The 12 May 1802 earthquake (N Italy) in its historical and seismological context

Abstract

The Mw 5.7 earthquake that occurred on 12 May 1802 is the only one with Mw ≥ 5.5 located west of Lake Garda in the centralnorthern part of the Po Plain, Northern Italy, and the strongest event located in the seismic zone 907 of the ZS9 seismogenic zonation of Italy. Current parametric earthquake catalogs locate the event not far from important cities (e.g., Milan) and to sites where nuclear power plants were to be built in the 1980s or could be built in a near future. Although the earthquake parameters seemed sufficiently well constrained, a detailed investigation of documentary sources was performed, in repositories storing the documents of the Napoleonic departments to which the area affected by the earthquake belonged at that time. In the surviving archival series, we found the officers' correspondence on all the administrative aspects raised by the earthquake. The newly collected records allowed the authors to significantly increase the number of macroseismic intensity data, including new observations in the most damaged area. The results have been then interpreted in terms of both Mercalli-CancaniSieberg and EMS98 macroseismic scales. The P. Albini (B) · A. Rovida Sezione di Milano-Pavia, Istituto Nazionale di Geofisica e Vulcanologia, Via E. Bassini 15, 20133 Milan, Italy e-mail: albini@mi.ingv.it earthquake parameters were derived applying two different methods in order to get two independent estimates. Earthquake location is confirmed, although the still scarce data available in the area to the east of the epicenter do not permit to reduce the uncertainty to a minimum. According to the Boxer method, the magnitude is now slightly higher, and the source model shows a good agreement with the tectonic setting of the area.

An active deformation structure in the Po Plain (N Italy): The Romanengo anticline

“…Some of the blind thrusts affecting this region can be considered as active and the folds connected to them as fault propagation folds. In fact, as already underlined, the Romanengo structure is the probable source of an earthquake of magnitude ( M w ) 6.0 and intensity between 8 and 9 MCS recorded on 12 May 1802 [ Albini and Rovida , , and references therein]. For this reason a preliminary evaluation of the seismic hazard connected to this structure will be discussed in section .…”

“…Moreover, this region is affected by moderate to strong seismicity (Figure ), as documented by historical seismicity catalogues [ Boschi et al ., ; Guidoboni et al ., ; Rovida et al ., ], and in particular, the examined structure is the probable source of an earthquake of magnitude ( M w ) 6.0 and intensity between 8 and 9 Mercalli‐Cancani‐Sieberg scale (MCS) recorded on 12 May 1802 [ Albini and Rovida , , and references therein].…”

Epistemic Uncertainty in the Location and Magnitude of Earthquakes in Italy from Macroseismic Data

“…Note that the median M I for the Boxer and B&W bootstrap resampling solutions is 5.5. Albini and Rovida (2010) obtained M I 6.0 and 5.7 using the Boxer and B&W analyses techniques, respectively, but with different intensity attenuation relations.…”

“…S6, available as an electronic supplement to this paper) occurred about 50 km east of Milan and caused significant damage in the northern Italian provinces of Brescia, Bergamo, Lodi, and Cremona (Albini and Rovida, 2010). The 1802 event is the only M 5.5 or larger earthquake in the central-northern part of the Po Plain west of Lake Garda and is critical in estimations of the seismic hazard of the region.…”

“…The 1802 event is the only M 5.5 or larger earthquake in the central-northern part of the Po Plain west of Lake Garda and is critical in estimations of the seismic hazard of the region. As a result, the building codes for nearby towns specify more resistance to seismic forces than would otherwise be the case (Albini and Rovida, 2010). The macroseismic magnitude assigned in the Progetto Finalizzato Geodinamica is 5.8 (Postpischl, 1985).…”