Pressure Source Model for Ground Inflation during the Periods of High Explosivity at Sakurajima Volcano in Japan – Combination Analysis of GPS, Tilt, and Strain Data –

Abstract:

During frequent vulcanian activity at the Minami-dake crater at Sakurajima during the period of 1974 – 1992, ground subsidence was observed and its pattern was modeled by two deflation sources: located in Aira caldera at a depth of about 10 km, about 6 km north from Minami-dake, and beneath Minami-dake at a depth of about 3 km [Eto, 1989]. Eruptive activities at Showa crater, about 500 m east of Minami-dake, since 2006 increased, accompanying ground inflation in October 2009 – May 2010 (2009 event) in contrast to the Minami-dake period. Similar inflation occurred in October 2011 – March 2012 (2011 event). In this study, we analyzed GPS, tilt and strain data synthetically to obtain pressure sources around Sakurajima during the periods of high explosivity with ground inflation.

We applied 3-pressure-source model to the deformation of 2009 and 2011 events. Main inflation source is located beneath Aira caldera at a depth of 9.6 km, similar to previous study. In Sakurajima, inflation pressure source is located beneath Kita-dake 1 km north of Minami-dake at a depth of 3.3 km (K-source), and deflation source is located beneath Minami-dake at a depth of 0.7 km (M-source). We estimated temporal change of volume of K- and M-sources fixing inflation rate of Aira source for 2011 event. Inflation rate of K-source increased in November 2011 and kept at a constant rate until January 2012. Deflation rate of M-source increased at the same time as inflation rate of K-source increased, and kept at a constant rate until March 2012. Amount of volume increase of K-source is nearly 20 times larger than that of volume decrease of M-source. Magma was thought to migrate from Aira source to K-source in November 2011 and continued until January 2012. Due to higher eruptive volume from Showa crater than migration of magma from K-source, M-source deflated slightly from late November 2011 to March 2012.