Graziano Ferrari (1) and Camilla Roversi Monaco (2)
1) SGA Storia Geofisica Ambiente Via del Battiferro 10 /B 40129 Bologna - Italy -
2) Laboratorio degli Angeli Via degli Angeli 28 40124 Bologna - Italy -

Over the last twenty years, the historical documentation of seismology has acquired growing importance in the scientific interpretation of historical earthquakes. As seismology cannot reproduce the experiments observed in the laboratory, unlike other disciplines such as physics or chemistry, the historical seismograms and their related documentation play a fundamental role in the study of the strong earthquakes of the past 100 years at least.
Various factors have often determined the dispersion, the destruction or the poor conservation of historical seismograms (fig.1). An observatory, well-equipped with numerous instruments and having a long research tradition, often finds itself having to deal with thousands of seismograms reproduced on different media: smoked paper, photographic paper, etc. (fig.2). The people responsible for managing these seismogram archives are facing a growing demand for these recordings and at the same time are having to deal with the broader and more complex issue of how the seismograms ought to be properly preserved. The recent experiences performed experimentally within the framework of the Euroseismos project have allowed us to focus on some of these issues: we have sought to provide solutions and general methodological guidelines to resolve, in an economically feasible as well as acceptable way, the most urgent problems in the recovery and conservation of historical seismograms and their related historical documentation.

The cataloguing and the rearranging of a seismogram archive and its related paper documentation should be dealt with by following the conservational criteria normally adopted for the other archives having an artistic and historical interest comprising analogous materials (books, loose documents, drawings, prints...). Indeed, this approach allows us to have a comprehensive view of the material analysed also from the conservational perspective and to adopt the most suitabe solutions to guarantee a greater duration over time. In order to do this the specialists who find themselves dealing with rearranging and handling such materials should be supported, at least in the initial phases of the rearranging, by a restorer-conservationist specialising in paper-based materials. It is evident that a clearcut distinction exists between the materials of artistic interest and those of scientific interest, given the purposes for which they had been created. Therefore, any action concerning rearranging or restoration should take into account, first and foremost, the nature of the object being examined and how it will be used.
In the particular case of the historical seismic recordings, while their historical-artistic value may be rather limited (as the documentation largely concerns the last 100 years), its scientific value may be virtually irreplaceable. Just think, for example, to the seismograms of the strongest historical earthquakes that have return periods longer than 100-200 years (e.g. Earthquake of the Messina Strait in 1908). For the historical seismograms the safeguarding of the "aesthetic value" is certainly of lesser importance than the integrity of the seismic tracing actually recorded. Furthermore, the conservative and integrative actions must guarantee a limited degree of deformation as compared with the paper medium. The increasing use of historical seismograms for studies into seismogenesis and seismic hazard have led to the application of very high resolution digital scanning techniques and with negligible deformation parameters. This is the case of the SISMOS project of the Istituto Nazionale di Geofisica e Vulcanologia of Rome, set up for the integral high-resolution digital scanning of all the Italian historical seismograms.

In order to identifiy and resolve the problems of conservation the following factors need to be taken into account:

1 - The constituent materials and the manufacturing technique

2 - The causes of the decay

3 - Conservation solutions

What has been said so far is the result of a multidisciplinary approach carried out since 2001 by restorers and seismologists in the framework of the TROMOS and Euroseismos projects. We present our experience with over 15,000 seismograms, all of them of different kinds, originating from numerous observatories situated in the Euro-Mediteranean countries.

Actions implemented
The experience started in 2001 in regard to the historical and scientific archives of Giulio Grablovitz, made available to SGA by his heirs.
This amounted to the entire documentary archive (books, journals, letters, seismograms) of the geodynamic observatories of Casamicciola and Ischia, both on the Isle of Ischia itself. Thousands of pages on the activities performed by Grablovitz and his heirs from 1864 (even prior to the start-up of the observatories in 1887) to 1960ís were the subject of meticulous cleaning and disinfestations. Furthermore, the letters and the seismograms were catalogued and digitally scanned at SGA and the SISMOS Centre of the Istituto Nazionale di Geofisica e Vulcanologia in Rome, respectively.

Seismograms of the Ischia observatories
The seismograms were preserved among the paper documents that were in turn arranged inside plastic bags. Some of them, besides presenting rips and gaps, had undergone a major fungus attack that had compromised its mechanical stability so far as to make the paper medium so weak as not to even be able to be handled (see photograph). This situation had created the following problems:
- The plastic containers had not only fostered the progression of the fungicidal attack because they did not allow the air to circulate, but had made it easier for rips and gaps to develop as the extraction of the material from their interior had become very difficult.
- The paper documents had undergone a major oxidation (fig.5) owing to the direct contact with the seismograms that they contained.
The following solutions have been adopted:
- It was of the utmost importance to carry out a disinfestation of all of the material treated, even the material that, apparently, had not undergone a fungicidal attack. Indeed, the fungal spores "spread" very easily and, in unsuitable environmental conditions, can be activated from one moment to the next. If that action had not been performed, there would have been a risk of arranging the whole archive in suitable folders and to end up with an active fungicidal attack a few months after the conclusion of the re-ordering.
- Once the disinfestation had been performed, the most decayed seismograms were identified and restored so that they could be utilised (fig. 6).
- Finally, folders suitable for the preservation of the archive were created, paying attention to separate the paper documents from the seismograms (different materials must be adopted on the basis of the quantity, the format and the execution characteristics).

Seismograms of the Euroseismos project
During the unfolding of the Euroseismos project we have selected (from the partners of various Euro- Mediterranean institutes taking part in the project), recovered and catalogued (courtesy of SGA) as well as scanned at high resolution (by the SISMOS centre of the INGV) over 16,000 seismograms of the strongest historical earthquakes occurring in the 20th century in the Euro-Mediterranean area. Owing to the different decay factors listed above, numerous seismograms presented serious preservation problems and handling them could have made their already precarious conditions even worse (fig. 7). Several hundred seismograms have thus been the subject of conservative and integrative restoration work, so that they could be digitally scanned and better preserved for the future (fig. 8).

In conclusion, the importance of a set up of this kind, besides the need and the duty to prolong for as long as possibe the life of the documents and seismograms of interest for the future generations, lies in two factors:
- Some seismograms are so decayed as not to be at all legible, as they risk being irreparably damaged
- A reorganisation that does not take account of the conservation aspects risk being useless, with a consequent waste of time and money.
We have manipulated and analysed over 15,000 seismograms within the scope of the two projects TROMOS and Euroseismos for about 1,000 of these we have carried out conservative and integrative restoration actions that will ensure they will remain in good conditions for years to come. The hope is that in the future there will be an increasing awareness of the need to achieve a good state of preservation of historic seismograms, thus ensuring the survival of documents that are irreplaceable from the scientific and historical and cultural perspectives.