11:15 〜 11:30
[SCG52-09] High-frequency later phases for intraslab earthquakes and attenuation in the mantle wedge beneath northeastern Japan
キーワード：Intraslab earthquakes、Later phases、Seismic attenuation、Scattering
For intraslab earthquakes occurred at depths of greater than 100 km beneath northeastern Japan, we found that arrival of peak amplitude in S wave remarkably delay in 8 Hz. Lag times of the peak amplitude from S-wave arrivals increases in seismograms recorded at backarc stations compared to those at forearc stations. In this study, we focus on the later phase observed in the high-frequency range and estimate their propagation paths by using a method based on the source-scanning algorithm [Kao and Shan, 2004]. Under the assumptions that the high-frequency later phase is a single scattered wave, we calculate lag time from direct S wave at a scattering point and stack observed S-wave amplitude for each scattering point as MS envelope of two horizontal components. Here, we take seismic attenuation along a scattered ray path into account as a weight for amplitude staking.
This analysis carried out in five frequency bands; 1-2, 2-4, 4-8, 8-16, and 16-32 Hz. In higher frequency bands (8-16 and 16-32 Hz), the later phase is obviously observed and often mark the maximum amplitude. In the frequency band, peak amplitude delays could be modeled as a wave detouring beneath the forearc region. These results suggest that the high-frequency later phases propagate avoid the mantle wedge which has strong attenuation, as discussed in Hasemi and Horiuchi [2010]. Additionally, the results suggest that the later phase may also be recorded in 4-8 Hz. In seismograms (4-8 Hz), the later phase seems to be recorded occasionally as the second peak of amplitude. Therefore, investigations of this frequency-dependence of the later phases and comparisons amplitude between the direct waves and the later phase would improve understandings of seismic attenuation in the mantle wedge and short wave-length structures beneath northeastern Japan.
This analysis carried out in five frequency bands; 1-2, 2-4, 4-8, 8-16, and 16-32 Hz. In higher frequency bands (8-16 and 16-32 Hz), the later phase is obviously observed and often mark the maximum amplitude. In the frequency band, peak amplitude delays could be modeled as a wave detouring beneath the forearc region. These results suggest that the high-frequency later phases propagate avoid the mantle wedge which has strong attenuation, as discussed in Hasemi and Horiuchi [2010]. Additionally, the results suggest that the later phase may also be recorded in 4-8 Hz. In seismograms (4-8 Hz), the later phase seems to be recorded occasionally as the second peak of amplitude. Therefore, investigations of this frequency-dependence of the later phases and comparisons amplitude between the direct waves and the later phase would improve understandings of seismic attenuation in the mantle wedge and short wave-length structures beneath northeastern Japan.