Analysis of Gravity on Altitude Changes in Gravity Micro Data Using Polynomial Equation Approach (Case Studies of Merapi and Kelud Volcanoes)

Analysis of gravity changes to altitude changes from gravity measurements at Merapi Volcano and Kelud Volcano was carried out to determine the characteristics of the two mountains based on the gravity method. Merapi Volcano and Kelud Volcano are two very active mountains in Indonesia and have different physiography, especially at the top of Kelud there is a crater filled with water. Repeated gravity surveys will be useful for studying deformation in volcanoes and providing information about changes in subsurface mass. The gravity data on Merapi Volcano is secondary data from BPPTKG (Research and Development Center for Geological Disaster Technology), and data on Kelud Volcano is obtained from the 2019 data collection survey. Volcanic monitoring using the gravity method is carried out by observing changes in gravity (�g) with changes in altitude (��) to study deformation in the volcano and providing information about changes in subsurface mass using a polynomial equation approach of �g to �� . The findings indicate that there was little variation in the gravity anomaly within Merapi Volcano between 2018 and 2019. The highest coefficient of determination, at 96%, was observed in the gravity anomaly data from inside the Kelud Volcano in 2019, after applying Bouguer corrections in the form of spherical effects. Additionally, the coefficients of the second and third order polynomials of the Merapi Volcano data had opposite signs to those of Kelud Volcano, suggesting that the internal source of the gravity anomaly within Merapi Volcano is distinct from that within Kelud Volcano.