Land Subsidence Identification in Gas Exploitation Area in Sidoarjo, East Java Using Integrated Geodetic Methods

Land subsidence around the gas exploitation area in Sidoarjo Regency, East Java Province, Indonesia, located in the northeastern part of Java Island, has been detected since 2006. This subsidence occurs not only in the vicinity of the Sidoarjo mud eruption but also extends to the Wunut and Tanggulangin areas, where several gas production wells are located. This study identifies land subsidence using integrated geodetic methods, including InSAR (PS-InSAR and SBAS), GNSS, and levelling observations. InSAR provides spatially continuous measurements from satellite radar imagery, while GNSS and levelling observations at control points are used to evaluate and interpret the detected deformation. GNSS provides point-based three-dimensional displacement, whereas levelling offers high-accuracy vertical displacement information. The results show notable differences between the InSAR approaches. PS-InSAR indicates a maximum subsidence of −249.4 mm, with a velocity of −41.01 mm/year, whereas SBAS yields a maximum subsidence of −510.43 mm and a velocity of −86.08 mm/year. GNSS observations indicate an average subsidence rate of −52.2 mm/year during 2020–2022, while levelling results show an average subsidence rate of −205.4 mm/year during 2022–2023. These differences are primarily attributed to variations in spatial sampling, temporal coverage, and the measurement characteristics of each method, particularly under rural and wetland conditions with limited persistent scatterers. Overall, the integration of InSAR, GNSS, and levelling data provides a more comprehensive interpretation of land subsidence and highlights the importance of considering method-dependent uncertainties when comparing deformation results from different geodetic techniques.