A revision of the 1783?1784 Calabrian (southern Italy) tsunamis

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A revision of the 1783?1784 Calabrian (southern Italy) tsunamis L. Graziani, A. Maramai, S. Tinti To cite this version: L. Graziani, A. Maramai, S. Tinti. A revision of the 1783?1784 Calabrian (southern
A revision of the 1783?1784 Calabrian (southern Italy) tsunamis L. Graziani, A. Maramai, S. Tinti To cite this version: L. Graziani, A. Maramai, S. Tinti. A revision of the 1783?1784 Calabrian (southern Italy) tsunamis. atural Hazards and Earth System Science, Copernicus Publications on behalf of the European Geosciences Union, 2006, 6 (6), pp hal HAL Id: hal https://hal.archives-ouvertes.fr/hal Submitted on 13 Dec 2006 HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. at. Hazards Earth Syst. Sci., 6, , 2006 Author(s) This work is licensed under a Creative Commons License. atural Hazards and Earth System Sciences A revision of the Calabrian (southern Italy) tsunamis L. Graziani 1, A. Maramai 1, and S. Tinti 2 1 Istituto azionale di Geofisica e Vulcanologia, Sezione Roma 2, Rome, Italy 2 University of Bologna, Dipartimento di Fisica, Settore Geofisica, Bologna, Italy Received: 28 September 2006 Revised: 23 ovember 2006 Accepted: 23 ovember 2006 Published: 13 December 2006 Abstract. Southern Italy is one of the most tsunamigenic areas in the Mediterranean basin, having experienced during centuries a large number of tsunamis, some of which very destructive. In particular, the most exposed zone here is the Messina Straits separating the coasts of Calabria and Sicily that was the theatre of the strongest Italian events. In Calabria was shaken by the most violent and persistent seismic crisis occurred in the last 2000 years. Five very strong earthquakes, followed by tsunamis, occurred in a short interval of time (February March 1783), causing destruction and a lot of victims in a vast region embracing the whole southern Calabria and the Messina area, Sicily. In this study we re-examined these events by taking into account all available historical sources. In particular, we focussed on the 5 and 6 February 1783 tsunamis, that were the most destructive. As regards the 5 February event, we found that it was underestimated and erroneously considered a minor event. On the contrary, the analysis of the sources revealed that in some localities the tsunami effects were quite strong. The 6 February tsunami, the strongest one of the sequence, was due to a huge earthquake-induced rockfall and killed more than 1500 people in the Calabrian village of Scilla. For this event the inundated area and the runup values distribution were estimated. Further, the analysis of the historical sources allowed us to find three new tsunamis that passed previously unnoticed and that occurred during this seismic period. The first one occurred a few hours before the large earthquake of 5 February The second was generated by a rockfall on 24 March Finally, the third occurred on 9 January 1784, probably due to a submarine earthquake. Correspondence to: A. Maramai 1 Introduction In the Mediterranean basin, Italy is one of the countries most affected by tsunamis. During centuries it has experienced a large number of events, some of which caused catastrophic effects, severe damage and thousands of victims. The analysis of the Italian Tsunami Catalogue (ITC, Tinti et al., 2004) shows that southern Calabria, Messina Straits and eastern Sicily are certainly the most active tsunamigenic regions in Italy. As a matter of fact, the majority of the Italian tsunamis, including the strongest ones, occurred here: most were the results of coastal and submarine earthquakes, but some were also due to volcanic activity and submarine slides. The geological setting of the area is quite complex and some aspects are still poorly understood. Structural analysis and seismological and deformation (VLBI and GPS) data show a regional extensional ESE-WW trend which is coupled with a strong mm/yr uplift of the whole Calabrian arc region (Monaco et al., 1996; Tortorici et al., 2003; D Agostino and Selvaggi, 2004; Jenny et al., 2006). One of the main tectonic features is the belt of normal faults running for more than 350 km along the Apennines chain and extending from Calabria to Sicily, which is formed by distinct fault segments with maximum length of about km that are responsible for the major earthquakes. Some of the faults are found close to the coast or are completely placed offshore with great potential for tsunami generation. The most energetic historical shocks reached the maximum magnitude of M 7 (Boschi et al., 2000) and almost all were accompanied by sizable tsunamis. Before focusing on the seismic period, it is worth mentioning the two largest tsunamigenic earthquakes that occurred in Calabria and Sicily, namely the 1693 eastern Sicily and the December 1908 Messina Straits events (Fig. 1). At the beginning of 1693 a tremendous seismic crisis hit eastern Sicily, culminating in the main shock of 11 January Published by Copernicus GmbH on behalf of the European Geosciences Union. 