Earthquake Of February Research Articles

The transmission of seismic waves

In studying the instrumental results of the Santiago, Cuba, earthquake of February 3, 1932, the author was particularly impressed by the almost linear character of portions of the travel‐time curve for the P‐wave, and for other wave‐groups in the interval between P and S. Two important conclusions have been suggested by this study, both of which pertain to fundamental conceptions of Earth‐structure and to the transmission of seismic waves.If we modify the usual smooth type of travel‐time curve by flattening out certain sections, we introduce sharp bending points in the curve and such points must be taken to indicate the presence of additional shells. The rather limited data for the Santiago shock indicate that one of these sharp changes in slope corresponds to a discontinuity about 350 km deep. A discontinuity near this level has already been suggested by Mohorovičić and others, but seismologists in general have apparently been reluctant to accept it. The data also indicate that another discontinuity may be present near the 800‐km level, but the data on which this is based are indefinite. The first generally accepted major discontinuity near the 1,200‐km level is evident in the Santiago curve by a bend near 5,500 km.

Santiago, Cuba, Earthquake of February 3, 1932

Santiago, Cuba, Earthquake of February 3, 1932

The Crystal Springs, California, earthquake of February 10, 19251

The Crystal Springs, California, earthquake of February 10, 19251

The St. Lawrence earthquake of February 28, 19251

The St. Lawrence earthquake of February 28, 19251

The Costa Rica earthquake of February 27, 1916

The Costa Rica earthquake of February 27, 1916

Earthquake of February 10, 1914

<scp>Earthquake of February</scp> 10, 1914

Earthquake of February 18, 1911

Earthquake of February 18, 1911

The Messina Earthquake and its Predecessors

ITALIAN Government Commissions have recently issued two valuable reports on the earthquakes of Calabria and Messina. One of them deals with the earthquake of November 16, 1894, a shock of great interest, but overshadowed by the disasters of 1905 and 1908. The greater part of this report, of 350 quarto pages, consists of a detailed account of the earthquake by Prof. A. Riccò. Sig. E. Camerana considers the nature and distribution of the damage to property, and suggests methods of construction that should be employed in future; Dr. M. Baratta investigates the relations of the earthquake with its predecessors; and Dr. G. di-Stefano describes the geological structure of. the district. The epicentral area includes the villages of San Procopio, Santa Eufemia, and Seminara, which lie near the west coast of Calabria and about twenty miles from Messina and Reggio. The number of persons killed at these and other places was 101, and the number of wounded about a thousand, the highest death-rate, of about 5 per cent., occurring at San Procopio. The epicentre coincides nearly with that of the well-known Calabrian earthquake of February 5, 1783. The isoseismal lines of the two earthquakes were similar in form, both being flattened and compressed towards the east, and expanding in the opposite direction. The earthquake of 1783 was, however, much the stronger, the loss of life far greater (the death-rate at one place rising to 75 per cent.), and the after-shocks were five times as numerous as in 1894, were of greater intensity, and were spread over a longer interval of time. The earthquake of 1894 was, in fact, a replica, on a much smaller scale, of the greatest of all Calabrian earthquakes.

Seismology in Japan

The Earthquake of February 22, 1880.—The earthquake which occurred shortly after midnight on the morning of February 22 was the most severe since the opening of this country to foreigners. I have been so much in the habit of noting my watch during the frequent earthquake manifestations by day and night, that I am sure I must have been instantly awakened. My house was swaying to and fro, windows were rattling, timbers creaking, mortar falling, and pictures swinging violently. Although, as usual on such occasions, I was studying my watch by a night light, I meditated escape. After forty seconds the motion apparently subsided. There had been two distinct periods of maximum intensity. Taking my lamp, I tried to reach the door, but the motion was still so great that I had to stop, supporting myself against the wall. When I went down stairs to look at two long pendulums of 20 and 30 feet length respectively, I found them swinging in arcs of about 2 feet, having broken all the apparatus on the table over which they hung. Hitherto the pointers placed on heavy weights suspended by long wires have been regarded by me as motionless points during an earthquake, and I have been able to use them accurately oa this assumption even for a shock which Palmieri's instrument indicates as 21°, a shock which knocked down several chimneys. It would seem that in the last earthquake the house, instead of, so to speak, “eating up” the vibrations, was forced into vibration itself. The period of this vibration was roughly noted by my neighbour, Mr. Thomas Gray, as nearly one second. At the lower end of one of these pendulums I have small pointers which scratch two smoked glass plates. These plates are caused to move away during an earthquake, so that relative vibrations are shown in two wavy lines. The direction of the first mark upon the plate tells the direction of the shock, and also the distance moved by the earth relatively to the steady pointer. The amplitude of the waves tells approximately what the movement has been during succeeding vibrations. From the number of waves upon a given length of glass we get the rate of vibration, and hence, knowing the velocity of transit, the true wave-length of the earthquake may be determined. As an example I may mention that an earthquake (December 3, 1879) registered by Palmieri's instrument as 18°, was recorded on 7 inches of one of my glass plates in a curve of seven very small waves, the amplitude of each of which was about 1 mm. Each wave was formed in half-a-second. The important deductions which may be drawn from even only one observation of this kind are obvious. The other pendulum I have used only for finding the greatest horizontal movement of an earth particle and its direction. Two pointers push against the motionless pendulum-bob when an earthquake occurs, and so they are moved in the stand which carries them, deflecting two suspended galvanometer mirrors, and readings of the amount of deviation of beams of reflected light are taken, I give some examples of the movement of the head of a pile which was driven deeply into the soft soil upon which Yedo is built:—