SECTIONAL TRANSACTIONS.—Af. 461 
Dr. Harold Jeffreys and others have shown that the normal depth of an 
earthquake is at the base of the granitic layer, or about 11 miles deep. 
There is no peculiarity in the periodicity of these ‘ shallow ’ focus earth- 
quakes, nor is there any system about the position of their epicentres in the 
earth’s surface. Also when the seismograms for such tremors are examined 
they appear to be perfectly normal, and the L phase is not unduly large. 
At Oxford the epicentres of all earthquakes are determined from the 
S-P differences, using Zéppritz-Turner tables, and a shallow focus earthquake 
is one which calls for a removal of the epicentre so determined away from 
all observing stations, no matter what their azimuth. In other words, if 
the P phase arrives at its correct time, then S appears to arrive late. 
Travel-time graphs have been drawn and calculations made for all the 
readings for all the ‘ shallow ’ focus earthquakes separately, and from these 
it appears that the P wave is quite normal and always well observed, whilst 
the true S by Jeffreys’s tables is practically absent, and the readings usually 
given for S approach more nearly to the Gutenberg PS curve. Several 
seismograms have been examined, and in all these P, PP, PPP,and PS waves 
are discernible, but S and SS are either extremely doubtful or absent 
altogether. 
Conclusions. 
1. The peculiarity of the so-called ‘ shallow ’ focus earthquakes appears 
to be due to the absence or doubtful presence of the true S pulse on all the 
seismograms, though the PS pulse is present and has been usually identified 
as S 
2. Too great praise cannot be bestowed on the work of the International 
Seismological Summary at Oxford, and it seems advisable to continue to 
print all the readings sent by observing stations. 
3. More reliance may be placed on the general identification of the P than 
the S pulse, though it is important to have good tables for P and S separately. 
These are confidently expected when Dr. Jeffreys has completed his present 
work on his new tables. 
4. The fine adjustment of epicentres might with advantage be carried 
out with P readings alone. 
5. Itis advisable to have field evidence with regard to an epicentre wherever 
possible in addition to the evidence of seismograms. 
Rey. J. P. RowLanp, S.J.— The Wensleydale earthquake of 1933, January 14 
(x0.40). 
On January 14, 1933, at about 8.30 a.m. G.M.T., an earthquake shock 
was felt over a large area in the north of England, and was recorded at all 
the British seismological stations, and at a few on the Continent. 
By collation of all the newspaper reports and a few private advices— 
about a hundred reports in all—a seismic map was drawn, which gave 
a series of isoseismals ranging from 7 to 2 on the Rossi-Forel scale, the 
highest enclosing a small area round Upper Wensleydale, and the lowest an 
area of about 25,000 square miles, extending from near Berwick-on-T weed 
to Anglesea, and from the Isle of Man to some distance in the North Sea off 
the Yorkshire coast. The disturbed area is about the average given by 
C. Davison for British earthquakes of central intensity 7. 
Measurement of the P* and S* phases on the seismograms of the three 
nearest observatories, Stonyhurst, Durham, and Bidston, gave the position 
of the epicentre as 54° 20’ N., 2° 18’ W., which is at the head of Wensleydale, 
about one mile to the N.E. of Hawes Junction railway station. Reference 
