733 



EARTHQUAKES. 



EARTHQUAKES. 



731 



EARTHQUAKES are the most terrific of all natural phenomena 

 The solid surface of the globe is put in motion by them, and assumes 

 an appearance which in some cases may be compared with the sea when 

 agitated by the wind. 



The least dangerous of these phenomena are those which by the 

 Creoles of South America are called Tremblwes, a term which may be 

 translated by tremors. The surface of the earth is put in a trembling 

 motion, by which such objects as are not well supported are thrown to 

 the ground, and even walls are split, but the damage does not extend 

 farther. Life is safe, and property but slightly injured. These 

 tremors are by far the most common kind of earthquakes, and occur in 

 some countries of South America, especially in Chile, almost every 

 day, at least in certain seasons. 



The ttrremotos of the Creoles, or proper earthquakes, give to the 

 surface either horizontal oscillations, not dissimilar to the waves of an 

 agitated sea, or they consist in violent perpendicular upliftings, so that 

 it would seem as if repeated explosions were exerting their force against 

 the roof of a subterraneous cavern, threatening to burst it open and to 

 blow into the air everything placed over it. By these earthquakes 

 walls are overthrown, and fissures are produced in the ground. The 

 latter are frequently more than a foot in width, and sometimes water 

 gushes out of them like a fountain. 



Nothing makes such an awful impression on the senses as an earth- 

 quake. The earth is violently convulsed, heaving up and down in a 

 manner hardly conceivable by those who have not witnessed it. The 

 tottering buildings, the falling of the tiles, and the crashing of the 

 timber* of the roofs, completely distract the senses. Fear drives men 

 from their houses ; but they do not always find safety out of doors. 

 No person can stand without support : people cling to one another, to 

 trees, or to posts. Some throw themselves on the ground ; but the 

 motion of the earth is so violent that they are obliged to stretch out 

 their arms on each side to prevent themselves from being tossed over. 

 Animals are equally alarmed. They stand with their legs spread out 

 and then- heads down, trembling violently. The air itself seems to 

 participate in the convulsion, for the birds fly about wildly. Mean- 

 while the sea retires from the shore ; but after a few minutes it re- 

 turns in a high wave, which advances like a watery wall with incredible 

 velocity, and covers all those tracts which are not more than fifty feet 

 above high-water mark. It rushes back with equal velocity. This 

 motion of the sea is repeated as long as the shocks of the earthquake 

 are violent. Vessels sailing along a coast convulsed by an earthquake 

 feel also a motion quite different from that produced by gales or 

 currents. The loss of life by earthquakes is sometimes considerable. 

 It is chiefly produced by the falling of the buildings when the shock is 

 so unexpected that the inhabitants have not time to escape. In some 

 cases the overflowing of the sea has been fatal to a great number of 

 persons. People have also been swallowed up by the fissures caused 

 by earthquakes. 



Earthquakes are generally preceded and dome times attended by a 

 subterraneous noise, which is compared by some to that of a very 

 heavy artillery waggon rolling quickly over a stone pavement at a dis- 

 tance ; by others, to the echo of distant thunder in a mountainous 

 country. It is worthy of remark that this noise is sometimes heard 

 without any earthquake taking place, as in 1784, at Guanaxuato, in 

 Mexico, and that it has been as audible in places situated at a con- 

 siderable distance from the seat of the earthquake as in those which 

 experienced the shocks. There are also many cases on record in 

 which the earthquakes have not been attended by such subterraneous 

 noise. 



The single shocks of an earthquake last from a few seconds to two or 

 three minutes. Sometimes they follow one another at short intervals. 

 It is remarkable that generally either the first or one of the first shocks 

 is the moat violent, and that they afterwards gradually decrease in 

 force. Sometimes they return for several days, and even weeks; 

 and in some places, as at Copiapo, in Chile, they are of daily 

 occurrence. 



Earthquakes are sometimes experienced over an immense tract of 

 country. The great earthquake in Chile (in 1835) was felt at all places 

 between the Island of Chiloe (40 S. lat.) and Copiapo (27 S. lat.) : 

 consequently over 13 of latitude. It extended from the island of 

 Juan Fernandez to the town of Mendoza, on the east side of the range 

 of the Andes, over 10" of longitude. But when earthquakes extend 

 over such an immense tract of country, some districts are always 

 convulsed with greater violence, and these may be considered as 

 tin- i:i:ntre of the earthquake. The farther a place is removed from 

 these centres, the less violent, as a general rule, are the shocks. 



We know little, or rather nothing, of the origin or cause of earth- 

 quakes. It may, however, be considered as certain that they are due 

 to the same agency which produces volcanic eruptions. These 

 eruptions are frequently preceded by earthquakes ; and whenever, in 

 places situated near active volcanoes, it is observed that no smoke 

 issues from their craters, the inhabitants begin to fear the approach of 

 an earthquake. 



It is not quite certain whether or not there is any connection 

 between the state of the atmosphere and the phenomena of earth- 

 quakes. It is not improbable that such is the case with the slighter 

 shocks, the trtmblores. They commonly occur, or at least are by far 

 most frequent, at the time of the changes of the seasons, in Guatemala 



as well as in Chile. But the more violent concussions seem to be 

 quite independent of the seasons, and they occur both in mini and 

 cloudless weather and in storms and during rain. In some instances 

 they have been preceded by luminous meteors. 



