INTERPRETATION COMPARISON USING MOVING AVERAGE AND SECOND ORDER POLYNOMIAL METHOD OF MERAPI’S SUBSURFACE

• Main Author: Shakina, Sophie
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/42358
• Institution: Institut Teknologi Bandung

The position of Indonesia at the meeting point of three huge plates which are Eurasian plate, Indo-Australia plate, and Pacific plate caused the formation of volcanoes series around it. Merapi Volcano is the most active volcano in Indonesia which surrounded by densely populated settlements with Yogyakarta as the closest city which is only less than 30 km from the summit. These conditions caused Merapi Volcano as a very hazardous mountain and included into the list of 16 Decade Volcanoes by The International Association of Volcanology and Chemistry of Earth’s Interior (IAVCEI). Therefore, research on subsurface structures, especially the structure of magma sources is important to understand the characteristics of Merapi Volcano. One of the methods that can be used is the gravity method which aim to model the structure of the magma source beneath the surface of Merapi Volcano. The data used in this study is a print complete Bouguer anomaly map of Merapi Volcano as result of gravity measurement in 2013. The map was converted into a digital map so that further processing can be done. Then the regional anomaly and residual anomaly separation process was carried out using moving average method and 2nd order polynomial method. Forward modeling in 2.5 D used ModelVision software based on geological information with background density value of 2.67 g/cc. The modeling results obtained showed a source of two basaltic andesite magma chambers. Layers of Merapi’s subsurface from old to young were lava flows of old Merapi, pyroclastic flow and lahar deposits, pyroclastic fall deposits, young (Post-Somma-Merapi) lava flows, and recent and mostly historical pyroclastic flow and lahar deposits. Sentolo Formation was suspected in the southern area. Kukusan Faults as normal fault were found in the southern and eastern area of the cross section. Differences in the models obtained from the two methods were the depth of the magma chamber, diameter of the magma chamber, distribution of layers, depth of the layers, and thickness of the layers of Merapi’s subsurface.