582 



KNOWLEDGE & SCIENTIFIC NEWS. 



[November, 1906. 



Earthquakes.' 



Bv Camillf. Flammarion. 



The aianninsj eruption of \'esiivuis was hardly over 

 than the world was aghast at the earthquake of San 

 Francisco. The Italian volcanic eruption lasted from 

 the sth to the T2th April; and the North American 

 earthquake hegan, at 5-13 on April i8, with a violent 

 trembling of the carih in vertical, horizontal, and 

 oblique oscillations, and. as we know, it caused the 

 overthrow in tlie course of two or three minutes of the 

 greater part of the " Queen of the Pacific," and it was 

 followed by an immense fire. Four hundred deaths 

 were the consequence, and the financial loss was com- 

 puted at four hundred millions of dollars. This 

 disastrous shock was followed by several others, 

 notablv that of the 20th April, and the 19th May. 



California has always been subject to earthquakes. 

 In a list of the seismic disturbances in California, Pro- 

 fessor Holden reports as many as 514 in the whole 

 State, 254 being in the territory of San Francisco 

 alone, and this only from 1850 to 1886. During the 

 nineteenth century there have been ten serious shocks, 

 and in 1868 a part of the town was destroyed. 



The towns and villages on the zone of maximum of 

 intensitv were cruelly affected for the length of 180 

 miles (290 kilometres), from Santa Rosa to Salinas. 



The last eruption of \'esuvius and the earthquake 

 of San Francisco, following the earthquake of Calabria, 

 which continued from the 8th to the i;th September 

 last, the one in India on the 4th .\pril. so replete with 

 terrible consequences, and the many slight shocks ob- 

 served everywhere, lead us to study these phenomena 

 of nature by the help of the most recent investigations 

 of science. The planet which we inhabit does not possess 

 the apparent stability which it presents to the mind 

 uninstructed by history and science. The intensitv of 

 seismic shocks and the elasticity of the terrestrial globe 

 was seen in the great disaster of .Assam. This earth- 

 quake, which was not less disastrous than that at 

 Lisbon in 175^. took place on the 12th Ume, 1897, and 

 the tremors of the earth not only spread from this spot 

 to the antipodes, but they were registered again on the 

 seismographical apparatus of India, after having twice 

 made the tour of the globe, like the atmospherical and 

 marine waves caused by the gigantic explosion of 

 Krakatoa in 1883, w'hich I showed in my special work 

 on the subject. 



The earthquake at .San Francisco seems to have been 

 of the same intensity and energy as those of Lisbon 

 and -Assam. It was registered by all the seismometers 

 of the globe, and it was not till thev had twice made 

 the tour of the world that the tremors decrea.sed in 

 force. I have before me the diagrams of the oscilla- 

 tions in England (Birmingham'). Beleium (the Royal 

 Observatory of LVcle), .Austria (Laibach, etc.), and 

 they show the course of this wave. It passed Birming- 

 ham at 1.25, by Greenwich time. .As the time of 5.13 

 at San Francisco corresponds to that of 1.13 at Bir- 

 mingham, we see that it only took twelve minutes 

 to go from San Francisco to Birmingham. It arrived 

 at the same time at Brussels (L'CCJe). and a little later 

 in Austria, where the apparatus registered an oscilla- 

 tion lasting from 2.30 to 3.30. Tlie time of Central 

 Europe is in advance of Greenwich time. Mr. Davison's 



* Tran-^lated by Rachel ChalUce (Member'of the Astronomical 

 Society of France). 



study of the oscillations of Birmingham showed that a 

 second registration followed the first in 3 hours 13 

 minutes, after having made ike four oj the ivhnle world. 



If to the 40,000 kilometres, which represent the tour 

 of the world, we add the 9.000 kilometres which 

 separate Birmingham from .San Francisco, we .see that 

 the first impulsion was powerful enough to cause a 

 vibration which resounded at least to the distance of 

 50,000 kilometres. 



The vibrations produced by the earthquakes are 

 transmitted at a different rate of speed through the 

 entire mass of our planet to that with which they pass 

 along the external crust. 



On the 2nd February, the .seismometer of the Ob- 

 servatory of Florence registered a disturbance 9,000 

 kilometres off; and on that day a submarine volcanic 

 eruption and a tidal w-ave destroyed the town of 

 Buenoventura, a port of Columbia, on the Pacific 

 Coast. I also stated, on the 7th March, that the 

 central meteorological bureau of \'ienna, in .Austria, 

 registered on the night of the i8th-ioth February, an 

 earthquake 12.000 kilometres off, which proved to be 

 the violent shocks at Martinique, Saint Domingo, 

 Saint Lucie, and a part of the Antilles, and the re- 

 crudescent activity of the mountains of Peleus. 



The shocks at San Francisco were remarkable for 

 their length and their rotary character. The violent 

 phase lasted forty seconds, but it was three minutes 

 and a-half before their registration was concluded by 

 the apparatus of the Xaval Observatory of Mare Island. 

 Before their destruction, it was noticed that many 

 houses had left the straight line. A whole street rose 

 up like a wave several metres long. In Calabria and 

 elsewhere, deep, open crevices were made by these 

 dislocations. 



Earthquakes vary as much in the distance of their 

 effect as in the intensity. Some, like those of Lisbon 

 in 1755. or .Assam in 1892, are felt two or three million 

 square kilometres away, and others do not vibrate 

 further than a hundred or ten square kilometres. In 

 1879, the inhabitants of Linthal, in Claris, were thrown 

 out of their beds, whilst fifteen kilometres from there 

 nobody felt it. It has been generally supposed that 

 earthquakes are the consequence of volcanic eruptions. 

 This idea is evidently erroneous, and nowhere is it 

 more proved to be wrong than in Japan. 



Everybody knows that Japan is far excellence the 

 land for earthquakes, as it has as many as three or 

 four a dav. But the most unstable regions are not by 

 any means those contiguous to Fusiyama, the great 

 Japanese volcanic mountain, which, moreover, has been 

 quiet for the last three hundred years. No eruptive 

 manifestation accompanied the great .seismic dis- 

 turbances of 1 891 and 1897, but many earthquakes have 

 taken place in regions not at all volcanic. .At San 

 Francisco, for example, there is no volcano; and there 

 have been earthquakes in many other spots where the 

 volcano is absent or where, if it exists, it has shown no 

 activity. .Seismic disturbances are not caused by vol- 

 canic eruptions, either near or distant. But the seismic 

 disturbances and volcanic eruptions are both due to 

 the pliant state of some region of the earth's crust. 



Seismic disturbances are always in the neighbour- 

 hood of moimtains. The most prolific regions are those 

 of a sleep decline. The regions of a slight decline are 

 those which, at 200 kilometres from the sea. have only 

 a slope of from five or ten degrees; and places where, 

 at the same distance from the .seashore, there is a 

 steep descent exceeding three degrees. .All the regions 

 which are incontestablv seismic have a fall of three 



