Publication Date:
2017-04-04
Description:
A controlled source audiofrequency magnetotelluric (CSAMT) survey has been undertaken in
the Pantano di San Gregorio Magno faulted basin, an earthquake prone area of Southern
Apennines in Italy. A dataset from 11 soundings, distributed along a nearly N-S 780 m long
profile, was acquired in the basin’s easternmost area, where the fewest data are available as to
the faulting shallow features. A preliminary skew analysis allowed a prevailing 2D nature of
the dataset to be ascertained. Then, using a single-site multi-frequency approach, Dantzig’s
simplex algorithm was introduced for the first time to estimate the CSAMT decomposition
parameters. The simplex algorithm, freely available online, proved to be fast and efficient. By
this approach, the TM and TE mode field diagrams were obtained and a N35!W ± 10! 2D
strike mean direction was estimated along the profile, in substantial agreement with the fault
traces within the basin. A 2D inversion of the apparent resistivity and phase curves at seven
almost noise-free sites distributed along the central portion of the profile was finally
elaborated, reinforced by a sensitivity analysis, which allowed the best resolved portion of the
model to be imaged from the first few meters of depth down to a mean depth of 300 m b.g.l.
From the inverted section, the following features have been outlined: (i) a cover layer with
resistivity in the range 3–30 ! m ascribed to the Quaternary lacustrine clayey deposits filling
the basin, down to an average depth of about 35 m b.g.l., underlain by a structure with
resistivity over 50 ! m up to about 600 ! m, ascribed to the Mesozoic carbonate bedrock;
(ii) a system of two normal faults within the carbonate basement, extending down to the
maximum best resolved depth of the order of 300 m b.g.l.; (iii) two wedge-shaped domains
separating the opposite blocks of the faults with resistivity ranging between 30 ! m and 50 !
m and horizontal extent of the order of some tens of metres, likely filled with lacustrine
sediments and embedded fine gravels.
Description:
Published
Description:
120–130
Description:
2.6. TTC - Laboratorio di gravimetria, magnetismo ed elettromagnetismo in aree attive
Description:
JCR Journal
Description:
reserved
Keywords:
CSAMT method
;
2D data processing and inversion
;
Southern Apennines chain
;
faulted depression
;
04. Solid Earth::04.02. Exploration geophysics::04.02.04. Magnetic and electrical methods
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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