1054 L. Graziani et al.: Revision of the 1783 Calabrian tsunamis E TYRRHEIA SEA SICILY 1693 Messina S. Alessio Giardini axos Catania Augusta oto 1908 Scilla Reggio Calabria Pellaro Siracusa IOIA SEA Fig. 1. Epicentres of the earthquakes generating the most destructive tsunamis in southern Calabria and eastern Sicily. Localities most affected by waves are reported. with estimated magnitude M=7.4 (CPTI2, 2004). It produced almost complete destruction within an area of about km 2 extending from Catania to oto and Siracusa, causing more than casualties (Boschi et al., 2000). A tsunami was observed along the whole eastern Sicily coast with major effects at Augusta and Catania. First the sea withdrew from the shoreline and the following inundation was very damaging and lethal for many people. At Augusta, the water waves were likely as high as 15 m (Tinti et al., 2004). The 28 December 1908 Messina earthquake is one of the strongest earthquakes that ever occurred in Italy. The towns of Messina and Reggio Calabria together with many other villages were completely destroyed. Partial destruction involved most of Calabria and Sicily over an area about 6000 km 2 wide. More than people died. A violent tsunami followed the shock, causing severe damage and hundreds of victims in the Messina Straits zone. In most places the sea first receded for a few minutes from the usual level and then flooded the coast with at least three big waves. The sea level oscillations lasted for many hours. The tsunami reached its maximum intensity in the Calabrian coast near Pellaro, where run-up heights as large as 13 m were observed, and in Sicily at Giardini axos and at Sant Alessio, where the measured run up was 11.7 m (Tinti et al., 2004). The main purpose of this paper is to provide a picture of the tsunamis that occurred during the seismic crisis that devastated the Calabria region in Since this seismic sequence was exceptionally long and destructive, the associated tsunamis were almost disregarded as secondary minor events, except for the 6 February Scilla tsunami that caused much more casualties than the parent earthquake itself. This unusual and long seismic period stirred up great interest in many Italian and foreign scientists and scholars, that went on the field to make direct observations and to document the effects. As a result, a vast amount of reports, chronicles, works and maps representing the devastation was produced and this constitutes today a precious source of information for studying the earthquake effects and consequences, including tsunamis. By carrying out a deep analysis of the available sources it was possible to count as many as ten distinct tsunami events, most of low intensity, three of which were never mentioned before in the modern scientific literature. For the largest tsunamis, the available data allowed us to draw a rather reliable picture of the effects and, in particular, for the 6 February Scilla event it was possible to perform the reconstruction of the inundated area and to determine the distribution of the run-up values. This work contributes to the updating of the ITC (Tinti et al., 2004) and, for this purpose, the events studied here were classified according to the evaluation standards adopted for the catalogue compilation. 2 The Calabrian seismic sequence In the southern part of Calabria was struck by one of the most impressive and persistent seismic crisis that occurred in the last 2000 years. A lot of sources are available in the literature: many famous coeval writers and a lot of current historiographer studied and documented this seismic period. During our study we examined more than 100 bibliographical sources, the most reliable ones, and we also performed extensive research in many public and private archives, libraries, etc., in order to collect new data. The crisis lasted more than three years, starting at the beginning of February 1783 and, during a period of about two months five large earthquakes (with epicentral intensity MCS IX) occurred along a zone about 100 km long, devastating southern Calabria between Reggio Calabria and Catanzaro. The first destructive earthquake of the sequence ocurred on 5 February 1783, and was followed by the other main shocks respectively on 6 and 7 February, and on 1 and 28 March in the same year. All these earthquakes resulted to be tsunamigenic, though the size of the generated tsunamis differed very much from case to case. The epicentres of the five main shocks migrated northward from the Aspromonte area to the Sant Eufemia and the Squillace gulfs (Fig. 2). In addition to these main earthquakes, hundreds of smaller aftershocks hit southern Calabria. The seismic sequence was one of most catastrophic in western Europe. The cumulative effects of all these