ASMI Archivio Storico Macrosismico ItalianoItalian Archive of Historical Earthquake Data

We present the results of an Italian­Maltese research, carried out to collect the macroseismic data needed to update the seismic catalogue of the Maltese Islands [Galea, 2007]. In this work we adopted the most up­to­date criteria developed by Italian historical seismology, obtaining results that significantly improve knowledge, particularly for the 1650­1923 time­window. Several previously unknown local earthquakes have been identified and evidence has been found of earthquake damage caused to the Maltese Islands both by earthquakes probably located in the Sicilian Channel (1658, 1780, 1861), and by some strong Greek earthquakes (1756, 1810, 1846). The European macroseismic scale 1998 (EMS­98, Grünthal [1998]) was used to assign macroseismic intensities. Basic information on seismic­induced natural phenomena (landslides, tsunamis) was also collected, to be used as a further constraint on the location and size of associated earthquakes, or for paleoseismological studies. As an added bonus, the study collected evidence of some Sicilian earthquakes unknown to seismological literature and data useful to improve the macroseismic database of already known Sicilian and Greek earthquakes.

The Catalogue lists earthquakes that occurred in Italy between 461 B.C. and 1997, and earthquakes that occurred in the general Mediterranean area between the VIII century b.C. and the XV century. This version (CFTI5Med) features: the retrieval and formatting of over 23,000 original bibliographic documents, transcribed or printed, nearly 50% of those utilized in the CFTI5Med. These documents are now available on-line as fully searchable pdf files; a full geological reinterpretation, georeferencing and reprocessing of over 2,300 descriptions of earthquake-induced environmental effects, which are now all available and searchable in a user-friendly web-GIS environment; the elaboration of a number of texts and commentaries that were missing from the CFTI4Med version of the catalogue; a totally re-designed and more efficient web- and web-GIS interface. The new Catalogo dei Forti Terremoti in ltalia includes 1,259 earthquakes that occurred in Italy (98 of which are currently considered false). No commentaries on the main earthquake effects were available in the previous version of the catalogue for 87 of such events as they had not been updated with respect to the information supplied in Guidoboni e Comastri (2005) for the 1000 AD-1500 AD time interval. The commentaries concerning the most significant effects of Italian medieval earthquakes have now been elaborated and are available along with the information on more recent events. For the remainder of the earthquakes first presented with the CFTI4Med - those that occurred in the general Mediterranean area away from the Italian coasts - the new catalogue provides only the felt reports and basic epicentral parameters.

The aim of this study was to provide a contribution to seismic hazard assessment of the Salento Peninsula (Apulia, southern Italy). It is well known that this area was struck by the February 20, 1743, earthquake (I 0 = IX and M w = 7.1), the strongest seismic event of Salento, that caused the most severe damage in the towns of Nardò (Lecce) and Francavilla Fontana (Brindisi), in the Ionian Islands (Greece) and in the western coast of Albania. It was also widely felt in the western coast of Greece, in Malta Islands, in southern Italy and in some localities of central and northern Italy. Moreover, the area of the Salento Peninsula has also been hit by several low-energy and a few high-energy earthquakes over the last centuries; the instrumental recent seismicity is mainly concentrated in the western sector of the peninsula and in the Otranto Channel. The Salento area has also experienced destructive seismicity of neighboring regions in Italy (the Gargano Promontory in northern Apulia, the Southern Apennines chain, the Calabrian Arc) and in the Balkan Peninsula (Greece and Albania). Accordingly, a critical analysis of several documentary and historical sources, as well as of the geologic–geomorphologic ground effects due to the strong 1743 Salento earthquake, has been carried out by the authors in this paper; the final purpose has been to re-evaluate the 1743 MCS macroseismic intensities and to provide a list of newly classified localities according to the ESI-07 scale on the base of recognized Earthquake Environmental Effects. The result is a quite different damage scenario due to this earthquake that could raise the seismic potential currently recognized for the Salento area, and consequently upgrade the seismic hazard classification of the Salento. Indeed it is important to remind that currently, despite the intense earthquake activity recorded not only in the Otranto Channel, but especially in Greece and Albania, this area is classified in the least dangerous category of the Seismic Classification of the Italian territory (IV category).

