Active fault-related folding in the epicentral area of the December 25, 1222 (Io=IX MCS) Brescia earthquake (Northern Italy): Seismotectonic implications

We reconstructed the geological evolution and the history of the fluvial network in the central part of the Po Plain in Lombardy, northern Italy, since the Middle Würm. We focused on evidences of dissection and incision of former rivers into the large outwash fans originating from piedmont glaciers of the southern Alps in the Last Glacial Maximum. The studied area is located between the Po River and the Alps north of the Adda/Serio river confluence, around the town of Crema. Morphometric analysis and stratigraphic investigation were carried out, supported by palaeobotany, sand petrography and radiometric dating. The obtained stratigraphic framework is presented by cross sections and by a geological map. During the Middle Würm, an alluvial fan of the Adda River oriented NWN-SSE occupied the area, feeding south and west the Romanengo hill. A substantial reorganisation of the fluvial network occurred during the Last Glacial Maximum. Since 32-30 ka cal. BP, the area was fed by two outwash rivers, originated from the Adda and the Oglio piedmont glaciers, both characterised by a prevalent southward drainage, 160°-170° S in the LGM. After the LGM the fan-head was dissected by trunk channels and, at the downslope fan limit, the southward flow shifted to a southeastern direction. Thereafter, major dissection and downcutting occurred in the Lateglacial, confining the major rivers into large alluvial corridors, further shaped by lateral erosion during the Holocene. The Late Holocene history of the Serio River is marked by fluvial floods during the late Roman Age, and by a capture of the lower reach by the Adda River. The geomorphological evidence supports the historically inferred age assignment of the diversion to 12th-14th c. AD. (Marchetti, 1990(Marchetti, , 2002. fig. 10 à fig. 12) fig. 11 et fig. 13A) D'un point de vue méthodologique, on a préparé un DTM détaillé en se servant des points cotés de la Cartographie Technique de la Région Lombardie (fig. 2). La succession stratigraphique a été décrite sur le terrain à partir de plusieurs affleurements et carottes, dont les plus intéressantes ont été soumises aux analyses radiocarbone, palynologiques et minéralogiques (sables). 14 dates AMS ont été obtenues sur plantes terrestres, calibrées avec CALIB à partir de la courbe de calibration IntCal09 (Reimer et al., 2009 ; tab. 2) et indiquées dans le texte « cal. BP ». Certains vestiges archéo-logiques présents dans les dépôts ont été examinés, étant donné qu'ils peuvent fournir des indices chronologiques utiles. L'analyse palynologique s'est faite sur 400 grains. Les plantes aquatiques et de marais ont été exclues de la somme pollinique. Le diagramme pollinique intègre la séquence de tourbes et de tourbes sableuses déposées dans le marais de Mosi di Crema (fig. 9), quelques données polliniques sur échantillons isolés, prélevés dans les dépôts lacustres de Cresmiero, et la séquence fluvio-palustre de Ripalta Guerina (tab. 5). Pour chacun des 13 échantillons de sables étu-diés, 400 points ont été comptés avec la méth...

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“…1). The latter are related to thrusts faults active in the subsurface of the plain during the Quaternary (Livio et al, 2009).…”

Section: Alluvial Fan Formation and Dissection At The Alpine Foothillmentioning

confidence: 99%

The last 40 ka evolution of the Central Po Plain between the Adda and Serio rivers

Ravazzi¹,

Deaddis²,

Amicis³

et al. 2012

geomorphologie

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“…This view mainly relies on the occurrence of postorogenic Pliocene marine deposits sealing the folded and eroded Mesozoic-Cenozoic Alpine bedrock (Castellarin et al, 1992). However, geomorphologic, seismological, and geodetic evidence (e.g., Desio, 1965;Anderson and Jackson, 1987;D'Agostino et al, 2008;Livio et al, 2009) clearly points to a still ongoing deformation in the Southern Alps and Po Plain, the study of which is the aim of the present work.…”

Section: Introductionmentioning

confidence: 80%

“…The Iseo Fault corresponds to a major extensional fault of Mesozoic or Permian age, already inferred in literature from land exposures (i.e., Lake Iseo-Oglio River line [Castellarin et al, 1992], Sebino faults [Bertotti et al, 1993], Val Camonica line [Cassinis and Perotti, 1996]). East of this fault, the Southern Alps south-verging thrusts in Cenozoic terrigenous units shift to one (Fantoni et al, 2004) or two major, north-verging back thrusts (Livio et al, 2009), refl ecting a different arrangement of the deeper structures and, ultimately, a paleogeographic conditioning (see also Ravaglia et al, 2006).…”

