A New Vertical Component Microseismograph

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    Abstract

    THE microseismograph, devised a few years ago by Prof. Vicentini, of Padua, is now well known as one of the most valuable of the vertical pendulums used in Italy for recording earthquake movements. With the aid of Dr. G. Pacher, several improvements have been made in it, the latest being the construction of a microseismograph for recording the vertical component of the motion (Atti del R. 1st. Veneto di scienze, &c, vol. lvii., 1899, pp. 65–89). In many of the details, it closely resembles the older instruments adapted for the horizontal components only. The chief points in which it differs from the latter are the following. The pendulum consists of a bar of iron 1˙50 m. long, 75 mm. wide, and diminishing in thickness from 10 mm. at one end to 7 mm. at the other. Near the thin end the bar carries three discs of lead, weighing altogether about 45 kg. The other end is fixed in a bracket built into the wall, and so inclined that the bar, under the action of the heavy mass, is horizontal at the free end. The magnifying and recording apparatus consists of two levers made of aluminium tube. One of these, bent at right angles (the longer arm being vertical), is connected with the pendulum, and transforms its vertical movements into horizontal ones. The second lever is horizontal, and its longer arm ends in a fine thread of glass, the point of which records the movements of the pendulum, magnified about 130 times, on a strip of smoked paper which passes below it at the rate of 24 mm. per minute. The first experiments showed that for rapid vibrations the heavy mass remained in a practically stationary condition. Every passing carriage produced a group of rapid vibrations, with periods varying from one to two-tenths of a second. During the short time in which the instrument has been at work, several earthquakes have been registered, and Drs. Vicentini and Pacher have increased the interest of the vertical component records by appending also those of two other microseismographs, giving the horizontal components only. These show that the vertical movement predominates during the whole of the time when the ground vibrates rapidly in a horizontal direction; and that the same sudden changes of intensity characterise the seis-mograms of both apparatus. The new instrument also records the slow pulsations which follow the rapid vibrations, but much less distinctly than the vertical pendulums, and it consequently sooner attains a state of rest.

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    A New Vertical Component Microseismograph. Nature 59, 523 (1899) doi:10.1038/059523a0

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