The Salento Peninsula (Apulia, southern Italy), along with a few other regions in Italy, is traditionally considered a low seismic hazard area. However, in 1743 it was affected by the catastrophic effects (Imax=IX-X MCS) of an earthquake, that probably occurred offshore, in the Salento Plateau (Ionian Sea). Subsequent damage had a complex pattern, whereby some towns were almost razed to the ground and others, nearby, suffered only slight damage. By means of an integrated geological, geotechnical and geophysical analysis we tried to cast a light on the causes of this peculiar distribution of seismic shaking, which we finally modelled by means of a one-dimensional simulation. These results, together with the re-analysis of the macroseismic distribution of the earthquake, and the seismotectonic knowledge of the region, suggest that the 1743 event was a strong, deep one that occurred far from Salento. The event induced high amplification, mainly in the villages (i.e., Nardò and Francavilla Fontana) founded on thin Pleistocene basins filled with soft sediments. The highest amplification peak, due to both the spectral content of the earthquake, as well as to the resonant period of the sedimentary basins, occurred in the same frequency range as most of the buildings of the time, that is ~3 Hz. This terrific double-resonance effect seems to be the main cause for the highest intensity evaluated in Salento, which, would otherwise, have been struck by effects possibly close to VII-VIII MCS.

A historical catalogue of felt earthquakes in the Maltese islands has been compiled dating back to 1530. Although no fatalities were officially recorded during this time as a direct consequence of earthquake effects, serious damage to buildings occurred several times. In the catalogue time period, the islands experienced EMS-98 intensity VII-VIII once (11 January 1693) and intensity VII, or VI-VII five times. The northern segment of the Hyblean-Malta plateau is the source region which appears to pose the greatest threat, although large Greek events and lower magnitude Sicily Channel events also produced damage. Estimates of return periods for intensity ≥V are presented, and it is shown that expected peak ground accelerations justify the implementation of, at least, minimum anti-seismic provisions. The rapid and continual increase in the local building stock on the densely-populated islands warrants the implementation of an appropriate seismic building code to be enforced.

Within the module NA4: "A Distributed Archive of Historical Earthquake Data" (coordinator of the module Dr. M. Stucchi) of the EU-NERIES project, the "Macroseismic Database of the Southern Balkan area" was compiled on a joint effort of ITSAK (Ch. A. Papaioannou and A.S. Savvaidis), as module Partner, and the Geophysical Laboratory of the University of Thessaloniki (B.C. Papazachos, as principal researcher, and C.B. Papazachos) for the time period 1000-1999. The database is temporarily hosted by the INGV-MI.

The source of the data (macroseismic Intensity Data Points) are:

• for the historical (before 1900) earthquakes, the books of Papazachos and Papazachou (1989, 1997, 2003) and
• for the earthquakes of the instrumental era, the bulletins of the National Observatory, the books of Papazachos and Papazachou (1989, 1997, 2003) and individual studies.

The addition of Ottoman sources to the corpus of material available for the study of the seismicity of the successor states of the Ottoman Empire, appears to offer a chance to enhance our understanding of the earthquake hazard of these regions. Among the voluminous archival legacy of the Ottoman bureaucracy, whose reach extended into every village, we might hope to find a somewhat full record of the effects of earthquakes throughout the empire.

The question which we want to pose here is how much Ottoman archival sources add to written material in other languages for the area and period under consideration, that is, Albania, Bulgaria, Greece and former Yugoslavia during the three centuries between 1500 and 1800.

The type of data which is of use to the earth scientist to assess earthquake hazard is that which can be accorded some numerical value that can be used to determine chiefly the epicentral area of an earthquake, in terms of its geographic coordinates, and the size of the event, in terms of its magnitude. This requires knowledge of the distribution of the intensity of an earthquake, that is the degree of the severity of damage or shaking, at as many sites as possible, including those at great distances where the shock was merely felt, as well as knowledge of the effects of the earthquake on the ground itself and of its association with secondary effects such as the generation of landslides and seismic sea waves.

The two pieces of information which are of interest to the earth scientist and which need to be assessed from written sources, are the location (epicentral region) and size (magnitude) of an earthquake; that is: (a) where and how large was the area of maximum destruction and (b) how far away the shock was felt. Other information such as the human and material losses incurred, and the social and economic impact and consequences of the event are of interest more to the historian than to the earth scientist, although sometimes this kind of information can help to assess the size of the epicentral region.

