Dr. C. Davison— The Stafford Earthquakes of 1916. 303 



Pkinctpal Earthquake of January 14, 1916. 



Time of occurrence, 7.29 p.m. ; intensity, 7 ; centre of isoseismal 

 7 iu lat. 52° 52' N., long 2° 9' W. ; number of records, 1241, from 

 580 places. 



Time of Occurrence. 



The time of occurrence is determined with unusual precision. 

 The first tremors were recorded at West Bromwich, as Mr. J. J. 

 Shaw kindly informs me, at 7h. 29 m. 6 s. p.m. At Birmingham 

 I felt the "shock at 7 h. 29im. The average of seventy -four 

 estimates of the time, which, according to their observers, are. 

 accurate to the nearest minute, is 7 h. 29 m. As these observers 

 were all within the isoseismal 4, it is probable that the time at 

 the epicentre must have been 7.29 p.m., -or possibly a few seconds 

 earlier. 



Isoseismal Lines and Disturbed Area. 



On the map of the earthquake (Fig. 1) are shown five isoseismal 

 lines corresponding to intensities 7-3 of the Rossi-Forel scale, or 

 rather of that form of the scale which I have employed in studying 

 British earthquakes, 1 the two inner isoseismals being represented on 

 a larger scale in Fig. 2. With regard to all the isoseismal lines, 

 except the innermost, it should be mentioned that the comparative 

 scarcity of observations in the western district does not admit of 

 great accuracy in tracing the lines there. The true course of each 

 line may vary by a mile or more, and in the outermost line by 

 several miles, from that laid down on the map. The inaccuracy, if 

 it exists, is not, however, of much consequence. 



The dimensions of the isoseismal lines are given in the following 

 table : — 



The centre of the isoseismal 7 is in lat. 52° 52' N., long 2° 9' W.„ 

 or 2 miles S.S.W. of Stone. The distances between the isoseismals 

 7 and 6, 6 and 5, 5 and 4, are respectively 9£, 18, and 32 miles on 

 the north side, and 5, 12-§-, and 12 miles on the south side. 



Outside the isoseismal 3, the shock was probably felt at Maryport, 

 14 miles from the line. Excluding this exceptional observation, the 

 area disturbed by the earthquake is about 50,200 square miles. 



If we measure the relative strength of British earthquakes by the 

 area enclosed within the isoseismal 4 — for the isoseismal 3 cannot 

 always be drawn — the Stafford earthquake occupies the seventh 



1 Geogr. Joum., vol. xlvi, pp. 360-1, 1915. 



