Earthquake Distribution

Abstract

THE distribution of earthquakes may be studied either geographically or topographically—either along its broad lines in connection with the general physics of the globe, or in its smaller details with immediate and minute reference to local peculiarities. The field of inquiry is in both directions vast and comparatively unexplored. As regards what we may call circumstantial seismography, little has been done in the particular application of general principles to explain the apparent caprices of disturbances. These are innumerable and fantastic; yet, by patient observation, they can to a certain extent be brought within the range of strict physical reasoning. The laws of wave-motion, taken in connection with the facts of geological formation, will account for a good deal. Not, however, for all. Subterranean agencies introduce an element of uncertainty into the calculation which no diligence or ingenuity avails wholly to eliminate. Thus, in South America certain districts are observed to remain year after year, perhaps century after century, unscathed amid surrounding devastation. They are hence called “bridges,” the disturbance seeming, as it were, to flow beneath them, like a river under a bridge. Prof. Milne suggests tint their immunity may be due to the total reflection of earth-vibrations which would otherwise reach them (“Earthquakes,” p. 141). An obstacle to the propagation of such is besides often interposed by faults and fissures. The partial repose of Quito is attributed to the frequency of canons in its vicinity; as, similarly, the Capitol of Rome and the citadel of Capua were said to be protected by numerous deep wells or springs sunk round them.

Alphabetical Catalogue of the Earthquakes recorded as having occurred in Europe and adjacent Countries arranged to serve as a basis for an Earthquake Map of Europe.

By Joseph P. O'Reilly, Professor of Mining and Mineralogy, Royal College of Science, Dublin. Transactions of the Royal Irish Academy, Vol. XXVIII. “Science ” (Dublin, 1886.)