[S-VC32] Active Volcanism

[SVC32-10] Characteristics of seismicity in and around active volcanoes in Japan

*Takeshi Nishimura¹ (1.Department of Geophysics, Graduate School of Science, Tohoku University)

Keywords:seismicity, D90, b-value, Fractal Dimension

Seismicity in and around active volcanoes is used to understand volcanic processes and activity. Temporal changes sometimes enable us to predict the eruption and/or the transition of volcanic/eruptive activities. Such seismicity has often been investigated at active volcanoes where significant changes in volcanic activity have been observed and/or volcanic eruptions have occurred. On the other hand, Japan has 111 active volcanoes, most of which are not active but are expected to erupt in future. Therefore, the present study systematically examines some basic characteristics of seismicity, such as the b-value of Gutenberg-Richter’s law and fractal dimension D. In addition, we estimate radial variation in D90 (the depth above which 90% of the earthquakes occur) from the summit, which is considered to be related to heat flow.
The results using JMA unified earthquake catalog from 2003 to 2023 show that b-values and fractal dimension D indicate no significant lateral variation down to 16 km from the summit. This suggests no significant difference in heterogeneity and/or stress conditions between in and around active volcanoes. D90 is small beneath the summit, increases with distance, and merges with the peripheral regions. D90 at the summit is ca. 7 km on average, and that beneath the peripheral regions is ca. 12-13 km. The transition horizontal distance ranges from 5 to 55 km with a peak at 5-15 km.