Earthquake disturbances recorded on the magnetographs at the observatories of the United States Coast and Geodetic Survey: No. 1

Abstract

One of the earliest records of a disturbance of the Earth's magnetic elements by an earthquake seems to be that of Father Eschinardi, at Rome, in 1681.2At the time of the Lisbon earthquake in 1855, Sarti is said to have observed a similar disturbance. On November 4, 1799, at Cuniana, in South America, Humboldt3 observed that while the declination and horizontal intensity were apparently unchanged by an earthquake, the dip was diminished 48′ from which value it slowly recovered. In October, 1802, Humboldt3 at Lima observed that a needle made 219 swings in ten minutes before an earthquake and only 213 swings in ten minutes after, indicating a decrease of about 5 per cent in horizontal intensity. The dip before the earthquake was 9°35′.4, after the earthquake g°07′.2. Similar results have not been obtained by magnetic surveys in Japan.