Note on the historical rotation seismographs

Abstract

Various authors, even in the pre-scientific age, hypothesised the existence of rotational waves, or at least the existence of "vortical motions". As the evidence of such motions, scientists have always distinguished the rotation of pinnacles and other ornamental elements of churches and monumental buildings. That kind of rotation is cited in various direct observation reports on the effects of Italian earthquakes. Numerous sources that document the effects of historical earthquakes describe this type of events within some complex descriptive frameworks, affected by the cultural and scientific context inside which the sources were produced. Even when the strangeness of these effects was observed and stressed, the sources do not always put forward any hypotheses as to the causes. Although specific research has not been performed on these aspects, a thorough systematic research into historical seismology for the creation of the Catalogue of Strong Earthquakes in Italy (Boschi et al. 2000) provides a large case history of occurrences of such effects. It was necessary to wait until the mid-19 century in Italy to have reports of rotational movements written with a "scientific" intention. Pedini (1742), on the occasion of the Livorno earthquake (Northern Italy) on 27 January 1742 recalls that it was as though the earth had "a vortical motion". But it was only after the Lisbon earthquakes (1 November 1755) and those of Calabria (5 February - 28 March 1783) that the scientists' attention started to be focused on the effects induced by the so-called "vortical" waves. Perhaps the most famous report as to the effects is the one relating to the rotation of two obelisks (Fig. 28.1) of the Charterhouse of Serra San Bruno in Calabria. This effect is documented in the account of Michele Sarconi (1784) about the mission of scientists guided around the places struck by the earthquakes in February-March 1783 and by one of the etchings on the effects on the villages and the natu-ral environment, contained in the "Atlante" (Schiantarelli and Stile 1784, etching XXI) enclosed in the report by Sarconi. In many other points of his report, Sarconi (1784) makes explicit reference to the vortex movement of the earth caused by the earthquake. The image in Fig. 28.1 was referred to by several authors and cited as an example of vortical movements induced by earthquakes; among the first and most illustrious were Charles Lyell (1797-1875) Charles Darwin (1809-1882), Robert Mallet (1810-1881), and Alexander Von Humboldt (1769-1859). Charles Lyell, who published a reproduction of the two rotated obelisks within a broad treatise on the Calabria earthquakes wrote in his work "Principles of Geology" (Lyell 1830): It appears that the wave-like motions, and those which are called vorticose or whirling in a vortex, often produced effects of the most capricious kind. Even Charles Darwin goes back upon the issue of the vortex motions in the description of the effects of the 20 February 1835, earthquake in Concepcion (Chile): Some square ornaments on the coping of these same walls, were moved by the earthquake into a diagonal position. A similar circumstance was observed after an earthquake at Valparaiso, Calabria, and other places, including some of the ancient Greek temples. This twisting displacement, at first appears to indicate a vorticose movement beneath each point thus affected; but this is highly improbable. (Darwin 1845) Robert Mallet, who was inspired by Lyell in many of his studies, contested Lyell's interpretation of the movements of the obelisks, being in agreement with the perplexities expressed by Darwin (Ferrari and McConnell 2005). Subsequently, Mallet honed an original method for the determination of the epicenter and the hypocenter of an earthquake starting from the study of the direction of the collapses, the shifting or the rotation of objects, buildings or parts of them (Mallet 1862, Ferrari and McConnell 2005) (Fig. 28.2). It is in the wake of the interest and the emotions aroused by the Calabria earthquakes of 1783 that some scholars dealt with the design and the testing of seismic instruments, not the very first ones, but among the first. At that time, however, it was still too early, to find instruments predisposed for the recording of "vortex" motions induced by earthquakes. The very first instruments of which we have reports that they have actually being made and used, are those of Jean de Hautefeuille in 1703, Nicola Cirillo in 1731 and Andrea Bina in 1751 (see Ferrari 1992). These instruments were very simple and exploited the principle of simple pendulum and the transfer of liquids from receptacles. It was necessary to wait until the mid-19 century, and in particular the mid-1870s, for the complex and pioneering phase of seismometry in which numerous scientists around the world became engaged in designing and testing of seismoscopes and seismographs, paying particular attention to the directions and components of the seismic motion. In 1875 one of these scholars, Filippo Cecchi, the director of the Ximeniano Observatory of Florence, designed the first instrument with an apparatus specially prepared to record the "vortical motions" as well (of the rotational waves): Cecchi's electrical seismograph with sliding smoked paper (Fig. 28.3). The instrument, described later on, still exists in two specimens: one is in Rome at the Ufficio Centrale di Ecologia Agraria and the other, is the prototype preserved at the Ximeniano Observatory in Florence. The first one was restored in 2002 by SGA and exposed at the ESC General Assembly in Genoa. © Springer-Verlag Berlin Heidelberg 2006.