ANNALS OF GEOPHYSICS, 55, 4, 2012; doi: 10.4401/ag-6110 2012 EMILIA EARTHQUAKES Looking for missing earthquake traces in the Ferrara-Modena plain: an update on historical seismicity Viviana Castelli*, Filippo Bernardini, Romano Camassi, Carlos H. Caracciolo, Emanuela Ercolani, Luca Postpischl Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Bologna, Bologna, Italy Article history Received July 17, 2012; accepted August 23, 2012. Subject classification: Historical seismology, Surveys, measurements, and monitoring, Seismic risk, Seismological data, General or miscellaneous. 1. Historical seismicity et al. 2007], and two similarly-sized earthquakes that oc- according to the catalog in current use curred in 1796 (MW 5.6) and 1909 (MW 5.5), the latter of According to the latest issue of the Italian seismic cata- which might have had a deep hypocentral location, judging logue [Rovida et al. 2011], the area most affected by the May- from its wide far field [Meloni and Molin 1987]. To the June 2012 Emilia sequence [for an overview, vide Galli et al. southwest, in the Carpi-Reggio area, there have been sev- 2012; Tertulliani et al. 2012, this volume] has a centuries-old eral moderately sized earthquakes, the latest of which was seismic history of comparatively low magnitude events. located near Correggio in 1996 (MW 5.4). These have been on a par with those that have occurred in the nearby Reggiano-Parmense area (where M 4.5 to M 5.5 2. Assessing the quality of the information behind the earthquakes were comparatively frequent in the last cen- current picture tury), although less significant than those on record in the The studies from which the earthquake parameters of portion of the northern Apennines that forms the southern Table 1 were taken by Locati et al. [2011] are of various boundary of the Pia-nura Padana (Figure 1), and a lot lower provenance and of variable thoroughness, and in a few cases than in the most seismically active zones of the Italian they are relatively out of date. Most derive from Guidoboni peninsula. Magnitude ca. 5.5 earthquakes are known to have et al. [2007], a collection that includes both advanced and pre- occurred near Ferrara (in 1346, 1561) and in the areas of Fi- liminary studies. The studies derived from Archivio Macro- nale Emilia-Bondeno (1574, 1908, 1986), Mantua (1901) and sismico GNDT [1995] and ING [1998] were extremely Cento (1922). However, this picture might be incomplete, preliminary ones; the ENEL [1985] studies were at least 27 as suggested by the recent discovery of a previously un- years old and might be improved by taking into account the known earthquake that occurred in 1639, whose maximum latest findings of local historical research (as in the case de- intensity was assessed as 7-8 Mercalli–Cancani–Sieberg scribed by Camassi et al. [2011b]). In a few cases (the earth- (MCS) in Finale Emilia by Camassi et al. [2011a]. quakes of 1425, 1508, 1901), the current catalog inherited the To date, the most relevant historically known local parameters assessed for them by an earlier catalog [Postpis- event is the so-called Ferrara earthquake of 1570 (MW 5.4), chl 1985]; two of these earthquakes have been recently stud- which was actually a complex seismic sequence that started ied by Molin et al. [2008]. on November 17, 1570 (when four strong shocks caused se- Looking at the general picture of local seismicity from a vere structural damage and partial collapses in Ferrara and historian's point of view, some peculiarities become obvious. its surroundings), went on with closely spaced aftershocks Up to the mid-1800s, for instance, there was a marked ten- up to early 1572, and then gradually petered out over the dency for the earthquakes to cluster around Ferrara and Mo- following couple of years, until March 17, 1574, when a dena, the main towns in the area. A comparison between the somewhat stronger shock caused further damage in Finale seismic histories of Ferrara and Modena and those of lesser Emilia [Guidoboni et al. 2007]. Another few M ca. 5.5 earth- towns located midway between them, such as Carpi, Miran- quakes have been located on the outskirts of the area af- dola and Finale Emilia (Figure 2), shows the former to be both fected by the 2012 sequence area. To the southeast, there longer and more detailed than the latter. This suggests that was the 1624 Argenta earthquake (MW 5.4) that had a max- the original evidence from which these seismic histories were imum intensity of 8-9 MCS in the Argenta locality [Guidoboni built might have been affected by what the founding fathers 