Section: Southern Alps Structuresmentioning

confidence: 99%

“…Increasing scientifi c sensibility of the seismic hazard of the Po Plain has led to modern studies based on punctual paleoseismological investigations (Galadini and Galli, 1999;Galadini et al, 2001;Livio et al, 2009). Moving from these studies, our present work aims to depict a new structural model for the Po Plain that accounts for the largely ignored PliocenePleistocene tectonics of the Southern Alps and seismogenic implications at regional scale.…”

Section: Introductionmentioning

confidence: 99%

“…We based our study on the integration of subsurface geophysical data with new direct stratigraphic and structural observations, gathered by means of detailed geological survey along the Southern Alps margin. Taking into account that sedimentation (in the Po Plain) or erosion (in the Alps) rates are much higher than the tectonic strain rate (e.g., Livio et al, 2009;Burrato et al, 2012), we focused on Pliocene and Early Pleistocene deposits, where the cumulative deformation is expected to be more evident in the stratigraphic record.…”

Section: Introductionmentioning

confidence: 99%

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Evidence for late Alpine tectonics in the Lake Garda area (northern Italy) and seismogenic implications

Scardia

Festa

Monegato

et al. 2014

Geological Society of America Bulletin

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We investigated the recent evolution of the Po Plain-Alps system by integrating subsurface geophysical data from the Po Plain with new stratigraphic and structural observations from the Southern Alps margin. Inversion of structural data and chronology provided by stratigraphic constraints led to the defi nition of three tectonic events since the Pliocene, namely, the intra-Zanclean, the Gelasian, and the Middle Pleistocene, driven by an axis of maximum compression formerly oriented NE (intra-Zanclean) and then to the NNW (Gelasian and Middle Pleistocene). The associated deformation has been accommodated by two sets of faults consisting of NNE-trending thrust faults, mostly represented in the western sector of Lake Garda, and NW-trending strike-slip faults, observed in the southern and eastern sectors. The interplay between these two sets of faults is interpreted to produce short (<10 km length) thrust ramps activated in left transpression, bounded by longer (30-60 km) transfer faults activated in a right-lateral strike-slip motion. Based on this structural model, we infer moderate seismicity (M w < 6) associated with the NNE-directed thrusts and stronger earthquakes (also M w > 6.5) along the NW-trending strike-slip faults. In this framework, the newly defi ned Nogara fault and the Sant'Ambrogio fault, all pertaining to the NW-trending system, are regarded as potential candidates for the seismogenic source of the January A.D. 1117 event, the most destructive earthquake in the Po Plain.

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

Bresciani

Perotti

2014

Tectonics

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Field surveys, well data and a detailed interpretation of a depth-converted seismic line, reveal that the Romanengo High, an isolated low relief that interrupts the morphological continuity of the Po Plain (N Italy) west of the Oglio River, coincides with a partially buried anticline, still active in recent times (Romanengo anticline). The Pliocene to Holocene evolution of the structure has been reconstructed by sequential restoration based on combined decompaction and unfolding methods, from the early Pliocene to Holocene. The analysis shows that from the beginning of the Pliocene onward, periods of tectonic activity have alternated with periods of quiescence. The more significant tectonic uplift rates are recorded during the late Pliocene (0.33 ± 0.06 mm/yr) and the beginning of Calabrian (0.284 ± 0.12 mm/yr), while at the end of Calabrian the structure was virtually inactive. During the early Pleistocene the reversal in the vergence of the structure indicates the onset of interaction with the Apennines deformational front in the area. From middle Pleistocene to Holocene, a marked increase in the tectonic uplift has been recorded, with an uplift rate of about 0.12 ± 0.05 mm/yr. A preliminary evaluation of the seismic hazards connected to blind thrusts affecting this active frontal sector of the Alpine chain, where it collides with the Apennines buried deformation fronts, is finally discussed.

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Active fault-related folding in the epicentral area of the December 25, 1222 (Io=IX MCS) Brescia earthquake (Northern Italy): Seismotectonic implications

Cited by 53 publications

References 43 publications

The last 40 ka evolution of the Central Po Plain between the Adda and Serio rivers

The last 40 ka evolution of the Central Po Plain between the Adda and Serio rivers

Evidence for late Alpine tectonics in the Lake Garda area (northern Italy) and seismogenic implications

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

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