OICC Press Iranian Journal of Earth Sciences 2228-785X 17 2 2025 04 10 Improving the stability of the theta and normalized horizontal gradient filters by using the finite-difference vertical derivative 10.57647/j.ijes.2025.1702.15 EN Nguyen Ngoc Long Department of Geophysics, University of Science, Vietnam National University, Hanoi, Vietnam. & Geophysical Division, General Department of Geology and Minerals, Hanoi, Vietnam. https://orcid.org/0009-0008-8277-1373 Luan Thanh Pham Department of Geophysics, University of Science, Vietnam National University, Hanoi, Vietnam. https://orcid.org/0000-0002-5415-8001 Journal Article 2025 04 10 Estimating the boundaries of structures is a critical task in interpreting potential field data. In general, the enhancement filters based on derivatives are used to map these boundaries. The theta and normalized horizontal gradient are two popular filters used in mapping the structural edges, which can balance the signals with different amplitudes lying at different source depths beneath the subsurface. However, the use of vertical derivatives calculated from the traditional technique in these filters often amplifies noise. In this study, the performance of these filters has been improved using stable vertical derivatives from the finite-difference approach. The algorithms are tested on synthetic and real data from the Vredefort dome (South Africa). The findings from the synthetic examples show that finite-difference approach-based filters can provide stable results compared to the traditional calculations. The findings from the real application show that the finite-difference approach can provide a clearer image of the subsurface structures present underneath the study area.