earthquakes was devastating and great changes were produced even in the environment morphology: diffuse at. Hazards Earth Syst. Sci., 6, , 2006 L. Graziani et al.: Revision of the 1783 Calabrian tsunamis E Table 1. Reliability scale of the Italian Tsunami Catalogue (Tinti et al., 2004). TYRRHEIA SEA SICILY S. EUFEMIA GULF Catanzaro 01/03/ /03/1783 Tropea Gioia Tauro Bagnara 05/02/ /02/1783 Messina Scilla ASPROMOTE Reggio Calabria 07/02/1783 Stilo SQUILLACE GULF IOIA SEA Fig. 2. Epicentres of the five main shocks of the 1783 Calabrian seismic crisis. Square size increases with magnitude. landsliding led to heavy changes to the hydrogeological system (more than 200 lakes formed as a consequence of stream damming caused by slides). The most extraordinary effects were chiefly due to the 5 February earthquake (Vivenzio, 1788; Hamilton, 1783; Dolomieu, 1784; Baratta, 1901; Jacques et al., 2001). On the 5 February, at about 12:00, a catastrophic tsunamigenic earthquake abruptly opened the seismic period. The shock (Mw=6.9, I=XI MCS; CPTI2, 2004) was felt in a very wide area, including the whole Sicily and a big portion of the southern Italian peninsula. More than 380 villages were damaged, 180 were almost totally ruined and the count of fatalities exceeded Major effects were observed close to the Gioia Tauro plain (on the Tyrrhenian side), at the western foot of the northern Aspromonte, where some towns were completely destroyed and many other suffered severe damage. The Ionian side was less affected. Reports tell that at the time of the shock people in the fields were thrown down and trees were uprooted. Though this event has been widely studied, the identification of the generating fault is still debated. Tsunami information can be used to better define the possible source (Tinti and Piatanesi, 1996a), as was also shown for other cases, where comparison between the available tsunami data and tsunami simulations was used to constrain the focal mechanism as well as to exclude some of the fault locations proposed in literature (see e.g. Piatanesi et al., 1996; Tinti and Piatanesi, 1996b). The shock of 6 February occurred during the night (00:20), was less strong than the previous day earthquake (equivalent magnitude from macroseismic data Me=6.3, I=VIII IX; CPTI2, 2004) and was located slightly to south-west, in the Messina Straits. It caused severe damage at Messina and at Scilla. The earthquake was responsible for a huge rockfall that occurred along the western cliff of the Mount Campallà at Scilla, that fell into the sea generating a disastrous tsunami. Reliability scale of the Italian Tsunami Catalogue 0: Very Improbable Tsunami 1: Improbable Tsunami 2: Questionable Tsunami 3: Probable Tsunami 4: Definite Tsunami On 7 February another big shock, with epicentre located about 40 km north-east to the 5 February event, hit southern Calabria. The shock (M w =6.6, I=X XI MCS; CPTI2, 2004) occurred at 13:10 and caused new heavy destruction. On 1 March at 01:40 the fourth big shock occurred. The estimated magnitude was M w =5.9 (CPTI2, 2004) with I=IX MCS and the epicentral area was located about 20 km north of the 7 February earthquake, along the Apennines chain. The last big earthquake of the sequence occurred on 28 March at 18:55. The epicentre was slightly west to the fourth, and the estimated magnitude was M w =6.9 with I=X MCS (CPTI2, 2004). 3 The tsunami events In order to perform the reconstruction of the tsunami events that occurred during the seismic crisis, we gathered the historical material from contemporary chronicles and reports available in national and local libraries, private and ecclesiastic archives, etc. The analysis led us to an improved knowledge of the main events already present in the ITC and to discover three new tsunami events. The tsunamis were examined following the ITC guideline: in particular each event is characterised by a tsunami intensity value, a reliability score and, when known, by the generating mechanism. As far as the intensity is concerned, the 6-degree intensity scale proposed by Sieberg and Ambraseys (Ambraseys, 1962) is used to quantify the effects of a tsunami on structures and environment. An intensity 1 tsunami is very light and only visible on tide gauge records, while at the top of the scale an intensity 6 tsunami is capable of causing large disasters with total destruction of man-made structures, extensive flooding, many casualties, etc. otice that we also attributed the tsunami intensity on the basis of the 12-degree scale that was proposed by Papadopoulos and Imamura in the course of the 2001 International Tsunami Conference, but that was not adopted in the ITC first version (Tinti and Maramai, 1996) nor in its recent update (Tinti et al., 2004). The tsunami reliability is graded according to the 5-degree modified Iida scale and ranges from degree 0, equivalent to a very improbable tsunami, to degree 4 corresponding to a definite tsunami (see Table 1). The reliability is a very at. Hazards Earth Syst. Sci., 6, , 2006 1056 L. Graziani et al.: Revision of the 1783 Calabrian tsunamis E S. EUFEMIA GULF Pizzo Calabro Bivona Cutro Capo Rizzuto SQUILLACE GULF E Capo Vaticano Joppolo icotera Gioia del Tirreno Gioia Tauro Torre del Faro Scilla Messina Cenidio Catona Reggio Calabria Bianco Roccella Ionica Fig. 3. Localities involved by the tsunami occurred in the morning of 5 February 1783, at 08:00. important parameter which helps to judge the quality of the data. The approach for determining reliability value consists of taking into account and rating separately different elements or categories of data, namely: 1) what is known about the tsunami cause, 2) what is known about the tsunami itself, and 3) what is known about the documentary sources. Each category is rated on three levels, and then the final reliability is obtained by combining these partial scores (see Tinti et al., 2004, for details on assigning the ITC parameters). In this research, the result of the scrutiny of new bibliographical sources led us to re-appraise the parameters of some tsunamis that were already included in the ITC. As an example, the 5 February event, that in the catalogue was classified with Ambraseys intensity 3, has been re-evaluated and now classified with intensity 4. During the seismic crisis a total of ten tsunamis occurred all within a time span of about one year from February 1783 to January 1784: seven were small events, two were strong, and one was disastrous, causing more than 1500 victims in the small Calabrian village of Scilla. In the following, a description of each event is provided, with the specification of the tsunami intensity, reliability and cause February 1783 time 08:00 This is one of the three new tsunamis discovered during this study. According to some sources, at about 08:00 in the morning (four hours before the first main shock) a weak earthquake was felt in Calabria (Fig. 3). On the Ionian side of Calabria, at Capo Rizzuto a sudden sea inundation was observed (De Lorenzo, 1877), while at Cutro, some hours before the big earthquake, the sea withdrew and then came back IOIA SEA Fig. 4. Epicentre of the 5 February 1783 main shock. Localities hit by the generated tsunami are reported. to its usual limit (Vivenzio, 1788). On the other hand, De Lorenzo (1877) reports that at Bivona and at Pizzo Calabro, in the Tyrrhenian Calabria, some fishermen on the boat noted that in the morning the sea became suddenly agitated. The only seismic catalogue reporting an earthquake in the morning is the Istituto azionale di Geofisica catalogue (IG, 1991), in which a weak shock.(i=iii MCS scale) with epicenter located at capo Rizzuto on the Ionian coast is mentioned as occurred at 08:00 in the morning. The intensity attributed to this tsunami is 3 (Sieberg-Ambraseys scale) and the reliability is 2. The estimated Papadopoulos-Imamura scale intensity, hereafter denoted by P-I intensity, is III February 1783 time 12:00 The 5 February tsunami event was at first underestimated and considered only a minor event, causing no serious damage. On the contrary, the analysis of the sources revealed that in some localities the tsunami effects were quite strong. The Sicily coast from Messina to Torre del Faro (about 11 miles) and in Calabria from Cenidio to Scilla (about 7 miles) was heavily affected by the tsunami (Fig. 4). Historical sources refer that generally the sea first receded and then inundated the shore. Withdrawals and inundations repeated at least three times at intervals of about min. At Joppolo a considerable sea withdrawal was observed, that left the sea bottom dry (Sarconi, 1784), and about 8 min after the shock in the sea between icotera and Gioia Tauro two fishermen observed two waves, one travelling toward Capo Vaticano and the other toward Gioia del Tirreno (Galimi, 1783; De Lorenzo, 1877). This latter was as high as a big vessel, but caused no damage (Minasi, 1785). At icotera the sea withdrew boiling and then turned the fishing boats upside-down (Vivenzio, 1788). At Gioia del at. Hazards Earth Syst. Sci., 6, , 2006 L. Graziani et al.: Revision of the 1783 Calabrian tsunamis Prince s House (R=6.2) 2 S. Spirito Church (I=40; R=8) 3 Gornelle s fountain (R=8.3) 4 S. icola Church (I=100; R 5) 5 Livorno stream (I=200) S. Maria delle Grazie Church (I=90) (R=5.2) Marina dell Oliveto(R=3.5) 4 6 Marina Grande Chianalea 8 Fig. 5. Map of Scilla village: the area flooded by the 6 February 1783 tsunami is depicted in grey. umbers indicate spots for which inundation and/or run-up values have been inferred by the bibliographical sources. Letter I indicates the inundation value (in meters), while R indicates the run-up value (in meters). Tirreno the sea inundated the shore without any damage (Minasi, 1785). At Scilla the sea withdrew for more than 10 meters leaving the sea bottom dry an
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