Subsurface heat flux information is important in geothermal exploration. With the information, geophysicists can map exactly the thermal potential in a particular area. Based on the surface heat flux, inverse modeling produces the 1D subsurface heat flux distribution. However, inverse problems in the geothermal system are generally ill-posed. Small changes in the data can cause large changes in the solution and the solution may not be unique. To solve the mentioned non-linear and ill-posed equation above, Tikhonov regularization is a choice for stabilizing the inverse calculation. This paper demonstrates how Tikhonov regularization is useful to solve subsurface heat flux distribution both in the synthetic model and real model. Based on surface heat flux distribution from the direct problem, the preconditioned conjugate gradient algorithm calculates the subsurface heat flux. With the correct choice of the regularization parameter, the inverse model fits the initial model. For the testing purposes in real-world conditions, Chad sedimentary basin located in Chad and Nigeria is used as a model. A high geothermal gradient is found in this area. Therefore, geothermal explorations are on the rise recently. Its thermal conductivity, heat production, and stratigraphy data from previous researches provide information about the initial model. The heat flux curve generated from inversion matches the initial noisy model with the error of around 10−9 mW/m2. Therefore, to answer the increasing energy demand, this method can be highly applicable to future geothermal prospecting.

There are several manifestations of hot springs and mud pools in Gondang area, Bojonegoro, East Java, there were. This can be an indication of certain geological conditions. The description of these conditions can be done by measuring the geomagnetic method. A total geomagnetic anomaly has been generated through some geomagnetic values recorded in the region, which has been corrected using IGRF correction and diurnal correction. These steps were done to reduce external influences on the real value of the data. This research will use several variations of values in the Upward Continuation filter and one of them will be chosen to proceed as a model. Upward Continuation Filter is a process of transforming potential field data from a flat plane towards the higher plane. The purpose of this study is to compare the results of contour maps on several variations of the Upward Continuation value, to obtain the results of the separation of residual and regional anomalies using the Upward Continuation method, and to determine the value of the susceptibility distribution of inversion modeling in the Gondang region, Bojonegoro. Based on the results of data processing, it is known that the upward continuation value used is 100mdatum with a magnetic intensity value in the regional anomaly of 106.5 nT to 509.0. While the value of the residual anomaly is -232.1 nT to 159.4 nT. The 3D model was made using this residual anomaly which shows the low susceptibility distribution value in the range of -0.0298 to -0.0135 SI around the manifestation area, whereas the high susceptibility value has a value range of 0.0114 to 0.0466 SI interpreted as rock intrusion. Rock intrusion occurs within the area around the manifestation of mud pools.