ON SEISMOLOGICAL INVESTIGATIONS. 257 
The spacing of the isoseismal lines suggests that the focus was decidedly deeper 
than in the case of most of the small shocks felt in the British Isles ; these latter most 
probably originate in the sedimentary rocks. The North Sea earthquake, however, 
is not to be classed among the so-called deep-focus earthquakes, as the appearance 
_ of the records, in which P, is evident, shows that the focus was not below the granitic 
layer. 
New ZEALAND EARTHQUAKE. 
In our last report Prof. Turner drew attention to two severe shocks which had 
occurred, with loss of life, at Wellington, New Zealand. Unfortunately these were 
merely the precursors of a disastrous shock which visited Napier, Hawkes Bay, and 
Wellington at 22 h. 46 m. G.M.T. on February 2. Great loss of life was occasioned, 
and the town of Napier was practically destroyed ; property was seriously damaged 
over a wide area. By coincidence Mr. J. J. Shaw was inspecting a smoked paper 
seismograph at West Bromwich, and saw the record commencing. He watched it 
through, and on noting that the MAX-P difference was the greatest possible, realised 
before the record was complete that the shock was in the vicinity of New Zealand. 
An earthquake which produced even greater disturbances on the seismographs 
of Great Britain occurred on August 10, 1931. The epicentre was near the Great 
_ Altai Mountains in Mongolia. 
British EARTHQUAKES. 
In addition to the North Sea earthquake the following tremors were reported :— 
1. 1931, March 21. Earth tremors were felt in the district of Stoke-on-Trent, and 
these were recorded at West Bromwich at 6 h. 10 m. and 7h. 47 m. G.M.T. 
Houses were rocked, furniture was displaced and crockery rattled, but there 
were no personal injuries or serious damage to property. 
_ 2. 1931, April 14. A disturbance in South Carnarvonshire shortly before noon was 
‘ at the time attributed to earth tremors. Subsequent information has shown 
that it was due to a meteor falling in the district. Information regarding the 
' travel of the meteor and the distribution of the sound waves has been collected 
: by Mr. John R. Owens of Llanrhystyd. 
8. 1931, May 3. An earth tremor occurred in Manchester on the morning of May 3, 
“ 1931; there were no personal injuries, and damage to property was slight. 
_ Mr, A. E. Mourant has published (M.N., R.A.S., Geophys. Suppl, ll, 374) the 
_ results of a detailed study of three earthquakes in the English Channel. The calcula- 
tions follow the method adopted by Jeffreys in discussing the Jersey and Hereford 
earthquakes of 1926. The travel times of P, P*, P,, S, S*, 8,, agree closely with those 
- found by Jeffreys and so confirm his estimates of the thickness of the granitic and 
intermediate layers. Waves are found that are probably propagated in the sedi- 
mentary layer; they are designated P, and §,, as had already been suggested 
_ independently by Mr. E. Tillotson. 
___ The energies of the three earthquakes studied were roughly 5 x 10!7, 10'", 1018 ergs 
 Tespectively. It is suggested that the much lower values of the energy derived from 
_ the Zurich records arise from the scattering of energy by the roots of the Alps. 
¥ 
: ENGLISH CHANNEL EARTHQUAKES. 
: 
ke SEISMOLOGICAL WoRK AT Kew OBSERVATORY, RICHMOND, SURREY. 
__ Microseisms.—The continuous movements known as microseisms are recorded by 
all Sensitive seismographs. The movements are much greater in winter than in 
‘Summer, and appear to be associated in some way with atmospheric storms. The 
ature of the connection is, however, still in doubt. ‘To provide more intimate 
2 owledge of this subject comparisons of microseismic activity at the seismological 
observatories in Great Britain have been undertaken. To initiate this investigation 
the seismograms of one month—January 1930—were examined, and the microseisms 
for four hours daily (1 h., 7 h., 13 h. and 18 h.) were tabulated. 
__ The means of period and amplitude, together with the maximum amplitudes, are 
_ Set out in the following table : 
: 1931 s 
