15:30 〜 17:00
[SVC28-P07] Source location of volcanic earthquakes at Sakurajima using CCF-based and amplitude source location methods
キーワード：Volcano Earthquake, Source location determination, CCF, ASL
Determining the source location of volcanic earthquakes is one of the most important aspects in volcanic activity monitoring. Nevertheless, it is hard to determine their hypocenters using P and S wave arrival times for seismic swarms consisting of continuous occurrence of Volcano Tectonic earthquakes (VTs), low-frequency earthquakes and/or sustained volcanic tremor. Some methods have been developed to overcome this problem, several method using, for example, cross-correlation analyses of seismic waves recorded at a seismic network (CCF-method, e.g., Droznin et al., 2015; Permana et al., 2020) and amplitude source location using the amplitude decay due to geometrical spreading and intrinsic attenuation (ASL, Battaglia and Aki, 2003) are presented. But, the evaluation of both methods is still limited.
In this study, we compare the hypocenters determined from CCF and ASL methods using the seismic swarm data at Sakurajima volcano. We use continuous seismic records of JMA stations for the period from 08h00m to 22h00m JST on August 15th, 2015. The vertical component records at 6 stations deployed on the Sakurajima volcano’s edifice are analyzed. Following Permana et al. (2020), we apply the CCF-based method by calculating interstation waveform correlations (CCFs). Since the peak of CCF represents the arrival time difference of a station pair, we compare the theoretical arrival time differences with the observed ones. We use the seismic velocity structure that is approximated from Miyamachi et al. (2013), in which S-wave velocity increases from 1.330 km/s at the ground surface with a vertical gradient of 0.775 s-1. For the ASL method, we first determine the site amplification factor using the coda wave normalization method (Phillips and Aki, 1986). Correcting the observed amplitude with the site amplification factors, we calculate the theoretical amplitudes by assuming an intrinsic attenuation factor of Q = 100 and S-wave velocity of 2 km/s.
The seismic waves at two frequency bands (4-8 Hz and 8-16 Hz) are analyzed. We apply the Source Scanning Algorithm (SSA) on a 3D grid with a spacing of 0.001° in latitude and longitude, and 0.1 km in depth, respectively.
We compare the 28 VT source locations estimated from CCF and ASL methods with the hypocenters determined from P- and S- wave arrival times. The difference (misfit) shows about 1 km mistfit in average both in lateral and vertical directions at 8 - 16 Hz frequency band. The results of CCF-based tend to show smaller misfits.
In this study, we compare the hypocenters determined from CCF and ASL methods using the seismic swarm data at Sakurajima volcano. We use continuous seismic records of JMA stations for the period from 08h00m to 22h00m JST on August 15th, 2015. The vertical component records at 6 stations deployed on the Sakurajima volcano’s edifice are analyzed. Following Permana et al. (2020), we apply the CCF-based method by calculating interstation waveform correlations (CCFs). Since the peak of CCF represents the arrival time difference of a station pair, we compare the theoretical arrival time differences with the observed ones. We use the seismic velocity structure that is approximated from Miyamachi et al. (2013), in which S-wave velocity increases from 1.330 km/s at the ground surface with a vertical gradient of 0.775 s-1. For the ASL method, we first determine the site amplification factor using the coda wave normalization method (Phillips and Aki, 1986). Correcting the observed amplitude with the site amplification factors, we calculate the theoretical amplitudes by assuming an intrinsic attenuation factor of Q = 100 and S-wave velocity of 2 km/s.
The seismic waves at two frequency bands (4-8 Hz and 8-16 Hz) are analyzed. We apply the Source Scanning Algorithm (SSA) on a 3D grid with a spacing of 0.001° in latitude and longitude, and 0.1 km in depth, respectively.
We compare the 28 VT source locations estimated from CCF and ASL methods with the hypocenters determined from P- and S- wave arrival times. The difference (misfit) shows about 1 km mistfit in average both in lateral and vertical directions at 8 - 16 Hz frequency band. The results of CCF-based tend to show smaller misfits.