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Silvio Seno, University of Pavia (Italy)
Giovanni Toscani, University of Pavia (Italy)
Pierfrancesco Burrato, INGV (Italy)
Daniela Di Bucci, Dipartimento Protezione Civile (Italy)
Gianluca Valensise, INGV (Italy)
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The outermost thrust fronts of the Northern Apennines fold-and-thrust belt (Italy) are buried under a thick clastic cover that fills the Po Plain basin, and have been studied by means of seismic sections and deep well logs acquired for oil exploration purposes. These data show a system of NE-verging blind thrusts and folds that controlled the deposition of very thick syntectonic sedimentary wedges, with the Plio-Quaternary sequence locally up to 7-8 km thick. The fast sedimentation hid the growing structures, and as a consequence there are few direct surface evidences of the possible ongoing activity of the thrusts.
However, evidence for ongoing although weak tectonic activity is provided by seismicity and drainage anomalies, the latter represented by river diversion and channel pattern changes controlled by the growing buried anticlines. The historical and instrumental Italian seismic catalogues show that the southern Po Plain is affected by low to moderate seismicity, with Mmax up to 5.8, characterised by contractional focal mechanisms. The borehole breakouts and the focal mechanisms both show Shmax oriented perpendicular to the trend of the buried thrust fronts. GPS data suggest a weak SW-NE shortening at a rate of less than 1 mm/a.
In this framework, the goal of this paper is to study how the deformation is partitioned among the different Northern Apennines thrust fronts along the Bologna-Ferrara section, and which of the active thrusts can be the source of damaging earthquakes. To do this, we carried out an integrated analysis of geological, structural and morphotectonic data, and realised a N-S?striking section at regional scale using the interpretation of deep well logs and of seismic reflection lines.
In order to highlight the activity of the buried thrust ramp anticlines, we: 1- analysed the morphotectonic setting of the study area, comparing the location of drainage anomalies with that of the buried structures, and 2- plotted seismicity on the section to compare its distribution with the reconstructed structural setting and the tectonic deformation of the Quaternary deposits.
In order to investigate the evolution of the thrust fronts and its effects on the sedimentation, we also developed and analyzed a set of sandbox models, which reproduce the Plio-Quaternary deformation along the same transect. Finally, we propose a refined reconstruction of the Plio-Quaternary tectonic evolution of the Northern Apennines thrust fronts along the Bologna-Ferrara transect, obtained integrating the different results.
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