258 REPORTS ON THE STATE OF SCIENCE, ETC. 
Microseisms, Great Britain, January 1930. 
| Type of re Mean Mean Max. 
Observatory. | Seismo- ie period.| Amp. Amp. 
| graph. | PEE? dete U v. 
| Dyce (Aberdeen) . | Milne-Shaw N—S 6-4 2-9 10-8 
Edinburgh . “al us E—W 6-4 55 16-6 
Durham proves owt 6| 3 N=S | 61 3:3 10-7 
Stonyhurst F ‘ oe 8 | E—W 6-3 3:7 1aeZ 
Liverpool . ‘ é : “s N—S 6-3 4-6 16-0 
| Oxford : : : . zi N—S 6-5 4-8 16-8 
95 i : 5 : oi E—W . 655 2-9 9-7 
paikew See ony P yittfoodahh sive) erGalitzin’ 1MN=2S 6-7 2-3 7-2 
pad 3 : é : 45 E—W 6-8 2:5 9-4 
hele é : i rl Ff: Z 6-7 2:7 10-2 
What geographical, geological or instrumental causes can account for the large 
differences between the characters of the microseisms at different places, is a mystery. 
It is held by some seismologists that microseisms are generated when sea waves 
break against the coast, whilst others believe that the oscillations of the ground are 
due to wave motion of the sea causing variations in pressure on the sea bed. - 
The outstanding feature of the tabulation of microseismic activity at British 
stations during January 1930 is a rapid increase in activity on the 11th and a rapid 
fall on the 12th, the maximum amplitudes being in every case about three times the 
average. A deep depression was centred between Scotland and Iceland at the time, 
and an intense secondary travelling rapidly from the west crossed England during 
the afternoon of the 12th. Neither on the Atlantic coast of the British Isles, nor 
round the North Sea, nor on the coasts of Norway or Iceland, nor round the Bay of 
Biscay, was there a conspicuous maximum of sea disturbance or of wind force during 
the night when the microseisms were so much exaggerated. As far as can be seen 
the observations give no support to either of the current theories. 
THe Focat DreprH or EARTHQUAKES. 
An innovation in practical seismology was made on February 20, 1931, when 
Mr. F. J. Scrase, who had been studying the characteristics of the seismograms of 
earthquakes with abnormal focal depth, saw that a disturbance recorded at Kew 
Observatory was of this nature, and was able to announce that the focal depth of 
the earthquake, which had an epicentre near the Sea of Japan, was probably about 
250 miles. The records of this disturbance are being collected at Kew, and a detailed 
investigation of the phases is in progress. 
An account of the research on earthquakes with deep foci appeared in the 
Proceedings of the Royal Society, A, Vol. cxxxii., 1931. The following papers of 
seismological interest have also been published : 
F. A. Bellamy and E. F. Bellamy. Herbert Hall Turner : A Notice of his Seismological 
Work. County Press, Newport, [.0.W. 
H, Jeffreys. The Revision of Seismological Tables. Monthly Notices. Geo. Supp., 
January 1931. 
A. E. Mourant. Earthquakes of the Channel Islands Neighbouring Countries. 
Société Jersiase, 1931. 
F. J. Scrase. Two notes on the Operation of Galitzin Seismographs. Meteorological 
Office Geophysical Memoirs, V. 49, 1930. 
F. J. Serase. The Instrumental Phase-difference of Seismograph Records: an 
Illustration of the Properties of Damped Oscillatory Systems. Proc. Phys. Soc., 
Vol. xliii. 3, No. 238, 1931. 
R. Stoneley. Some near Harthquakes reported in the International Seismological 
Summary. Monthly Notices. Geo. Supp., January 1931. 
R, Stoneley. On Deep-focus Earthquakes. Gerlands Beitrdge zur Geophysik, 
Vol. xxix. (1931), pp. 417-435. 
F. J. W. Whipple and A. W. Lee. Studies in Microseisms: (a) The Question of 
Diurnal Variation; (b) The Variation of Amplitude with Period. Monthly 
Notices R.A.S., Geophys. Supp., January 1931. 
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