The method we employed to retrieve information has been first to identify earthquakes in the Ottoman Balkans during the period 1500 to 1800 from published occidental sources, and then to look for additional information in Greek and Slavonic (mostly) published documents. Having thus prepared a preliminary list of earthquakes, supplementary information was sought in Ottoman and Italian archival material and consular archives; this supplementary information proved invaluable for the second half of the 17th and for the 18th centuries. In the process, quite a few new events were found which added considerable information that led to additional searches in other sources.

The Ottoman archival material utilised for the present study consists for the most part of the documents from the Maliyeden Müdevver (MMD) series in the Ottoman central archives, the Başbakanlık Osmanlı Arşivi (BBA) in Istanbul. These documents and the registers into which they were copied for the central bureaucracy record, are extremely disparate in topic but have in common that they all concern financial matters, as do most of the other Ottoman documents utilised here. The aim of the writers of the documents which refer to earthquake damage was to assess the exact costs for the repair or reconstruction of structures affected by the shock, to dictate the administrative route to be followed in effecting the repairs and to ensure that the money assigned was spent as decreed. Another series of Ottoman documents which might have been useful and have given further information from disparate sites is the records of the kadi courts, but those for the Balkans are for the most part lost or cannot be located.

Among the most detailed documents are those relating to the repair of public buildings, in which are found a record of the dimensions of the damaged part of a structure and a complete accounting of the costs involved. The material relating to each event located is copious, but in isolation is for us of little value since it usually relates to damage to individual buildings and in particular to military structures. It is only rarely that there is any reference to damage elsewhere or to casualties and material losses.

Venetian correspondence relating to earthquakes in our region shares some of the same characteristics: both Ottoman and Venetian sources suffer from a lack of information regarding non-pecuniary matters, the very information which is of most interest to the scientist. Both Ottoman and Venetian documents rarely name affected sites other than those that had petitioned for or required financial as¬sistance for repairs or reconstruction, seldom mention casualty figures and almost never list sites at which an earthquake was felt without damage.

Each type of source reflects the concerns of its author. By contrast with the narrow administrative concerns of the Ottoman bureaucracy, the contemporary accounts of merchants and travellers, for instance, provide an impressionistic and personal picture of the effects of an earthquake, while church records are often ca-reful in giving the date of an event - which the Ottoman records are usually not; consular reports and newspapers give a wider view of the event but are few until a period well into the 17th century. Thus, for the region and period under investiga¬tion here, such vital features of an earthquake must be retrieved from these types of non-Ottoman sources.

When we consider the diversity of sources, the different languages involved and the paucity of libraries of the relevant types of material, it is clear that such re¬search is extremely time-consuming. This is especially true with respect to the retrieval of earthquake-related material from Ottoman sources. Indeed, when we consider the following statistic, we may wonder whether it is cost-effective: of some 500 earthquakes known from non-Ottoman sources for the period and area of our interest, only 41 were found in Ottoman sources and of these 21 are already known from other sources.

Most Ottoman documents relating to earthquakes provide no date for the events they describe and only a terminus ante quem can be established from the date of their issue. This makes it almost impossible to establish simultaneity and the association of such information with earthquakes known from other sources can only be tentative. Some of the entries in the catalogue which we present here may relate to the same event but at present there is not sufficient information to justify their amalgamation, or their association with known events.

Another difficulty in assessing the severity or intensity of an earthquake at a particular locality is that in many cases earthquake damage in Ottoman documents is reported together with or as a result of more than one cause, such as ageing, weathering, neglect or military operations, or as the result of more than one earth-quake. The collapse of or damage to a dilapidated building is not always an indication of severe shaking but rather a measure of the vulnerability of the structure. Large, distant earthquakes can destroy this class of buildings at distances of hundreds of kilometres from where the earthquake happened, particularly those built on soft and saturated ground, and their collapse can give the false impression of severe shaking. The lack of interest of the Ottoman administration in the maintenance of public buildings often contributes to false estimates of intensity.

Summary case-histories of the 41 earthquakes occurring in the Balkans between 1500 and 1800 which are recorded in hitherto unpublished Ottoman archival sources are presented below, and listed in Table 1. Fig. 1 and Table 2 show the location of sites mentioned in the text together with modem names.