Comparison between active stress field and tectonic structures in Northern Italy, Lombardy Region

The aim of this work is to understand the complex pattern of active stress field orientations revealed by borehole
breakout analysis with respect to the tectonic structures in a wide region of Northern Italy. The area is located in
the central-western part of the Po Plain between the south verging Southern Alps structures and the north verging
buried folds and thrusts of the Monferrato and Emilia arcs. Little information concerning the active stress field is
available because of the low seismicity level and the thick layer of sediments that covers the entire zone. A detailed
borehole breakout analysis has been performed in 36 wells with depths ranging from 2.2 to 7.3 km, whose
data have been supplied by Eni. Breakout analysis determined the minimum and maximum horizontal stress directions
(Shmin and SHmax). The results show a very complex pattern, pointing out that the stress field is not uniform.
In this area the regional stress field seems not «strong» enough, compared to the local one, so most of the
wells detect only the local field. This work contributes to clarify the various Shmin orientations observed in this
area, pointing out at wide scale, a general compression in NNE-SSW direction in this complex region.

ANDERSON, H.J. and J.A. JACKSON (1987): Active tectonics
of the Adriatic region, Geophys. J. R. Astrophys. Soc.,
91, 937-983.
BARTON, C.A. and M.D. ZOBACK (1994): Stress perturbations
associated with active faults penetrated by boreholes:
possible evidence for near-complete stress drop
and a new technique for stress magnitude measurement,
J. Geophys. Res., 99 (B5), 9373-9390.
BELL, J.S. and D.I. GOUGH (1979): Northeast-southwest
compressive stress in Alberta: evidence from oil wells,
Earth Planet. Sci. Lett., 45 (2), 475-482.
BELL, J.S., G. CAILLET and J. ADAMS (1992): Attempts to
detect open fractures and non-sealing faults with dipmeter
logs, in Geological Applications of Wireline
Logs, Geol. Soc. Spec. Pubbl., 65, 211-220.
BENEDETTI, L.C., P. TAPPONIER, Y. GAUDEMAR, I. MANIGHETTI
and J. vAN DER WOERD (2003): Geomorphic
evidence for an emergent active thrust along the edge
of the Po Plain: the Broni-Stradella Fault, J. Geophys.
Res., 108 (B5), 2238, doi: 10.1029/2001JB001546.
BURRATO, P., F. CIUCCI and G. VALENSISE (2003): An inventory
of river anomalies in the Po Plain, Northern Italy:
evidence for active blind thrust faulting, Ann. Geophysics,
46 (5), 865-882.
CAPORALI, A., S. MARTIN and M. MASSIRONI (2002): the
present day strain rate field in Italy and surrounding
countries as inferred from geodetic data, Boll. Geofis.
Teor. Appl., 43 (1-2), 3-21.
CASTELLARIN, A. and G.B. VAI (1986): South alpine versus
Po Plain Apenninic arcs, in The Origin of Arcs, edited
by F.C. WEZEL (Elsevier Science Publishers B.V., Amsterdam),
253-280.
CNR (1986): Neotectonic sketch map of Italy, scale
1:4500000, Mem. Soc. Geol. Ital., 30.
CNR-PFG (1991): Structural model of Italy and gravity
map, Quad. Ric. Sci., 114 (3).
COSTA, M. (2003): The buried Apenninic arcs of the Po
Plain and Northern Adriatic Sea (Italy); a new model,
Boll. Soc. Geol. Ital., 122 (1), 3-23.
DEWEY, J.F., M.L. HELMAN, E. TURCO, D.H.W. HUTRON and S.D. KNOTT (1989): Kinematics of Western Mediterranean,
in Alpine Tectonics, edited by M.P. COWARD, D.
DETRICH and R.G. PARK, Geol. Soc. Spec. Publ. London,
45, 265-283.
DZIEWONSKI, A.M., G. EKSTRÖM, and N.N. MATERNOVSKAYA
(2000): Centroid-moment tensor solutions
for October-December 1999, Phys. Earth Planet. Int.,
121, 205-221.
EVA, E., S. SOLARINO, C. EVA and G. NERI (1997): Stress
tensor orientation derived from fault plane solutions in
the Southwestern Alps, J. Geophys. Res., 102 (B4),
8171-8186.
