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Mapping the depth to basement from gravity anomalies is an essential geophysical survey in sedimentary basins. We propose an iterative method to simultaneously estimate the basement relief, exponential density-depth model, and constant offset. The iterative process is achieved by applying the approximate invariance, which directly relates the basement depth to density parameters and constant offset. The method can be employed provided that there are a few known depth constraints. By testing the sediment and basement models, we find that the observation plane height and random noise of gravity anomalies have almost no impact on the stability of the method. However, the method is slightly affected by the number of constraints and is sensitive to the uncertainty of constraint depth. Finally, we successfully use the new method to map the depth to basement in the Pannonian basin using several depth constraints from drilling data and obtain the almost same density-depth model as that assumed based on drilling density. The method can be extended to recover the discontinuous basement relief and estimate other density-depth models, such as polynomial density function, once appropriate adjustments are made to the method.

We have established a workflow for a multiorder sequential joint inversion (MOSJI) of gravity and gravity gradients, that aims at modeling vertically stacked sources in various geological scenarios. We consider the joint inversion of the gravity data and one of the $h$ th-order derivatives of the gravity data. The first step involves separate inversions, which are fundamental to fully exploit the different wavelength-content of the two quantities to invert. The joint inversion is warranted by using the scheme of a sequential joint inversion with a cross-gradient constraint. The algorithm is able to exploit different types of a priori information, such as compactness and inhomogeneous model-weighting function. First, we test this approach on a realistic synthetic model from the SEg Advanced Modeling (SEAM) Phase I model, involving salt and mother salt structures. Then, we consider a synthetic model containing either shallower or deeper karst cavities. These tests produced a better modeling of both shallower and deeper sources, when compared to the separate unconstrained inversions. Thanks to these good results, we apply our method to a real case for cavity detection in Southern Spain. The method shows an accurate modeling of the expected sources. In all the aforementioned tests, we obtain a strong decrease of the cross-gradient values and a meaningful linearization in the scatter plots of physical parameters, both indicating the good performance of the joint inversion.

This study regards the assessment of surface gravity surveying for CO2 plume monitoring in the deep Johansen saline aquifer, a potential offshore site for CO2 geologic storage. We used the available benchmark model and geological information to simulate the injection and postinjection phases. We calculated the gravity response at the surface from the estimated models of reservoir density and saturation at different time intervals and for different injection rates. The forward calculation is achieved by assuming a tetrahedral mesh discretization such as to ensure an accurate and detailed reconstruction of the complex reservoir. The results show a gravity anomaly extending radially around the well position and reaching a peak of about $-15\,\,\mu $ Gal for an injection rate of 60 kg/s. During the postinjection period, the gravity maps clearly show an increase in brine saturation around the injection well and the migration of the CO2 plume toward shallower portions of the reservoir. We also show that time-lapse gravity data can be used to successfully estimate the CO2 stored mass by means of depth from extreme point (DEXP) multiscale analysis, even when the anomaly is incompletely defined due to a not proper areal coverage of the survey. The DEXP method has proven to be very stable with respect to noise and to be an efficient technique for simultaneously determining the CO2 plume depth, its geometrical features, and stored mass.

To investigate the crustal magnetic structure, it is important to assess the susceptibility and remanence properties of rocks and ores. In this paper, we propose a method to extract the contributions of induced and remanent magnetization from modeling of magnetic anomalies. We first estimate the direction of the total magnetization vector by studying the reduced‐to‐pole anomaly and its correlation with different magnitude magnetic transforms. Then we invert the magnetic data to obtain the volumetric distribution of the magnetization intensity. As the third step, based on a priori information about the Koenigsberger ratio derived from petrophysical measurements, we extract the distributions in the source volume of the induced and remanent magnetization intensities, based on a generalized relationship involving the total and remanent magnetizations, and the true susceptibility. In this way, we are able to produce separate maps of the anomaly fields attributed to the physical magnetic source parameters: remanent and induced magnetization. After validating the method with synthetic data, we analyze the data relative to the Mesozoic and Cenozoic igneous rocks in Yeshan region, eastern China. The analysis of the separated magnetization components reveals that the intrusion of dioritic and basaltic rocks occurred at different geological periods, and the basaltic rocks were magnetized by a reversed geomagnetic field. The uncertainty analysis shows that a larger Koenigsberger ratio is beneficial to extract more reliable remanence and susceptibility information. An inversion method of magnetic data in the presence of remanent magnetization is proposedInduced and remanent magnetizations are estimated for each block of the source domain, and corresponding magnetic anomalies are extractedYeshan region (eastern China) is studied, where Cenozoic basalts were formed during a period of reversed direction of the geomagnetic field

Laboratory measurement of density values of representative crystalline rocks of the Peloritani Mountains, southern Italy, constrain the interpretation of gravity data collected along a profile from the Tyrrhenian Sea to the Mt. Etna volcano. These data contribute detail to crustal models of this section of the southern Italy orogenic system. Regional gravity modeling, constrained by new petrophysical data, yields the following conclusions: (1) existence of a southward-transported nappe belt of a more internal domain; (2) interpretation of the Taormina tectonic line as the morphological evidence of the thrusting of the Kabilo-Calabrian terrane over the Apenninian-Maghrebian units; (3) reconstruction of the Moho geometry along the geotransect, confirming the abrupt change in depth just starting from the Tyrrhenian coastal zone of Sicily.

The estimation of the depth to the top and bottom of a magnetic source from magnetic data defines a nonlinear inverse problem, while the evaluation of the distribution of magnetization determines a linear inverse problem. In this paper, these interpretation problems are resolved in the continuous case of 21/2D magnetized bodies with lateral magnetization variations. A formulation of the magnetic problem accounting for different directions of remanent and total magnetization vectors and including a more general definition of apparent susceptibility is presented. Differences between 2D and 21/2D formulations are stressed, as regards the anomaly amplitude, shape and zero-level.

In this work, the crustal volume struck by the 2016–2017 seismic sequence in Central and Northern Apennines is investigated using constrained 3‐D inversion of the gravity anomalies. In order to focus on the area comprising the two mainshocks of the sequence, we perform a regional field removal on the data as a preprocessing step. This residual data set is then inverted into a 3‐D density contrast model. We perform a series of inversions to test different geological scenarios and parameters, with increasing complexity in the reference geometries. We first test a model comprising turbidites, carbonates and evaporites, and basement and then introduce a low‐density layer at the top of the basement. The geometries are obtained in agreement with the available geological and geophysical information in the area. We found that the density distribution with depth is compatible with previous models. Moreover, results support the hypothesis based on borehole evidence of a low‐density upper basement across the entire area, possibly consisting of low‐grade metamorphic rocks (phyllites). Finally, we compare our modeling results to the spatial distribution at depth of major seismic events between August and November 2016. These events appear to be concentrated within the denser units at both shallow and deep locations, while the deeper events often occur in a region of major density contrast corresponding to the top of the basement. We produce 3‐D inversions of gravity anomalies to investigate the relations between lithology changes and seismic eventsWe report a spatial relation between events distribution and density changes in the upper crustThe derived models support a layered basement limiting the depth propagation of seismic events