Movement Detection of Sermo Dam Control Point Based on GNSS Observation Data in 2016 - 2017

There is a fault under the Sermo Dam. It's known based on the Geology Map of Yogyakarta in 1995. It is a normal fault, which there is a fault up on one side, and fault down in another party. The fault divides Sermo Dam in the center. The direction is from Sermo Dam straight ahead to the southeast to Pengasih. There is no information about the level of fault activity in Sermo Dam, includes the effect of fault to the Sermo Dam deformation. In the previous research built many control points in the Sermo Dam and measured it yearly. This study measured the five Makro control points in the year 2016 and 2017. The measurement using relative-static GNSS observation method. The duration of observation is for four days with the sampling rate 15 seconds. The processing of GNSS observation data uses GAMIT/GLOBK version 10.61. This processing aims to get coordinates value and to determine the movement velocity. In the GNSS data processing used seven IGS stations as reference points. These are COCO, DARW, GUUG, IISC, KARR, LHAZ, and PIMO. The IGS stations located around the observation area. The study result shows that there is a movement at all Makro control points. The movement velocity is between 0.02-0.05 m/year on the X-axis, 0.008-0.037 m/year on the Y-axis, and 0.002-0.024 m/year on the Z-axis. The horizontal movement directions are to the east and the southeast. It was similar to the movement direction of Sundaland block which is a part of Eurasia plate. In the vertical movement, MAK1 and MAK5 points indicate that the control point is moving up. But at other points (MAK2, MAK3, MAK4) have negative values that or show the control point is moving down. In the locations distributions, MAK1 and MAK2 located on the left side of the fault. MAK2, MAK3, and MAK4 situated on the right side of the fault. The differences sign in Y-axis indicates there is a vertical deformation. Due to the fault movement under the Sermo Dam.