386 L. MARTIN ALASKAN EARTHQUAKES OF 1899 



Africa 



Place. 



Type of seismo- 

 graph. 



Described by 



Published in 



Mauritius, Indian 



Milne 



Seismological 

 Committee. 



Seismological 

 Committee. 



Circular 1, B. A. A. S., 



Ocean. 

 Cape Town, South 

 Africa. 



Milne 



1900, p. 17. 

 Circular 1, B. A. A. S., 





1900, p. 22. 



Times of Yakutat Bay Earthquakes 

 determined from 8eismooram8 



Dr. D. W. Oldham has computed the time of origin of the three largest 

 Yakutat Bay earthquakes^^ from the distant seismograph records. These 

 times he determined, with an error of not more than one minute of time, 

 by the use of curves first produced in his paper, "The propagation of 

 earthquake motion to great distances."^^^ 



In a personal communication, which he has kindly alloAved me to use, 

 he states that in this computation he used 



"the records of the Italian seismographs and adopted this course for two 

 reasons ; that, as shown in the paper referred to, the heavily weighted pendula 

 with mechanical record give much more concordant results for the first two 

 phases than light pendula with a slow-moving photographic record, and, 2d, 

 because the curves having been deduced from the records of instruments of 

 the type used in Italy, it is logical to use the data obtained from instruments 

 of this type in applying them to obtain the time of orighi of an earthquake. 



"In the case of the Alaskan earthquakes the Italian observatories are dis- 

 tant from 78 degrees, in the case of Padua, to 81 degrees in the case of 

 Catania. The mean time interval, as deduced from tbe curves, is consequently 

 about 13.5 minutes for the first and 28.5 minutes for the second phase. I have 

 consequently extracted from the published accounts the times of commence- 

 ment, and, where recorded, of the first marked increase of movement, repre- 

 senting the second phase ; these are tabulated below and the resulting time of 

 origin deduced. The times so obtained are doubtless subject to a slight error, 

 but this probably does not exceed one minute of time — an error which becomes 

 insignificant when dealing with the comparatively slow traveling waves of the 

 third phase. (The times tabulated here have been obtained, in the case of 

 Padua, directly from the diagrams obtained there, which Professor Vicentini 

 very kindly allowed me to examine; in the case of the observatory at Quarto 

 (Florence), from the publications of that observatory, and in the case of the 

 other Italian observatories, from the details published in part ii of the Bolle- 

 tino della Societa Sismologica Italiana.) 



8» Quarterly .Tom-nal of the Geological Society, vol. Ixii, 1906, p. 459. 

 100 Philosophical Transactions of the Royal Society of London, series A, vol. 194, 

 1900, pp. 35-74. 



