[STT48-P06] Surface displacements around Mt. Aso associated with the 2016 Kumamoto earthquake using interferometric SAR analysis
Keywords:InSAR
The 2016 Kumamoto earthquake sequence began on April 14th, 2016 with MJMA 6.5 along the Hinagu fault in Kyushu island, and the largest earthquake with MJMA 7.3 occurred on April 16th, 2016 along the Futagawa fault. The fault rupture terminated in the northwest of the Aso volcano, and the surface displacement up to about 90 cm in horizontal direction and about 20 cm in vertical direction has been observed during the 2016 Kumamoto earthquake.
It has been widely known that earthquake motions and stress variations of the crust influence volcanic activities and groundwater flow. And, previous studies have shown that the 2016 Kumamoto earthquake may have influenced the volcanic activity of Mt. Aso. Therefore, we estimated surface displacements before and after the 2016 Kumamoto earthquake using Interferometric synthetic aperture radar (InSAR) analysis. The method has an advantage that it does not need observation points on the ground and detailed spatial pattern of surface displacement can be clarified. The data used in this study are 20 PALSAR-2 data observed between February 9th, 2015 and June 12th, 2017.
As a result of the analysis, surface displacement of about 8 cm in the direction away from the satellite was observed within about 3km radius at the northwestern part of Aso Caldera between April 18th, 2016 (two days after the main shock of Kumamoto earthquake) and June 12th, 2017. Since this displacement has not been found by the InSAR analysis using data acquired before the 2016 Kumamoto earthquake and other previous researches, we interpreted that the displacement was associated with the 2016 Kumamoto earthquake. Furthermore, to estimate the source depth of the surface displacement, we applied the Markov chain monte carlo method to the spherical source model proposed by Mogi (1958), and estimated that the source depth is about 6.4 km. This depth and position almost agree with the upper end of the low resistivity area in Hata et al. (2016), which is expected to be a magma chamber or hydrothermal reservoir. Therefore, we inferred that the displacement is due to the migration of magma or other pore fluids. These results suggest that the volcanic activity of Mt. Aso was influenced by the 2016 Kumamoto earthquake.
It has been widely known that earthquake motions and stress variations of the crust influence volcanic activities and groundwater flow. And, previous studies have shown that the 2016 Kumamoto earthquake may have influenced the volcanic activity of Mt. Aso. Therefore, we estimated surface displacements before and after the 2016 Kumamoto earthquake using Interferometric synthetic aperture radar (InSAR) analysis. The method has an advantage that it does not need observation points on the ground and detailed spatial pattern of surface displacement can be clarified. The data used in this study are 20 PALSAR-2 data observed between February 9th, 2015 and June 12th, 2017.
As a result of the analysis, surface displacement of about 8 cm in the direction away from the satellite was observed within about 3km radius at the northwestern part of Aso Caldera between April 18th, 2016 (two days after the main shock of Kumamoto earthquake) and June 12th, 2017. Since this displacement has not been found by the InSAR analysis using data acquired before the 2016 Kumamoto earthquake and other previous researches, we interpreted that the displacement was associated with the 2016 Kumamoto earthquake. Furthermore, to estimate the source depth of the surface displacement, we applied the Markov chain monte carlo method to the spherical source model proposed by Mogi (1958), and estimated that the source depth is about 6.4 km. This depth and position almost agree with the upper end of the low resistivity area in Hata et al. (2016), which is expected to be a magma chamber or hydrothermal reservoir. Therefore, we inferred that the displacement is due to the migration of magma or other pore fluids. These results suggest that the volcanic activity of Mt. Aso was influenced by the 2016 Kumamoto earthquake.