5:15 PM - 7:15 PM
[SVC32-P10] Detection of deep expansion source of Mt. Zao by removing postseismic deformation
Keywords:GNSS, postseismic deformation, Mt. Zao , expansion source
Active volcanoes in the Tohoku region may be experiencing mid-term to long-term crustal deformation phenomena that have not been detected due to the postseismic deformation of the 2011 Tohoku Pacific Ocean Earthquake. One such volcano is Mt. Zao.
Mt. Zao has recently been experiencing more volcanic activity than before. GNSS observations detected the inflation event from 2014 to 2015. Although no other inflation event was detected, seismic activity increased since around 2013. Therefore, in this study, we aimed to detect mid-term to long-term crustal deformation phenomena that have not been detected by removing the postseismic deformation of the 2011 Tohoku Pacific Ocean Earthquake from the GNSS data.
The data used in this study are the daily coordinate value F5 solution from the Geospatial Information Authority of Japan and the coordinate value of Bodaira, which is observed by the Japan Meteorological Agency for volcanic monitoring. We compared two methods to remove the postseismic deformation of the 2011 Tohoku Pacific Ocean Earthquake from the GNSS data. One method is a time function model by Tobita (2016). Parameters for two logarithmic functions, an exponential function, and a stationary velocity term were estimated from the displacement time series of each GNSS station and removed. The other method is a spatial function model by Munekane (2021). We assumed that GNSS station more than 20 km away from Okama (the assumed crater of Mt. Zao), are not affected by volcanic crustal deformation. We calculated the parameters of the spatial pattern of the monthly postseismic deformation from the monthly displacements of eight surrounding GNSS stations, and removed the postseismic deformation from GNSS data within 20 km of Okama.
As a result, we were able to detect inflation events from January 2013 to March 2014, July 2014 to September 2015, and March 2017 to October 2017 (spatial function model only). Of these, the inflation event from July 2014 to September 2015 was pointed out previously, while the other two were newly detected in this study. We estimated the source (spherical pressure source model) for these expansion events. However, the time function model still contains effects that are common to all GNSS station. Therefore, we simultaneously estimated the translational components and the parameters of the spherical pressure source model. As a result, the source was estimated at the northeast direction of Okama for all events. The depth of the source was estimated to be around 10 km, but this could not be sufficiently constrained because it varies greatly depending on the amount of volumetric expansion. This is thought to be due to the small number of GNSS station used to estimate the deformation amount.
Mt. Zao has recently been experiencing more volcanic activity than before. GNSS observations detected the inflation event from 2014 to 2015. Although no other inflation event was detected, seismic activity increased since around 2013. Therefore, in this study, we aimed to detect mid-term to long-term crustal deformation phenomena that have not been detected by removing the postseismic deformation of the 2011 Tohoku Pacific Ocean Earthquake from the GNSS data.
The data used in this study are the daily coordinate value F5 solution from the Geospatial Information Authority of Japan and the coordinate value of Bodaira, which is observed by the Japan Meteorological Agency for volcanic monitoring. We compared two methods to remove the postseismic deformation of the 2011 Tohoku Pacific Ocean Earthquake from the GNSS data. One method is a time function model by Tobita (2016). Parameters for two logarithmic functions, an exponential function, and a stationary velocity term were estimated from the displacement time series of each GNSS station and removed. The other method is a spatial function model by Munekane (2021). We assumed that GNSS station more than 20 km away from Okama (the assumed crater of Mt. Zao), are not affected by volcanic crustal deformation. We calculated the parameters of the spatial pattern of the monthly postseismic deformation from the monthly displacements of eight surrounding GNSS stations, and removed the postseismic deformation from GNSS data within 20 km of Okama.
As a result, we were able to detect inflation events from January 2013 to March 2014, July 2014 to September 2015, and March 2017 to October 2017 (spatial function model only). Of these, the inflation event from July 2014 to September 2015 was pointed out previously, while the other two were newly detected in this study. We estimated the source (spherical pressure source model) for these expansion events. However, the time function model still contains effects that are common to all GNSS station. Therefore, we simultaneously estimated the translational components and the parameters of the spherical pressure source model. As a result, the source was estimated at the northeast direction of Okama for all events. The depth of the source was estimated to be around 10 km, but this could not be sufficiently constrained because it varies greatly depending on the amount of volumetric expansion. This is thought to be due to the small number of GNSS station used to estimate the deformation amount.