256 REPORTS ON THE STATE OF SCIENCE, ETC. 
curve (calculated on the basis of a focus near the surface) and the recorded times of 
transit of well-observed earthquakes is excellent. Further, the corrections obtained 
by Prof. Turner and those independently found by Dr. Jeffreys, both from material 
derived from the International Seismological Summary, are in close agreement with 
the Byerly-Jefireys time curve. This depth of 0-04 for the normal focal depth will 
therefore almost certainly have to be abandoned. 
Some Recent SHOCKS. 
By A. W. Lenz, R. SToNELEY, anp F. J. W. WHIPPLE. 
The North Sea Earthquake of 1931, June 7. 
Very early on Sunday, June 7, 1931, at about 1.26 a.m. Summer Time, an earth- 
quake shock was felt in most parts of Great Britain. In Hull and Bridlington the 
movement displaced chimneys and tiles, and there was some panic in the streets. 
In the north of Norfolk most people were awakened and windows rattled viclently. 
In London, on the other hand, but few people woke up; two distinct pulses were 
felt by individuals who had not retired for the night. The shock was felt in the 
Channel Islands, in the north of France, in Belgium, Holland and Denmark, and in 
Germany at places as far away as Hamburg and Brunswick. As far as is known no 
earthquake has.ever been felt over such a large area in the neighbourhood of the 
British Isles. 
The records of the earthquake are being studied by Dr. H. C. Versey and Mr. ~ 
R. Stoneley, of Leeds University, who would be glad to receive reports of personal — 
experiences. A seismic map has been prepared from about 400 observations, and on 
this the isoseismal lines are well defined. The boundary of the area in which the © 
strength was 4 or greater on the Rossi-Forel scale (i.e. movable objects shaken, windows 
rattled) passes approximately across Somerset, the Irish Sea, and northwards across 
Scotland to Banfishire. Isoseismal 5 (shock felt by most people, large objects shaken) 
crosses the Firth of Forth, Morecambe Bay, and. across the Midlands to Harwich. 
The line of isoseismal 6 (most sleepers awakened, with some people rushing in terror 
out of houses) was from the mouth of the Tees, through Yorkshire, passing to the 
east of Leeds and meeting the coast again near Yarmouth. There is a small area 
round Hull, Bridlington and Filey in which damage was done to houses (strength 7). 
The shock was felt as far west as Waterford in Ireland. 
Excellent seismographic records of the earthquake were obtained at all the eight 
British stations as well as at numerous stations on the Continent. Disturbances 
were also detected at a few stations in the United States. ; 
The interval between the P and S phases on the seismograms at Kew Observatory 
was 30 sec., corresponding to an epicentral distance of 270 km., and the bearing 
(obtained by comparison of the north and east components of P and P,) was estimated 
as 22°+2°. These data imply an epicentre with co-ordinates 53-8° N., 1:2° Ee By 
comparison of the times of arrival of the first pulse at certain stations Father Rowland 
found the co-ordinates 53° 57’ N., 1° 25’ E. Mr. Stoneley, using the data from 
twenty-five stations, finds that the known velocity of transmission of P to distances 
less than 1,000 km. (7:77 km./sec.) gives close accordance between the calculated 
times and the observed times of arrival of P, provided Father Rowland’s epicentre 
is used. This epicentre therefore cannot be greatly in error, and it is interesting to 
note that for a near earthquake an accurate epicentre can be obtained from the times 
of arrival of P alone. The epicentre indicated by the seismic map agrees closely 
with that obtained by Father Rowland. : 
The epicentre was under the North Sea near to the Dogger Bank, and abou 
60 miles from the coasts of Yorkshire and Norfolk. There is no record of any previou' 
earthquake with this epicentre. The last considerable earthquake under the Nort 
Sea was on January 24, 1927, about 400 miles away and close to the coast of Norway. 
This earthquake was felt in Scotland and the east of England. + 
The shock was felt on several ships in the vicinity. The navigator of a motor 
boat, about 25 miles S.E. of Flamborough Head, reported that a sound like that 
a distant lightship gun was first heard; followed by a series of underwater explosio 
like those of depth charges four to six miles away. The sea was then calm, but 
fifteen or twenty minutes later a heavy swell developed, and became very confused 
appearing to roll from all directions. 