Ancient authors, especially Thucydides, frequently mention earth- 

 quakes ; but only in general terms. Yet we learn enough from these 

 slight notices to show that they were often equal in violence to 

 those which in modern times have convulsed the continent of Europe 

 and Asia. (Thucyd. i. 101 ; iii. 89 ; v. 50 ; viii. 41.) No detailed descrip- 

 tion of an earthquake in Europe or in the old continent exists before 

 that which, on the 1st of November, 1755, almost destroyed the city 

 of Lisbon. This is probably the most destructive earthquake which 

 has ever occurred in Europe. The number of persons that perished by 

 it is stated to have been 30,000. In February and March, 1783, the 

 north-eastern part of Sicily and the southern portion of Calabria were 

 convulsed by repeated and violent shocks, which overthrew the town 

 of Messina, and killed many thousands of its inhabitants, as well as 

 many persons in Calabria. One of the last considerable earthquakes 

 in Europe extended over the middle of the kingdom of Naples, and 

 was most destructive in the districts lying along the declivities of 

 Mount Matese (41 30' N. lat.). The number of persons who perished 

 by it amounted to 3274, besides 1615 who were wounded. In 1857, ou 

 December 16, two shocks of earthquake were felt in Southern Italy, 

 especially in the province of Basilicata, by the destruction of buildings 

 occasioned by which, at least 22,000 human beings were destroyed and 

 4000 wounded. It has been computed by Dr. Lacaita, that in the 

 course of seventy-five years, from 1783 to 1857, the kingdom of Naples 

 lost at least 111,000 inhabitants by the effects of earthquakes, or more 

 than 1500 per year, out of an average population of 6,000,000. 

 **On the first day of the year 1837, the countries along the eastern 

 extremity of the Mediterranean, especially Syria, were violently 

 agitated by an earthquake. The towns of Damascus, Acre, Tyre, and 

 Sidon, suffered great damage, and Tiberias and Safet were entirely 

 destroyed. It is stated that about 6000 lives were lost. 



America is more subject to earthquakes than any portion of the 

 Old World (except perhaps the Indian Archipelago and its vicinity), 

 but they are only strongly felt between 20 N. lat. and 40 S. lat. ; and 

 it is not the whole country included between these latitudes that 

 is visited by them, but only the table-lands of the Mexican isthmus, 

 the Andes, and the countries bordering on them, and those which 

 are adjacent to the Caribbean Sea. Mention of earthquakes in these 

 countries occurs in the Spanish historians of the Conquest ; but it 

 would seem as if the earthquakes were less destructive formerly than 

 in the last century. In 1717 the town of Guatemala was greatly 

 damaged by an earthquake on the 29th of September ; and on the 

 29th of June, 1773, the town was almost entirely destroyed. Caracas 

 was destroyed by an earthquake on the 26th of March, 1812, when 

 upwards of 12,000 of its inhabitants were buried in the ruins ; and 

 the same town experienced, in 1826, another earthquake, which 

 was hardly less destructive. Bogota experienced a very severe 

 shock in 1827. On the table-land of Quito violent earthquakes are 

 frequent. In 1698, on the 20th of June, Lacatunga and Hambato 

 were destroyed ; and on the 4th of February, 1797, the town of Quito 

 was greatly damaged, and Riobamba levelled to the ground. Not less 

 than 40,000 persons are stated to have perished by this last earth- 

 quake on the table-land. Luna and the countries about it are like- 

 wise subject to frequent and violent earthquakes. The town of Lima 

 was almost entirely destroyed on the 20th of October, 1687, and again 

 on the 28th of October, 1746. In this latter catastrophe the port of 

 Callao was inundated by the sea, and the whole population perished. 

 Arequipa has had its share of earthquakes ; but the last violent one 

 occurred hi 1725. Copiap6 was destroyed on the llth of April, 1819, 

 and again in 1822. By this last earthquake, which happened on the 

 19th of November, the town of Valparaiso was levelled to the ground. 

 Santiago has suffered largely from the destructive effects of the earth- 

 quakes so frequent in Chile : on the 8th of July, 1730, it sustained 

 great damages. But no place in Chile has so frequently been destroyed 

 as Concepcion. It was first destroyed by the united effects of repeated 

 shocks and the inundation of the sea in 1730, and again in the same 

 manner in 1751. After this the town was rebuilt on another site ; but 

 this new town and its port of Talcahuauo were entirely demolished on 

 the 20th of February, 1835. A most graphic description of this 

 dreadful earthquake is given in the ' Journal of the Royal Geographica 1 

 Society of London," vol. vi. p. 319, &c., to which we are much indebted 

 for several valuable facts and remarks. The inundation of the sea 

 during this calamity may be compared with the narrative of a similar 

 event recorded by Thucydides (iii. 89). 



Since the preceding sketch of the circumstances attending earth- 

 quakes was first published, great attention has been given to the 

 philosophical investigation of their phenomena; in which Mr. R. 

 Mallet, M. Inst. C.E., F.R.S., and M. Perrey, of Dijon, have taken the 

 lead. From the researches of the first, there is every reason to con- 

 sider it established that an earthquake is simply " the transit of a wave 

 or waves of elastic compression in any direction, from vertically upwards 

 to horizontally in, any azimuth, thruuijh the crust and surface of the earth, 

 from any centre of impulse or from more than one, and which may be 

 attended with sound and tidal waves, dependent upon the impulse and 

 upon circumstances of position as to tea and land," Four elaborate 