FREPOLI, A. and A. AMATO (1997): Contemporaneous extension
and compression in the Northern Apennines from
earthquake fault plane solutions, Geophys. J. Int., 129,
368-388.
MARIUCCI, M.T. and B. MÜLLER (2003): The tectonic
regime in Italy inferred from borehole breakout data,
Tectonophysics, 361, 21-35.
MARIUCCI, M.T., A. AMATO, R. GAMBINI, M. GIORGIONI and P.
MONTONE (2002): Along-depth stress rotations and active
faults: an example in a 5-km deep well of Southern Italy,
Tectonics, 21 (4), 1021, doi: 10.1029/2001TC001338.
MONTONE, P. and M.T. MARIUCCI (1999): Active stress
along the NE external margin of the Apennines: the
Ferrara Arc, Northern Italy, J. Geodyn., 28, 251-265.
MONTONE, P., A. AMATO and S. PONDRELLI (1999): Active
stress map of Italy, J. Geophys. Res., 104 (B11),
25595-25610.
MONTONE, P., M.T. MARIUCCI, S. PONDRELLI and A. AMATO
(2004): An improved stress map for Italy and surrounding
regions (Central Mediterranean), J. Geophys.
Res., 109 (B10410), doi: 10.1029/2003JB002703.
NOCQUET, J.M. and E. CALAIS (2003): Crustal velocity field
of Western Europe from permanent GPS array solutions,
1996-2001, Geophys. J. Int., 154, 72-88.
PEROTTI, C.R. (1991): Osservazioni sull’assetto strutturale
del versante Padano dell’Appennino Nord-Occidentale,
Atti Ticinensi di Scienze della Terra, 34, 11-22.
PIANA, F. (2000): Structural setting of Western Monferrato
(Alps-Apennines junction zone, NW Italy), Tectonics,
19 (5), 943-960.
PIERI, M. and G. GROPPI (1981): Subsurface geological
structure of the Po Plain (Italy), CNR-PF Geodin. Pubbl.,
414, pp. 23.
PLUMB, R.A. and S.H. HICKMANN (1985): Stress-induced
borehole elongation: a comparison between dipmeter
and the borehole televiewer in the Auburn geothermal
well, J. Geophys. Res., 90, 5513-5521.
PONDRELLI, S., A. MORELLI, G. EKSTRÖM, S. MAZZA, E.
BOSCHI, and A.M. DZIEWONSKI (2002): European-
Mediterranean regional centroid-moment tensors:
1997-2000, Phys. Earth Planet. Int., 130, 71-101.
RAMSAY, J.G. (1967): Folding and Fracturing (McGraw-
Hill, New York), pp. 568.
SELVAGGI, G., F. FERULANO, M. DI BONA, A. FREPOLI, R.
AZZARA, A. BASILI, C. CHIARABBA, M.G. CIACCIO, F.
DI LUCCIO, F.P. LUCENTE, L. MARGHERITI and C. NOSTRO
(2001): The Mw 5.4 Reggio Emilia 1996 earthquake:
active compressional tectonics in the Po Plain,
Italy, Geophys. J. Int., 144, 1-13.
SERPELLONI, E., M. ANZIDEI, P. BALDI, G. CASULA and A.
GALVANI (2005): Crustal velocity and strain-rate fields in Italy and surrounding regions: new results from the
analysis of permanent and non-permanent GPS networks,
Geophys. J. Int., 161, 861-880, doi: 10.1111/
j.1365-246X.2005.02618.x.
SUE, C., F. THOUVENOT, J. FRECHET and P. TRICART (1999):
Widespread extension in the core of the Western Alps
revealed by earthquake analysis. J. Geophys. Res., 104
(B11), 25611-25622.
VITI, M., J. DE LUCA, D. BABBUCCI, E. MANTOVANI, D. ALBARELLO
and F. D’ONZA (2004): Driving mechanism of
tectonic activity in the Northern Apennines: quantitaTC4003, doi: 10.1029/2004TC001623.
WORKING GROUP CPTI (2004): Catalogo Parametrico dei
Terremoti Italiani, Versione 2004 (CPTI04), (INGV,
Bologna), (on line: http://emidius.mi.ingv.it/CPTI/).
ZOBACK, M.L. (1992): First and second order patterns of
stress in the lithosphere: the World Stress Map Project,
J. Geophys. Res., 97, 11703-11728.