Adopting normalized full gradient method for regional‐scale gravity modelling: A case study for Northwestern Iran

Abstract The normalized full gradient was developed to determine anomalous bodies, such as oil and gas fields or simple geological structures studies. We believe that even in complicated geology, normalized full gradient is practical. We introduce data preprocessing and use step‐by‐step simple‐to‐complicated synthetic tests to develop previous researchers’ ideas for regional‐scale gravity modelling. One of the most important steps of the normalized full gradient is the determination of the N optimum value. We found that prevalent methods such as the standard spectral or maxima method are feasible in simple structures only. So, we have suggested the imaging criteria routine for complicated cases. We trace maximum normalized full gradient responses to detect the normalized full gradient responses at the increasing harmonic numbers as the transition of the extensive part of the anomaly to the sharp part of that. With imaging criteria for the determination of N optimum values, the complicated synthetic test results show the success of the normalized full gradient to understand complicated gravity signals. In the real case, we have studied the Northwestern Iran normalized full gradient model of the Bouguer ground gravity data beneath the seismic profile and prepared a P receiver function depth section to uncover the geometry of the Moho boundary and important interfaces in the crust. We suggest the inferred synthetic model from the Bouguer ground gravity anomaly and P receiver function depth section to normalized full gradient trustworthy test in real cases. According to the synthetic test results, we understand the frame of the normalized full gradient responses in the semi‐real case and truthful responses in the real case. Along with this, we study the second ground gravity profile of Northwestern Iran in a good resolution to uncover the deeper structures. The real case results show the possibility of Moho offset and thinning lithosphere beneath the North Tabriz Fault lithospheric boundary, the possible source of Sahand volcanic centre at the west side of the Moho offset beneath North Tabriz Fault, the deep root of the Sabalan volcanic centre in the lower crust and the lithospheric and asthenospheric wedge with the density contrast beneath Sahand–Sabalan volcanic centres. One of the most important results of our study is the lithosphere–asthenosphere boundary offset and stepped Moho possibility beneath the Talesh Mts next to the South Caspian Basin boundary.