GEOLOGICAL STRUCTURE AS A BASIS FOR ANALYSIS OF THE SUBSIDENCE POTENTIAL ZONING AT PINDUL AREAS, KARANGMOJO, GUNUNGKIDUL, YOGYAKARTA
Achmad Rodhi and Muhammad Ocky B. Nugroho
Geology Engineering Study Program , University of Pembangunan Nasional “Veteran” Yogyakarta
Abstract
Abstract Gunung Pindul, Bejiharjo, Karangmojo is a nature tourism area that utilizes the presence of underground caves and rivers. In the last 5 years this area often occurs flooding and subsidence. Geological Structure Mapping shows that there are 3 groups of burly and fault structures, most of which have undergone a process of dissolution to form diaclas, sinkhole, dolena, cave, polje and flow valleys on the surface and subsurface. Calcimetric analysis shows that the carbonate content of the Oyo Formation ranges from 76% to 92%. The etching analysis shows that the carbonates present are formed by calcite minerals. Petrophysical analysis shows the average percentage of rock pores ranging from 27.6% to 39.1%, with the lowest value around Watu Plengkung Kluwo and the highest around the Tanding Cave. Analysis of rock mechanics Unconfined Compressive Strength dry conditions obtained limestone shear angle values ranged from 10.9 MPa to 22.1 MPa with the lowest values around Tanding Cave and Suruh Cave while the highest value around Watu Plengkung, Kluwo. Unconfined Compressive Strength wet conditions show the value of limestone shear angle ranges from 5.6 MPa to 16.6 MPa with the lowest value around the Tanding Cave and Suruh Cave while the highest value in Beji Dolena. Weighting of subsidence susceptibility value using geological structure parameters, form of dissolution results, porosity percentage value, density value, shear angle value, obtained with an average score ranging from 14 to 34. The subsidence susceptibility zoning shows that the area around Pindul Cave, Tanding Cave, until Suruh Cave is a watchful zone for subsidence, especially in the rainy season.
Keywords: Structure, mapping, dissolution, subsidence, potential zoning
Topic: Geology