KOMBINASI MODEL MOGI DAN YOKOYAMA UNTUK ESTIMASI LOKASI SUMBER TEKANAN DAN VOLUME SUPLAI MAGMA GUNUNG MERAPI PERIODE TAHUN 2011-2013

Merapi volcano is a strato volcano located at the border of central Java Provinces and Yogyakarta Special Region, Indonesia. After a big eruption on 2010, Merapi has erupted with VEI (Volcano Explosion Index) I that are occurred on 15 July 2012, 22 July 2013 and 18 November 2013. The study of these characteristic eruptions is one indicator of volcano hazard mitigation, therefore this research have a purpose to modeling the location of the source of pressure and magma supply volume at Merapi Volcano in period 2011 to 2013. Three GPS (Global Positioning System) stations installed on December 2010 and five additional stations on June 2013. The GPS shown extension of the baselines beyond the summit crater, it means that Merapi has already entered into inflation process. The lengthening of the baselines from the summit to the navigation stations is about 5 mm to 15 mm and the displacement of GPS point varied in 2 mm to 50 mm. Estimation of the location of the pressure source and magma supply volume has been done using Mogi and Yokoyama models. The result shown the depth of pressure source before eruption on 15 July 2012 is 9.8 km and the magma supply volume about 45 million m3. Eruption 22 July 2013 and 18 November 2013 are controlled by the dual mechanism of the pressure source at 10.9 km and 4.5 km. Eruption 18 November 2013 controlled by the pressure source at 8.1 km and 2.9 km. Magma supply volume for these eruptions is about 10 million m3. Based on this study, it is known that eruptions are controlled by the pressure source from the internal activities of Merapi volcano