5:15 PM - 6:30 PM
[SVC28-P19] S-wave attenuation structure of Mt.Kirishima estimated using coda of S-wave
Keywords:Coda-wave, Attenuation structure
Mt.Kirishima is a volcanic group located on the border of Kagoshima prefecture and Miyazaki prefecture in Japan. Shinmoe-dake in the center of Mt.Kirishima has been active in 2011 and 2018. Therefore, it is important to estimate the underground structure of Mt.Kirishima in order to consider volcanic activities in the future.
When seismic waves go through the fluid such as a magma reservoir, the energy of waves is absorbed and scattered and the amplitude is attenuated. In this study, we estimated the underground structure of Mt.Kirishima by comparing the amplitudes of S-waves that normalized by coda-waves.
In this study, we used the data were obtained from 23 stations (Kyushu University, Tokyo University, JMA and NIED). We used seven earthquake events (M=1.3~2.3). These station and event were located around Mt.Kirishima. In the analysis, we used coda-normalization method which removes the source effect and site effect by amplitude of coda-wave. We used method (1) that image range of attenuation by comparing amplitude of S-wave and method (2) that estimate Q-value by ratio of root mean square amplitude of coda-wave (C_RMS) and root mean square amplitude of S-wave (S_RMS). In the method (1), we made amplitude of coda-wave recorded all station the same size that maximum amplitude of coda-wave for 3 seconds after the arrival time of coda-wave recorded at the station farthest from the hypocenter and we compared amplitude for 1 second after the arrival time of S-wave recorded at each station. In the method (2), we calculated C_RMS for 3 seconds after the arrival time of coda-waves (twice the travel time of S-wave) at each station and S_RMS for 1 second after the arrival time of S-waves at each station. We divided S_RMS calculated at each station by respective C_RMS and calculated the amplitude ratio. In the method (1), we connected hypocenter and station that amplitude of S-wave is smaller than standard on the map. We did the same procedure each events and imaged attenuation range where the lines overlapped. In the method (2), we divided the range where include hypocenters and stations into blocks in two dimensions and estimated Q-value in each blocks by least squares method.
In our results, attenuation range located south of Karakuni-dake in both methods. The hypocenters of volcanic earthquake distribute neighborhood of this attenuation range. Therefor we suggested there is heterogeneous structure related to volcanic activity at south of Karakuni-dake.
When seismic waves go through the fluid such as a magma reservoir, the energy of waves is absorbed and scattered and the amplitude is attenuated. In this study, we estimated the underground structure of Mt.Kirishima by comparing the amplitudes of S-waves that normalized by coda-waves.
In this study, we used the data were obtained from 23 stations (Kyushu University, Tokyo University, JMA and NIED). We used seven earthquake events (M=1.3~2.3). These station and event were located around Mt.Kirishima. In the analysis, we used coda-normalization method which removes the source effect and site effect by amplitude of coda-wave. We used method (1) that image range of attenuation by comparing amplitude of S-wave and method (2) that estimate Q-value by ratio of root mean square amplitude of coda-wave (C_RMS) and root mean square amplitude of S-wave (S_RMS). In the method (1), we made amplitude of coda-wave recorded all station the same size that maximum amplitude of coda-wave for 3 seconds after the arrival time of coda-wave recorded at the station farthest from the hypocenter and we compared amplitude for 1 second after the arrival time of S-wave recorded at each station. In the method (2), we calculated C_RMS for 3 seconds after the arrival time of coda-waves (twice the travel time of S-wave) at each station and S_RMS for 1 second after the arrival time of S-waves at each station. We divided S_RMS calculated at each station by respective C_RMS and calculated the amplitude ratio. In the method (1), we connected hypocenter and station that amplitude of S-wave is smaller than standard on the map. We did the same procedure each events and imaged attenuation range where the lines overlapped. In the method (2), we divided the range where include hypocenters and stations into blocks in two dimensions and estimated Q-value in each blocks by least squares method.
In our results, attenuation range located south of Karakuni-dake in both methods. The hypocenters of volcanic earthquake distribute neighborhood of this attenuation range. Therefor we suggested there is heterogeneous structure related to volcanic activity at south of Karakuni-dake.