10:45 AM - 11:00 AM
[SSS11-06] Seismic attenuation around Mt. Fuji and Mt. Hakone: Implication for magma chambers
Keywords:seismic attenuation, magma chamber
First, we calculate a spectral amplitude ratio of P-wave (Aobs) for each waveform by divining the mean amplitude in a high-frequency band of 12-16 Hz by that in a low-frequency band of 1-4 Hz. We also calculate theoretical amplitude ratio (Acal) for any source-station pairs with a stress drop of 3 MPa and Q of 500 using the same frequency bands as the observations. We then define “Arat=Aobs/Acal” as a new indicator which quantitatively characterizes the degree of seismic attenuation. After calculating “Arat” of each waveform, we divide the target area into small blocks (~5 km by ~5 km by 5 km) and estimate seismic attenuation in each block.
The obtained results show that
1. There are highly attenuated zones beneath Mt. Fuji at depths greater than 20 km and around Mt. Hakone at depths of 0-5 km. They correspond to low-velocity anomalies that were detected in several previous studies.
2. There are highly attenuated zones that can be interpreted as magma chambers beneath Mt. Fuji at depths of 0-5 km and beneath Mt. Hakone at depths of 5-10 km.