duration being 2^ seconds. It consisted of 

 a few prominent vibrations, quick-period tremors having been 

 apparently absent. 



The sound-area, which is bounded by the dotted line on the map, 

 is lOf miles long, 8|^ miles wide, and contains 70 square miles. 

 It includes the whole of the isoseismal 5, but falls short of the 

 isoseismal 4 in all directions. The sound was heard by 75 per cent, 

 of the observers. By 14 per cent, of these it was compared to 

 passing traction engines, etc., by 13 per cent, to thunder, by 4 to 

 wind, 9 to loads of stones falling, 31 to the fall of a heavy body, and 

 by 29 per cent, to explosions ; that is, 31 per cent, of the observers 

 refer to types of long, and 69 to types of short, duration. The 

 beginning of the sound preceded that of the shock in 49 per cent, of 

 the records, coincided with it in 24, and followed it in 27, per cent. ; 

 while the end of the sound preceded that of the shock in 13 per cent. 

 of the records, coincided with, it in 16, and followed it in 71, 

 per cent. The duration of the sound was greater than that of the 

 shock in 87, and equal to it in 13, per cent, of the records. 



In the rapid decline of intensity outwards from the epicentre, and 

 in the nature of the sound-phenomena, the Pendleton earth-shake 

 differs widely from other shocks in Great Britain. 



(i) Decline of Intensity. — During the last seventeen years there 

 have been eight British earthquakes of intensity 7 (and nearly 8),. 

 namely, the Inverness earthquakes of 1890 and 1901, the Pembroke 

 earthquakes of 1892 and 1893, the Derby earthquakes of 1903 and 

 1904, the Carnarvon earthquake of 1903, and the Doncaster earth- 

 quake of 1905. In the following Table, the average areas contained 

 by the different isoseismals are contrasted with the corresponding 

 figures for the Pendleton earth-shake : — 



