The Elements of economic geology

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Monograph

Identifikator:: 1773832379

URN:: urn:nbn:de:zbw-retromon-172798

Document type:: Monograph

Author:: Gregory, John W. http://d-nb.info/gnd/11683014X

Title:: The Elements of economic geology

Place of publication:: London

Publisher:: Methuen

Year of publication:: 1928

Scope:: XIV, 312 S.; graph. Darst.

Digitisation:: 2021

Collection:: Economics Books

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Chapter

Document type:: Monograph

Structure type:: Chapter

Title:: Part IV. Engineering geology

Collection:: Economics Books

7.2 ECONOMIC GEOLOGY EcoNoMIc SEISMOLOGY Earthquakes are of interest to academic geology from the light they throw on the internal structure of the earth. They concern economic geology as regards building design, the recognition of situations liable to them, and their possible prediction. A. EarTHQUAKE ProBaBILITY AND PrEDIcCTION—The imminence of earthquakes may ultimately be foreseen from their distribution in time and space, or observation of their causes. A great shock results from the release of the crust from gradually increasing stress, which might be recognized by slight movements before the catastrophe. The slow tilting of a waterpipe across a line of suspected movement might give warning of an approaching shock. Earthquakes are most numerous in winter when atmos- pheric disturbances are usually most violent, and the breaking of a strained belt in the crust may be precipitated by a sudden change in air pressure. Thus the earthquake which devastated Yokohama and Tokyo in 1923, occurred during the passage of a violent cyclone which cannot have caused, but may have hastened the disaster. A long period without serious earthquake shock need not imply permanent immunity. The eastern coast of North America experiences severe shocks at distant intervals, such as those at Charleston in 1886, and on the Lower St. Law- rence in 1925; and any part of that line may be badly shaken after centuries of rest. A map of the world showing the distribution of earth- quakes shows that they are most frequent in areas of recent earth-movement, and along persistent faults. Earthquake warnings may be of great service since secondary consequences that might be avoided if foreseen are often the most disastrous. The Lisbon Earthquake of 1st November, 1755, was not of the greatest severity, for parts of the city built on limestone and basalt were not damaged (Sharpe, Proc. G. Soc., 1838, No. 60, p. 36). The heavy death-roll was due to a wave 50 feet high, which swept up the Tagus and drowned the 60,000 people who had taken shelter on the mole. According to tradition the mole was swallowed by an unfathomable abyss: but probably its

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