QUATERNARY STUDIES AS A TOOL TO VALIDATE SEISMIC HAZARD POTENTIAL OF TECTONIC STRUCTURES: THE CASE OF THE MONFERRATO THRUST FRONT (VERCELLI PLAIN, NW ITALY)

Abstract

This paper proposes the study of the Quaternary geological evolution of the Vercelli Plain (Piedmont, NW Italy) with the aim of validating the reliability of assumptions about seismic hazard of tectonic structures based on seismotectonic data obtained from studies at regional scale. In particular, the Quaternary evolution is interpreted in order to verify and date the tectonic activity of the Monferrato thrust front, i.e., the westernmost arch of the buried northern Apennines front. In reference to the main purpose of the work, it is observed that only some stretches of the buried front (Lucedio and Cavourrina fault and, very likely, the flexures of Crescentino and Morano Po) were active between 870 and 400 ka BP. After 400 ka BP, near Crescentino and Trino, some structures transversal to the Monferrato front were probably activated, inducing the uplift of N-S elongated areas. The uplift affected both the northern Monferrato slope and the areas of the plain located south and north of the thrust front. The uplifted Trino area was limited to the east by the Salera Line. There are no indications of structures (fault or flexure) to the west of the Trino area or which form the limits of the uplifted Crescentino area, although their presence could be hypothesized. The Salera Line is the most important identified structure; it is very likely a complex-kinematics fault that was active from the Pliocene to the Upper Pleistocene and the Holocene. It continues to the south inside the hill areas, for a length of about 20 km. Therefore, the recent tectonic movements are not associated with the Monferrato thrust front, as claimed by other authors, but rather with N-S structures which are transversal to the front. Although elements to evaluate the seismic hazard possibly associated with these structures are not available, it is unlikely that the seismicity alone of the easternmost Apennine fronts (Emilia and Ferrara Folds) can provide useful information to assess the seismic hazard of the Vercelli Plain and of Northern Monferrato.