Abstarct: Almost 70 percent of the Mazandaran province and many areas of urban and rural populations due to intense tectonic activities of Alborz region, is located on the faults or on the sidelines of the faults. The performance and structure of many faults in eastern part of central Alborz have been determined from numerous studies of structural geologists over the years in the region. Some of the results have been obtained baxsed on the surface studies. These surface studies need to be combined with the results obtained from subsurface studies. One ofn the cheap and powerful tools for mapping geological hidden (subsurface) structures on a large scale and to estimate the thickness, depth and spread of sedimentary basins, is the airborne aeromagnetic (aeromagnetic) method. Various geological units in an area often exhibit different magnetic properties. Due to this distinction in magnetic properties of the geological units, a correlation between the type of a geological unit and its magnetic response can be established. To determine the lateral and vertical extents of geological units from the magnetic data in a survey area, a number of filters for processing magnetic data can be used. Magnetic responses of deep anomalies are generally obtained by applying upward continuation filter on the magnetic data. If the upward continuation filter in contact between two laxyers having different magnetic properties is applied, the magnetic profiles with increasing height are displaced laterally. This displacement is carried out in the direction of the dip between the two laxyers. Combining the upward continuation filter results in the form of a three-component combination image, we can obtain the dips of geological laxyers from the magnetic data or map. In this study, the aeromagnetic data of eastern part of Mazandaran province have, first, been processed, and consequently, different geological formations have been distinguished. Then, the upward continuation filter has been applied, and as a result, different formations at different altitude levels have been determined. In addition, the dip angle and dip direction of faults (Including Khazar fault, north Alborz fault, Astaneh fault, Badeleh fault, Laleh-band fault, etc) in eastern part of Mazandaran province have been determined by calculating the boundary line of faults in different subsurface elevation level from the aeromagnetic data. In the next stage, these results have been combined with the results of the regional tectonic studies, and an analyis and assessment have been made on the combined results. Thes combined results well match the results of geological maps and studies. Basic approach for investigation of Khazar fault, due to covered areas by quaternary deposits and absence of the fault outcrop in some of areas in the region, is to use the subsurface exploration methods, and especially, high resolution geophysical methods. In this study, we have managed to detect the fault boundaries under the earth surface using the electrical resistivity and GPR methods, and then, forward and inverse modeling of the resistivity and GPR data. For this purpose, we initially design the resistivity and GPR survey lines perpendicular to the imaginary fault strike, and then, the obtained resistivity data have been modeled and inverted using the nonlinear least squares optimization method with the help of the RES2DINV software The obtained GPR data have been also modeled using the ReflexW software. Furthermore, the Khazar fault Synthetic resistivity model has been built in the Res2dmod software using the forward modeling method. The synthetic GPR model of the fault has also been built using the ReflexW software. Finally the geological model and especially the Khazar fault borders in Khalil Shahr region have been determined by comparing the forward and inverse modeling results, and also, by interpretation of the cross-sections obtained from the inversion process.