MODELING OF SUB-SURVEY STRUCTURE BASED ON AEROGRAVITY DATA ON SULITI AND SUMANI SEGMENTS.

• Main Author: Qalbi Pebrian, Mutiara
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/70465
• Institution: Institut Teknologi Bandung

There are 3 active fault segments throughout the study area, the Sumani, Suliti segment, and the Siulak segment. This geographical condition makes West Sumatra an area prone to earthquakes, especially the area traversed by the active segment of the Sumatra fault. The application of the airborne-gravity method based on differences in rock density aims to analyze the subsurface structure of the study area. This airborne-gravity method can conduct research with a very wide area coverage, as well as a more effective time. So, this method is considered suitable for detecting the regional geology of the study area. The data used is the result of airborne gravity measurements from the Geospatial Information Agency (BIG). The quality of airborne gravity data is known using the cross-over method. This research is complemented by several supporting data, namely geological maps, land Bouguer anomaly maps from the Geological Agency, and earthquake occurrence data from the United States Geological Survey (USGS) and International Seismological Center (ISC). The Bouger airborne gravity anomaly data compared to the land anomaly from the Geological Agency shows almost the same anomaly pattern and a difference in anomaly values of ± 5-8 mGal, where this value is considered accurate enough for subsurface identification. There are 3 tracks for which 2D forward modeling is carried out, 2 tracks parallel to the Sumatra fault trending northwest-southeast and one cross-over track intersects all tracks in the southwest-northeast cross-over direction, the model consists of 2 depths, namely 40 km in general and 4 km for lithological depth in detail. The assumption of the locking area is based on the presence of an intrusive body that does not surface, possibly as an energy accumulation zone. Based on the earthquake data, it shows that there are 2 blocks with a recurring earthquake pattern, in the northern area of the Sumani segment and the southern part on the border of the Tutup and Siulak segments. Based on the 2D model, shows the subsurface structure and the presence of volcanoes between the segment boundaries, and the presence of magma chambers at a depth of 3 km – 18 km.