Normalized Full Gradient Study of Bouguer Gravity Anomaly Profile of NorthWestern Iran

Document Type : Research Article


Department of Geophysics, Faculty of Earth Sciences, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan, Iran.


The potential field data like Gravity data, Magnetic data, Self-potential data, and other natural source data are accessible but hard to interpret and model. Numerous research presents ideas for modeling the potential data; however, they are mostly based on inverse or forward modeling needing a priori constraints and information. In complicated geology and tectonic setting, we do not have convenient access to a priori information to define the constraints. So, we must develop a pure geophysical interpretation method without geological constraints and minimum complexity. In this research, the Normalized Full Gradient’s ability to find the gravity anomaly model was studied. The Normalized Full Gradient method is an effective method for determining anomalous bodies, such as the distribution of oil and gas fields or structural boundaries. The Normalized Full Gradient method depends on the downward analytical continuation of normalized full gradient values of gravity data. Analytical continuation discriminates certain structural anomalies which cannot be distinguished in the observed gravity field. The Normalized Full Gradient of the gravity anomaly is often used rather than the gravity anomaly itself for detecting underground spaces because it is stable and indicates the locations of source bodies. The weakness of the Normalized Full Gradient is the 3D modeling limitation, as we can only calculate the 2D response in practice. On the other hand, the responses can not describe the negative and positive parts of the anomaly. But a unique advantage of the Normalized Full Gradient is, that it does not need the primary information for gravity data modeling. In this research, we used the Normalized Full Gradient for the large-scale Bouguer gravity anomaly interpretation. Bouguer gravity anomaly wavelengths contain information about density distributions of upper mantle and lithosphere structures. A gravity profile is most often a combination of relatively sharp anomalies that must be of shallow origin and very deep and large anomalies with a regional nature.
The study profile has a 400 (km) length from SW to NE of North Western Iran, and Sahand, North Tabriz Fault, and Sabalan are the most important structures in the study area. The Normalized Full Gradient synthetic model data study provides the opportunity for the real data recovered model judgment. So, we first showed the Normalized Full Gradient recovered model of the synthetic data test and then based on the resolution of the Normalized Full Gradient used, it provides the lithospheric density of North Western Iran. The result shows the low-density mantle wedge which is probably is beneath the North Tabriz Fault that is responsible for the formation of distinct lithosphere conditions. So, the wedge can explain the complicated tectonic setting of North Western Iran. The mantle wedge has more than 50 (km) wide and more than 40 (km) depth. seemingly, this mantle wedge directly affects the North Tabriz Fault, Sahand, and Sabalan in the shallower depth. The sharpest effect is for the North Tabriz Fault in the shallower part of the mantle wedge and following the shape of the wedge, we can see a sharper effect on the Sabalan in comparison with Sahand.


Main Subjects

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