5:15 PM - 7:15 PM
[SVC32-P25] Analysis of crustal deformation associated with volcanic activity in 2019–2020 at Aso volcano
Keywords:Aso volcano, GPS, Crustal deformation
Estimating deformation sources and deformation rates associated with volcanic activity is crucial for understanding the mechanisms of volcanic eruptions and assessing the scale of eruption and sequence of eruptive style. At Aso Volcano, a phreatic eruption occurred in April 2019, followed by a series of magmatic eruptions from July 2019 to June 2020. This study focuses on this volcanic activity sequence, detecting volcanic crustal deformation during this period using GNSS observations and attempting to model it. Munekane and Kobayashi (2024) estimated the deformation rates at Aso Volcano during this period; however, they assumed only a spherical pressure source estimated by Nobile et al. (2017), without considering other possible deformation sources. Therefore, we divided the period into inflation and deflation phases and estimated the deformation source locations for each period using a single finite spherical source based on McTigue model.
We used GPS data from 108 stations across Kyushu, excluding the Sakurajima volcano area, operated by the Geospatial Information Authority of Japan (GSI), the National Research Institute for Earth Science and Disaster Resilience, and the Kyoto University Aso Volcanological Laboratory. Outlier removal and step correction were applied to all GPS data. Using data outside the Aso caldera, the contribution of tectonic deformation was modeled with a cubic function of latitude and longitude, which was then used to correct the tectonic influence within the caldera. The effects of the Bungo Channel slow slip event (2018-2019) were corrected using the fault model of Hirose et al. (2023). Additionally, the influences of the Kumamoto earthquake and annual/semiannual variations were modeled with logarithmic, exponential, and trigonometric functions, respectively, and subtracted to extract volcanic deformation at Aso Volcano.
The extracted volcanic deformation shows two distinct patterns: from December 2018 to July 2019, the deformation was characterized by horizontal expansion and vertical uplift centered around Kusasenri, while from July 2019 to June 2020, horizontal displacement was minimal, but vertical subsidence was observed, mainly in the northeastern part of the caldera. Based on these observations, we defined the former as Period 1 and the latter as Period 2 and performed an analysis using the crustal deformation software Pydeform (Munekane et al., 2016). Assuming a single McTigue model for each period, we estimated its location, radius, and volumetric change. As a result, for Period 1, we estimated a deformation source at a depth of 5.1 km directly beneath Kusasenri, with a radius of 80.5 m and a volumetric change of +1.3*10^6 m^3. For Period 2, we estimated a deformation source located approximately 3.1 km northeast of the Nakadake First Crater at a depth of 11.9 km, with a radius of 100.6 m and a volumetric change of -4.1*10^6 m^3. These results suggest that during Period 1 and Period 2, deformation occurred not only at the magma reservoir beneath Kusasenri but also at a deeper sill, as previously estimated by GSI (2004).
In the future, we will also analyze cases where two deformation sources are assumed.
Acknowledgments:
The GPS data used in this study were provided by the Geospatial Information Authority of Japan and the National Research Institute for Earth Science and Disaster Resilience. We thank Drs Hitoshi Hirose and Hiroshi Munekane for sharing their Bungo Channel SSE model and Pydeform code.
We used GPS data from 108 stations across Kyushu, excluding the Sakurajima volcano area, operated by the Geospatial Information Authority of Japan (GSI), the National Research Institute for Earth Science and Disaster Resilience, and the Kyoto University Aso Volcanological Laboratory. Outlier removal and step correction were applied to all GPS data. Using data outside the Aso caldera, the contribution of tectonic deformation was modeled with a cubic function of latitude and longitude, which was then used to correct the tectonic influence within the caldera. The effects of the Bungo Channel slow slip event (2018-2019) were corrected using the fault model of Hirose et al. (2023). Additionally, the influences of the Kumamoto earthquake and annual/semiannual variations were modeled with logarithmic, exponential, and trigonometric functions, respectively, and subtracted to extract volcanic deformation at Aso Volcano.
The extracted volcanic deformation shows two distinct patterns: from December 2018 to July 2019, the deformation was characterized by horizontal expansion and vertical uplift centered around Kusasenri, while from July 2019 to June 2020, horizontal displacement was minimal, but vertical subsidence was observed, mainly in the northeastern part of the caldera. Based on these observations, we defined the former as Period 1 and the latter as Period 2 and performed an analysis using the crustal deformation software Pydeform (Munekane et al., 2016). Assuming a single McTigue model for each period, we estimated its location, radius, and volumetric change. As a result, for Period 1, we estimated a deformation source at a depth of 5.1 km directly beneath Kusasenri, with a radius of 80.5 m and a volumetric change of +1.3*10^6 m^3. For Period 2, we estimated a deformation source located approximately 3.1 km northeast of the Nakadake First Crater at a depth of 11.9 km, with a radius of 100.6 m and a volumetric change of -4.1*10^6 m^3. These results suggest that during Period 1 and Period 2, deformation occurred not only at the magma reservoir beneath Kusasenri but also at a deeper sill, as previously estimated by GSI (2004).
In the future, we will also analyze cases where two deformation sources are assumed.
Acknowledgments:
The GPS data used in this study were provided by the Geospatial Information Authority of Japan and the National Research Institute for Earth Science and Disaster Resilience. We thank Drs Hitoshi Hirose and Hiroshi Munekane for sharing their Bungo Channel SSE model and Pydeform code.