Subsurface identification as preliminary survey of geo-ecotourism cave development using Electrical Tomography Resistivity (ERT) method in Tritis Cave and its surroundings

Tritis Cave is a karst cave, located in the Gunungsewu Geopark area, Tanjungsari District, Gunungkidul Regency, DIY. This cave will be developed into a geo-ecotourism of the cave, which in practice requires an adequate supply of clean water. The availability of clean water in Tritis Cave and its surroundings is a major problem because it is influenced by the karst hydrogeological system which is characterized by the scarcity of surface water and the subsurface flow network. This makes it difficult to determine the location of groundwater sources. For this reason, it is necessary to investigate the subsurface using the dipole-dipole ERT method. ERT method acquisition with a=20 m and n=1 to 8 along 400 m has been carried out . The depth obtained from the 2D inversion of ERT data is 45 m. Interpretation is carried out on the results of 2D inversion of ERT data and is integrated with the results of surface geological mapping. The results obtained indicate the presence of a sedimentary basin at 100 m to 220 m, with a depth of 40 m. there is a crack in the bottom of the basin that connected to underground cave. The depth of the cave cannot be known from the results of the ERT which was carried out because it has a low penetration depth.