GNGTS 2015 - Atti del 34° Convegno Nazionale

A profile was extracted, running through the gravimetric low from the isostatic gravity map and then we upward continued the data at 81 different heights (from 0.001 to 0.081 km), in order to be able to build 55 vertical soundings of gravity. Therefore, we had 55 points with step size of 0.5 km, so getting 55 vertical soundings with 81 measures each. As we said previously, a boundary analysis was used to identify the horizontal dimensions of the sedimentary basin, in order to be able to build the theoretical volume needed for the inversion process, as shown in Bott (1962). At this point a theoretical volume was build of 199 layers and horizontal dimensions of 15 km along the direction of the strike and around 10 km in the direction orthogonal to it. The bottom of the theoretical volume was located at 5 km of depth, so that we could compare our results with those obtained by Phelps and Graham (2002). We used a density contrast range between -0.4 and 0.0001 g/cm 3 ; this information is derived from the apriori geological knowledge of the Frenchman Flat Basin. About the experimental error data, and following what synthetic cases shown, we used the lower value in the inversion process to obtained a good resolution of the inverse model. We have set this value equal to 10 -2 mGal. As we can see from the results (Fig. 3a) our estimates of depth at the deepest portion of the basin is around 2.4 km in agreement with the previous work. Even our estimates of density contrasts are consistent with the previous work. The particular asymmetric shape of this sedimentary basin is due to structural and tectonic origins. Note that the data are very well reproduced, as the fitting is very good, along all the profile. This result confirms what seen in analysis of synthetic data: even building a section by joining independent models related to several 1D inversions, we get a good data fitting along the entire profile. This means that the results obtained from a single 1D inversion are validated also along a profile, and opens new horizons to this kind of method. Conclusions. In this work we have presented a new inversion algorithm for potential field data, which consists in the inversion of vertical soundings of data collected at different altitudes. This is quite unusual for potential field data, but rather common for other geophysical methods, as geoelectrics, electromagnetics and seismics. Starting from the boundary analysis of the data map, we estimated the horizontal dimensions of the anomaly source. The inversion algorithm was tested on synthetic magnetic data, produced by a single buried body and on a real case, relative to gravity data referred to a sedimentary basin in Nevada, US. Fig. 3 – Results of the inversion process and the comparison between data and estimated data. GNGTS 2015 S essione 3.3 171