Advances in Conception about Earthquakes - Earthquake Engineering for Structural Design - page 105

gasses are produced by chemical reactions between the central fire, the Earth and
the moisture; these gasses, when submitted to high pressure, are forced to move the
Earth's surface, producing faults in the crust and generating earthquakes. Cardan
(1501-1576) supposed that earthquakes are due to the explosions produced by the
chemical reaction of sulphur and nitrogen. Such theories for earthquake generation
also explained volcanic events.
In 1620, Sir Francis Bacon studied the first crude map of the world in his
famous Novum Organum , observing the strange similarity between the coasts of
Africa and South America. He commented that this was no mere accidental
occurrence. In 1596, the Dutch map maker Abraham Ortelius suggested that the
Americas were torn away from Europe and Africa. In 1634 Descartes reached the
conclusion that the creation of the Earth had been the result of ongoing natural
processes, entering into conflict with the Church, which was, during those times,
the supreme authority. Thus, many scientists during that period were forced to
accept the Biblical history of Genesis, fearing expressing any alternative view.
The great opening to rational thought began in the 18 th Century. In 1780 Comte
de Buffon published his theory about the origin of the Earth, being the first
publication beyond the limitation of the Bible. Concerning earthquake occurrences,
the old theory of explosions of Cardan was accepted and dominated until it was
expanded by Lemery (1645-1715). The new theory considered that these
explosions were due to chemical reactions between iron and sulphur. In 1858, the
Italian geographer Antonio Pellegrini attempted to demonstrate the fit of the
American and African continents.
In China, a very strong seismic country, even the royalty was inspired to try to
understand the seismic phenomenon, with the Emperor Kangxi (1654-1722) who
attempted to describe the spatial distribution of earthquakes in China in an article
written in 1720 (Bolton and Cole, 2006).

4.1.3 EarlyModernPeriod

The greatest stimulus to seismological thinking came undoubtedly from the Lisbon
earthquake of 1755, providing evidence of motion at a large distance. The English
geologist and astronomer Michell (1724-1793) proposed for the first time that the
wave propagation from a specific location caused such distant motions. For this
reason, today Michell is regarded as the father of Seismology, which began to
mature in 19 th Century (Bertero and Bozorgnia, 2004).
During the 19

th

Century, the theory of the wave nature of earthquakes was for
the first time set up by Poisson (1781-1840), Mallet (1810-1881), Milne (1800-
1885) and Stokes (1819-1903), who theoretically predicted the possibility of the
generation of two kinds of body waves: longitudinal and shear waves; but the
cause producing these waves remained a mystery. In 1906, after the big San
Francisco earthquake, Reid, Professor at the Johns Hopkins University in
Baltimore, Maryland, studied the region in the vicinity of the San Andreas Fault in
California and discovered that the Western side of the fault shifted toward the
north-northeast before the earthquake took place. He also noted significant
horizontal shearing in the fault. As a consequence, he considered that the