part 3] THE ITALIAN EARTHQUAKE OF AUGUST 1895. 231 



10. The Earthquake of 7th August, 1895, in Northern 

 Italy. By Richard Dixon Oldham, F.R.S., F.Gr.S. 



(Read November 8th, 1922.) 



On the 7th of August, 1895, an earthquake was felt over the 

 greater part of Lombardy and Tuscany, and in the Alpine districts 

 of Northern Italy. Although only a feeble shock, nowhere 

 exceeding an intensity of IV Mercalli, it is worthy of attention 

 as being of unusual type, and affording an illustration of some 

 general principles which have been deduced from the comparative 

 study of a large number of earthquakes. The details of obser- 

 vations recorded are published in vol, i. of the ' Bollettino della 

 Societa Sismologica Italiana ' ; on pp. 162-67 reports from 81 

 distinct localities are given, mostly with little more information 

 than a mere record of an earthquake, but a certain number contain 

 fuller details. These localities are plotted on the map accom- 

 panying this paper (p. 232), which also gives an epitome of the 

 pertinent facts recorded. 



The time, as shown by continuous-record seismographs, was 

 about 20h. 50m., mid-European time; the area, over which there 

 is a practically continuous series of records, is approximately 

 triangular, the sides being about 160 miles in length, making the 

 seismic area about 15,000 square miles, and possibly about 20,000, 

 if the shock is included, which was felt, at about the same time, at 

 several places in the Island of Elba. The report, from Portoferraio, 

 is attributed without question to the same earthquake, but it may 

 have been an independent shock, approximately coincident in time 

 with the larger one. In favour of this supposition may be placed 

 the fact that the nearest locality on the mainland from which 

 record was received is over 50 miles from Portoferraio, and that 

 the shock was apparently not sensible, but only instrumentally 

 recorded, at Siena, which is considerably nearer the boundary of 

 the region covered by fairly continuous records. Against the 

 supposition may be placed the fact that the authorities concerned 

 in the preparation of the published accounts, who had the original 

 reports before them, had no hesitation in regarding the reports 

 from Elba as referring to the same earthquake as those from 

 Tuscany. In presence of this doubt, the Elban reports will be left 

 out of consideration : if included, they would only strengthen, and 

 if excluded, would not invalidate, the conclusions illustrated by the 

 other records. 



An attempt was made to determine the degree of intensity, 

 according to the Mercalli scale used in Italy, at each locality ; but 

 in the greater proportion of eases the information was too scanty 

 to allow of this being done. In those cases where a degree could 

 be assigned with some certainty, it is indicated on the map 

 (p. 232). and a consideration of these shows that there was no 



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