The main purpose of this work was to obtain, by means of gravity modelling, gravity reconstruction on the deepest portion (below 10 km) of the CROP 11 seismic line, which crosses the Apennine from Marina di Tarquinia (W) to Vasto (E), in order to achieve a reliable model of Central Italy deep structures.The applied methodology consists in a 2D trial-and-error gravity modelling of the deep structures, based on the regional component of the gravity anomaly only. The regional gravity anomaly along the profile has been obtained from 3D data, removing surficial gravity anomalies from Bouguer anomalies by means of the stripping off technique all over Central-Southern Italy. The 2D gravity modelling of the CROP11 seismic line is constrained by DSS data (Nicolich, 1981; Cassinis et al., 2003; Biella et al., 1997) and by deep reflection seismic data obtained along the CROP 11 line (Billi et al., 2001; Bigi et al., 2003; Parotto et al., 2004). The regional gravity anomaly trend of Central Italy is interpreted and its role as an independent constraint for the geological interpretation of the CROP 11 seismic line is also discussed.The model is carried out to a depth of 150 km taking into account constraints provided by seismic data and assigning the not-investigated portion of the crust and the upper mantle density values according to literature data. Then, modifications have been introduced in order to reach the best fitting between the two curves (observed gravity and calculated gravity).Given the main constraints, the best fit between calculated anomalies and the observed ones is obtained assigning a lower density to the western portion of the mantle (where high values of heat flow are observed). The westernmost part of the upper crust in the model also shows a slightly lower density. The gravity low in the Fucino area can be compensated with the combined effect of a regional deepening of both the main density (and velocity) discontinuities (such as the Moho and the top of the crystalline basement). The crust wedge below the Apennines shows an increasing density to a depth of 50 km. Nevertheless, the Moho depth provided by the CROP11 seismic data seems to be excessive, unless giving the lower crust the same density assigned to the mantle. Even the deepening of the crystalline basement top seems to be too much steep. Below 50 km no density contrast in comparison with mantle are expected. At greater depth (100-150 km) density contrast of about ±0,1 g/cm3 are possible without significantly affecting the gravity trend. On the CROP11 seismic line a “highly reflective structure” can be clearly detected in the Simbruini region at depth between 5 an 8 s TWT. This structure doesn’t have a marked gravity imprint and should consist of relatively “light” sedimentary units. As 3D regional gravity data were available, we were able to define the approximate shape, size and spatial distribution of this peculiar body, which constitutes the most evident feature of the entire seismic line. Summing up, the integrated (gravity and seismic) study of the CROP 11 profile reveals that the crystalline basement isn’t likely to be heavily involved in the deformation of the chain. However, ramp-and-flat deformations are present to a depth of 20 km. (*) This work has been carried out within the CROP 11 project (prof. M. Parotto co-ordinator).
Tiberti, M.M., Orlando, L. (2004). Deep structures of central Apennines from 3D and 2D gravity modelling along CROP11 seismic profile.
Deep structures of central Apennines from 3D and 2D gravity modelling along CROP11 seismic profile
TIBERTI, MARA MONICA;
2004-01-01
Abstract
The main purpose of this work was to obtain, by means of gravity modelling, gravity reconstruction on the deepest portion (below 10 km) of the CROP 11 seismic line, which crosses the Apennine from Marina di Tarquinia (W) to Vasto (E), in order to achieve a reliable model of Central Italy deep structures.The applied methodology consists in a 2D trial-and-error gravity modelling of the deep structures, based on the regional component of the gravity anomaly only. The regional gravity anomaly along the profile has been obtained from 3D data, removing surficial gravity anomalies from Bouguer anomalies by means of the stripping off technique all over Central-Southern Italy. The 2D gravity modelling of the CROP11 seismic line is constrained by DSS data (Nicolich, 1981; Cassinis et al., 2003; Biella et al., 1997) and by deep reflection seismic data obtained along the CROP 11 line (Billi et al., 2001; Bigi et al., 2003; Parotto et al., 2004). The regional gravity anomaly trend of Central Italy is interpreted and its role as an independent constraint for the geological interpretation of the CROP 11 seismic line is also discussed.The model is carried out to a depth of 150 km taking into account constraints provided by seismic data and assigning the not-investigated portion of the crust and the upper mantle density values according to literature data. Then, modifications have been introduced in order to reach the best fitting between the two curves (observed gravity and calculated gravity).Given the main constraints, the best fit between calculated anomalies and the observed ones is obtained assigning a lower density to the western portion of the mantle (where high values of heat flow are observed). The westernmost part of the upper crust in the model also shows a slightly lower density. The gravity low in the Fucino area can be compensated with the combined effect of a regional deepening of both the main density (and velocity) discontinuities (such as the Moho and the top of the crystalline basement). The crust wedge below the Apennines shows an increasing density to a depth of 50 km. Nevertheless, the Moho depth provided by the CROP11 seismic data seems to be excessive, unless giving the lower crust the same density assigned to the mantle. Even the deepening of the crystalline basement top seems to be too much steep. Below 50 km no density contrast in comparison with mantle are expected. At greater depth (100-150 km) density contrast of about ±0,1 g/cm3 are possible without significantly affecting the gravity trend. On the CROP11 seismic line a “highly reflective structure” can be clearly detected in the Simbruini region at depth between 5 an 8 s TWT. This structure doesn’t have a marked gravity imprint and should consist of relatively “light” sedimentary units. As 3D regional gravity data were available, we were able to define the approximate shape, size and spatial distribution of this peculiar body, which constitutes the most evident feature of the entire seismic line. Summing up, the integrated (gravity and seismic) study of the CROP 11 profile reveals that the crystalline basement isn’t likely to be heavily involved in the deformation of the chain. However, ramp-and-flat deformations are present to a depth of 20 km. (*) This work has been carried out within the CROP 11 project (prof. M. Parotto co-ordinator).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
