Publication Date:
2021-07-14
Description:
It is commonly believed that the Po Plain is an area of low seismic haz-
ard. This conclusion is essentially a combination of two factors: (1) the
historical record of earthquakes, which shows a relatively small number
of events of moderate magnitude, and only two significant earthquakes,
which occurred in the Middle Ages; and (2) the lack of
ad-hoc
research
on the geology of earthquakes in this area, as although many studies have
highlighted the local Quaternary tectonics, only a very few of them have
discussed the observed evidence in terms of seismic hazard. In contrast,
the data presented in the present study strongly suggest that the level of
earthquake hazard in the Po Plain is comparable to that of the well-
known seismic areas of the Apennine range, at least in terms of maxi-
mum magnitudes. Indeed, the high population density and the
concentration of industrial facilities make the Po Plain today one of the
more high-risk areas of the Italian territory. The Po Plain represents the
foredeep of two growing mountain belts, the southern Alps and the north-
ern Apennines. Recently, modern active tectonics studies have been con-
ducted along its margins to the south, along the northern Apennine
Piedmont belt, and to the northeast, along the eastern southern Alpine
Piedmont belt. However, in the central and western sectors of the Po
Plain, where the south-verging western southern Alpine front links up
with the north-verging Monferrato, Emilia and Ferrara arcs, the Qua-
ternary history of tectonic deformation and faulting are still relatively
poorly understood. These lie beneath the relatively flat alluvial surface of
the Po River, and provide the evidence for paleoseismicity and the result-
ing seismic hazard. In this review, we compile the data from the literature
to reassess the style and magnitude of the ongoing crustal deformation
and the associated earthquake faulting. This includes detailed informa-
tion on historical and instrumental seismicity, extensive subsurface in-
formation from the ENI industrial exploration, structural interpretation
of three regional seismic reflection profiles, analysis of novel global posi-
tioning system data, field mapping at selected key areas, and new paleo-
seismological investigations. We show that along the western southern
Alpine belt between Lake Garda and Lake Maggiore, the active tectonic
setting is characterized by a segmented belt of fault-propagation folds.
These are 50 km wide, and are controlled by the growth of out-of-se-
quence, 10-to-20-km-long, north and south verging thrusts. Regional
global positioning system data show ongoing shortening rates of the
order of 1 mm/yr. Quaternary fault slip rates typically range between
0.2 mm/yr and 0.4 mm/yr. Pleistocene shortening is obvious not only
along the western southern Alpine outer fronts that are buried beneath the
Po Plain, but also along the south Alpine foothills between Brescia and
Varese. Similar styles and rates of active folding and thrusting have also
been documented along the frontal sector of the northern Apennine arcs,
from Torino to Ferrara, and along the base of the Apennine mountain
front between Piacenza and Bologna. We selected the Brescia and Como
sectors in the western southern Alps and the Monferrato and Mirandola
structures in the northern Apennines as examples to illustrate the seismic
landscape of the study area, in terms of typical active structural, geo-
morphic and paleoseismic features. We argue that the level of earthquake
hazard in the Po Plain is comparable to that of the Apennine range. On
May 20, 2012, a few days after this review was formally accepted for pub-
lication, a M
W
5.9 earthquake ruptured the Mirandola structure. The
seismic sequence following this mainshock is ongoing, and we have added
further information about this event (updated on June 3rd, 2012), which
substantially confirms the conclusions arrived at here.
Description:
Published
Description:
969-1001
Description:
3.2. Tettonica attiva
Description:
JCR Journal
Description:
open
Keywords:
Active compressional tectonics
;
paleoseismology
;
seismic hazard
;
Po Plain foredeep
;
seismic landscape
;
04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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