Download Hydrogeochemistry of Magra Valley (Italy

Hydrogeochemistry of Magra Valley (Italy) aquifers: geochemical background
of an area investigated for seismic precursors.
Lisa Pierottia*, Flavia Bottib, Sara Bracalonib, Ilaria Burresib, Marina Cattaneob, Fabrizio Gherardia
a) National Research Council of Italy, Institute of Geoscience and Earth Resources, Via Moruzzi, 1 - Pisa, Italy ; b) Departement of Earth Sciences, University of Pisa, Italy - *[email protected]
Spring Q < 1l/s
Spring Q > 1l/s
Spring Q > 10l/s
Well
Q < 1l/s
Well
Q > 1l/s
TYPE A WATERS: springs fed by superficial hydrogeological structures. Water circulation occurs along short and shallow circulation paths.
(A1) arenaceous rocks, (A2) marly-limestones rocks, (A3) shales and siltstones interbedded with limestones and calcarenites, (A4) ophiolitic rocks, (A5) wells draining loosely cemented detrital deposits
HCO3 vs Ca
700
7
600
6
500
5
HCO3 (meq/l)
TDS (mg/l)
TDS vs T
400
300
4
3
200
2
100
1
0
0
0
2
4
6
8
10
12 14
16 18
20
0
1
2
3
T°C
4
5
6
Ca (meq/l)
TYPE B WATERS: springs fed by superficial hydrogeological structures, consisting of evaporite-carbonate rocks. Water circulation occurs
along relatively short and shallow circulation paths.
TDS vs T
SO4 vs Ca
2500
35
FV 3
FV 3
30
2000
25
1500
LI 5
1000
SI3
LI 6
MI4
20
LI 5
15
SI7
FV20
5
CO7
LI 6
0
Legend: vr – Verrucano and Phyllads; g – gypsum; cc - Vugular Limestone Fm.; mac – Maiolica Fm.; Sc – Scaglia Toscana Fm.; mg - Macigno Fm.; fh – Flysh Helmintoides Fm
SI2
10
SI7
CO7
500
SO4 (meq/l)
TDS (ppm)
SI2
SI3
0
0
2
4
6
8 10 12 14 16 18 20
T°C
0
5
10
15
20
25
30
35
Ca (meq/l)
TYPE C WATERS: springs fed by deep hydrogeological structures made up of evaporitic and carbonate rocks.
MU 4 Na-Cl type spring
TDS = 16 g/l T = 16.5°C
In these aquifers, the morphology of the impermeable substratum
allows the waters to circulate at relatively large depth and to emerge
in the form of overflow and/or artesian thermo-mineral springs. The
hydrochemical facies of these waters varies from Na-HCO3 (PT1 and
PT21 springs) to Na-Cl-type (MU4, FV15, FV16 and FV22 springs), and
the outlet temperature range from 14.4 (FV15) to 26.9°C (FV22).
PT1 Na - HCO3 type spring
TDS = 388 mg/l T = 16.5°C
PT21 Na - HCO3 type spring
TDS = 628 mg/l T = 14.8°C
The FV22 Na-Cl type spring (EQUI TERME spring) was identified as a suitable site where install a continuous automatic monitoring station to identify
possible hydrogeochemical anomalies related to seismic activity.
CO2 anomaly
10 days before the M 3.7
Alpi Apuane earthquake
(August 27, 2004)
T anomaly
12 days before the M 5.9
Finale Emilia earthquake
(May 20, 2012)
The Authors thank the Seismic Service Office of Tuscany Region and all the municipalities of Lunigiana.
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