Analysis of Rock Structures Based on Geoelectrical Resistivity Data of Wenner-Alpha Configuration Using Marquardt's Inversion Method

Information about subsurface structures is crucial to support work related to civil construction, one of which is the identification of basement rock for a preliminary research of laying the foundation of a building. Hard layers play an important role in maintaining the stability of the foundation from the effects of natural disasters (earthquakes) and land shifts caused by the exploitation of soil carrying capacity. One of the methods that can be used for identifying hard layers is geoelectrical resistivity method. This method processing uses Marquardt's inversion and damping factor functioning to stabilize the inversion process. The inversion process will be carried out when the value of RMSE between the synthetic resistivity data correlation of the initial estimation (starting model) and the field resistivity measurement data is over 10%. Error values of each line (L.1, L.2, and L.3) are 9.3%, 7.2 and 6.1%. Hard layers are identified as layers with resistivity values above 100 Ωm, namely tuffaceous sandstone, tuffaceous gravel, inserted breccia and limestone.