Erupsion Center Determination of Ancient Volcano Based on Geomagnetic Method around Gunungkidul Area, Daerah Istimewa Yogyakarta, Indonesia

摘要

The center eruption of an ancient volcano eruption in Gunungkidul can be known from the field data like material products of ancient volcanic produced in the past, it is important to understand the ancient volcanic material elements by studying the geology of the region concerned, to prove the existence the center eruption of ancient volcano by using geomagnetic method. Field data that are found are as follows: there are existence of 1. Rocks of Pyroclastic flow 2. Pyroclastic fallout ("Pyroclastic Fall") like Tuff and lapilli tuff 3. breccia, tuffaceous sandstone and tuff breccia. 4. Pillow Lava in Berbah area the area that shows the lava sedimentation in the sea. 5. igneous rocks with scoria structure which is an volcanic extrusion in Parang Kusumo. 6. Lava which is the result of the eruption/volcanic eruptions. 7. Parangwedang hot springs near Parangtritis. Geomagnetic method mapped local disturbances in the Earth's magnetic field caused by variations in rock magnetism. This method is the oldest geophysical method. This method is often used for monitoring (monitoring) volcano The Results of this research is come from the interpretation of "Magblock" program, it can be concluded that in the past there is an ancient volcano eruption in the waterfront that has several tectonic processes of under Miocene. The eruption shape caldera with magma chamber's depth of 1 4. 3 km below the surface.