519 CASTELLI ET AL. Figure 1. Seismicity of the studied area, according to Rovida et al. [2011]. of modern historical seismology called 'the urban fixation' 3. A few missing local earthquakes rediscovered [Vogt 1986, Vogt and Ambraseys 1991, Vogt 1994]; i.e., an in- The incompleteness of the current picture of local seis- clination to focus on what happened in towns, rather than in micity is shown by the number of previously unknown, villages and rural areas. This was particularly the case in the moderately damaging, local earthquakes, for which the in- centuries in which literacy tended to be more widespread formation was retrieved by recent studies (Table 2). Three of among townspeople than in the countryside. the more interesting cases are described below. It is also noticeable that earthquakes appear to have been comparatively scarcer in the 1600s to 1700s time win- 1) April 6, 1639 (Finale Emilia, Carpi?) dow than in earlier centuries. This might reflect a real trend A recent history of the Jewish community of Finale in the seismicity, although it might also be, partly at least, Emilia [Balboni 2005] quotes an authoritative local history the result of choices made in the selection of historical [Frassoni 1778] as having reported an earthquake that oc- earthquake data collected by the pre-instrumental tradition curred on April 6, 1639. This earthquake caused houses and of Italian descriptive earthquake studies. This culminated in chimneys to collapse in Finale, where a woman was killed. the great compilation by Baratta [1901], which is responsi- Reliable contemporary confirmation of this scenario can be ble, to this day, for the identification of most earthquakes found in the records of an inspection that was made by the that are included in the current catalog [vide Camassi et al. bishop of Modena to the Finale churches in October 1639, 2011a]. For a couple of examples, the great 18th century which describes the tumbledown conditions of the Chapel standard collection of medieval chronicles known as Rerum of the Most Holy Annunciation "owing to the earthquake" Italicarum Scriptores was undoubtedly instrumental in pro- [AAMoN 1639]. A document in the Carpi municipal archives viding information on many earthquakes observed in Mo- dated as July 3, 1638, and transcribed by D'Orazi [2012] dena and Ferrara before the 1500s. Conversely, the paucity records the damage to the municipal tower of Carpi caused of data available in the 1600s to 1700s time window might by "the past earthquake". Further research will be devoted to be at least partly due to the chance selection of the Bologna check the date of the Carpi document, and to look out for gazette as a privileged source of earthquake information by connections before it and the 1639 Finale Emilia earthquake. Baratta [1901]. This gazette was one of the oldest Italian pe- riodicals (1678-1796), and it usually published news from 2) December 15, 1761 (Mirandola, Carpi, Modena) Rome and from a few Italian (Venice, Milan, Genoa) and Eu- A collection of lives of eminent Mirandola citizens ropean towns, but not from those at the eastern end of the [Ceretti 1905] affirms that in 1762 one of them wrote a dis- Pianura Padana, such as Ferrara and Mantua [Camassi and sertation on earthquakes, taking his cue from "the one that Caracciolo 1994]. occurred in Mirandola on December 15, 1761". In the after- 520 Table 1. Local seismicity, according to Locati et al. [2011]. Np, number of macroseismic intensity data points; Imx, maximum intensity; Io, Epicentral intensity; Latit, latitude; Long, longitude; Mw, moment magnitude; Dmw, magnitude standard deviation. Year Mo Da Ho Mi Se Epicentral area Macroseismic study Np Imx Io Latit Long Mw DMw 1234 03 20 Ferrara ENEL 1985 5 7 7 44.836 11.618 5.1 0.34 1249 09 Modena Guidoboni et al. 2007 4 7-8 6-7 44.647 10.925 4.9 0.34 1285 12 13 Ferrara ENEL 1985 2 7 7 44.836 11.618 5.1 0.34 1339 11 16 14 10 Ferrara Guidoboni et al. 2007 1 6 6 44.836 11.618 4.7 0.34 1346 02 22 11 Ferrara Guidoboni et al. 2007 5 7-8 6-7 44.836 11.618 4.9 0.34 1409 08 17 00 35 Ferrara Guidoboni et al. 2007 1 6 6 44.836 11.618 4.7 0.34 1410 05 09 22 30 Ferrara ENEL 1985 3 6-7 6-7 44.836 11.618 4.9 0.34 1411 01 09 02 Ferrara Guidoboni et al. 2007 1 7 7 44.836 11.618 5.1 0.34 1425 08 10 19 Ferrara Sud Postpischl 1985, Molin et al. 2008 7 6 44.833 11.667 4.7 0.34 1474 03 11 20 30 Modena ENEL 1985 12 6 5 44.647 10.925 4.3 0.34 TRACES FORMISSINGEARTHQUAKE LOOKING 1483 03 03 22 Ferrara ENEL 1985 1 5-6 5-6 44.836 11.618 4.5 0.34 1508 10 18 15 Ferrara Sud Postpischl 1985, Molin et al.