Many islands in Indonesia are formed due to the lifting of the seafloor which forms limestone lithology and forms karst morphology. The karst region has a large freshwater potential that accumulates in the underground river system. The existence of an underground river system as a water reservoir is very important in fulfilling the needs of the community, especially in island countries such as Indonesia that have many karst regions. Research to map the position and distribution of underground rivers is carried out by applying geophysical methods. One of the geophysical methods applied is the microtremor method. The working principle of this method is the identification of underground rivers based on Particle Motion method and Time Frequency Analysis (TFA). That analysis resulted in the particles movement direction that perpendicular to the vibration source which is identified as the underground river. The existence of the underground river is then validated based on the TFA parameters of the underground river karst region. The results of the Particle Motion analysis at the research location show the character of the river flow pattern that has a Northeast-Southwestern orientation, and based on TFA there is amplitude continuity in the river flowed area with a frequency range of 4 - 5 Hz and an amplitude of 2,000 dB – 20,000 dB on component Z (vertical).

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Pringkuku is one of the transition areas where the morphology of karst began to develop toward the western part of Gunung Sewu Karst region. The purpose of this research is to identify the landform unit in Pringkuku's Karst as the result of geomorphological processes recorded by Landsat 8 image and SRTM image. The research was conducted by analyzing and dividing the landform units based on landform parameters such as flow patterns, slope forms, valley forms, and ridge patterns. Structural geology data such as a strike of joints and direct rock sampling are also used as the supporting data. The developing flow patterns are the multi-basinal and rectangular patterns in the western and eastern parts of the area respectively. Inferred from the analysis of joints pattern and stream lineament, the rectangular pattern is in direction NW-SE and NE-SW. The results of this research are two units of karst and structural landform, which are structural limestone hill unit in the eastern part of the area with 68.18% of spreading area of the total extent and conical limestone hill unit in western part of the area with spreading area of 31,82%.

This study was conducted to compare the performance of three different spatial analysis models: Inverse Distance Weighted (IDW), Ordinary Kriging,­­ and Regularized Spline interpolation technique to determine the best fit model representing Peak Ground Acceleration (PGA) in West Java Province, Indonesia. The three models are commonly used in spatial visualization, but have different calculation methods. The calculations were performed using available formulas while the spatial modeling was conducted using the algorithms in GIS software. Meanwhile, the accuracy of the spatial model and factual calculation was determined through the Root Mean Square Error (RMSE). The results showed differences for both spatial distribution and maximum and minimum values for each model. However, IDW was observed to be the model which approaches the factual value of the PGA calculation as indicated by its RMSE value of 0.772352 in comparison with the 7.169879 (Ordinary Kriging) and 1.140802 (Regularized Spline).