5:15 PM - 6:45 PM
[U15-P40] Attenuation Characteristics of Strong Ground Motions due to the 2024 Noto Peninsula Earthquake
Keywords:The 2024 Noto Peninsula Earthquake, Strong Ground Motion, Attenuation Characteristics, Quaternary Volcanoes
Strong ground motions were observed widely centered around Chubu region during the 2024 Noto peninsula earthquake. In this region high frequency wave propagation is complicated due to low-Q zones around active volcanoes densely distributed in the area.
To reveal the effect of those low-Q zones on attenuation characteristics of high frequency waves in the region, bedrock motions (BRM) converted from the ground motions (OBS) observed at K-NET and KiK-net sites in the region during the event were analyzed. The converted BRM data were used to estimate a BRM amplitude BRM(f) and an attenuation coefficient b(f) at query points arranged in the region, by a least square method weighting nearby observation sites at frequency bands of 0.4, 0.7, 1.3, 2.2, 4, 7, 13, 22 Hz. The query points were arranged at 0.04 degN and 0.055 degE intervals in north latitude and in east longitude respectively, to image fine distribution maps of BRM(f) and b(f) data in the area.
The resultant map of BRM(f) ( Fig.1 ) showed skewed isoseismal distribution, indicating complicated damping structure in the region. Although the map of b(f) ( Fig.2 ) showed quite inhomogeneous damping distribution, it is found that high damping zones indicated by large b(f) values were consistent with distributions of quaternary volcanoes.
Furthermore, other nine crust events with magnitudes larger than 6 in Japan Sea side of Honshu were analyzed in the same way, and distribution of attenuation coefficients averaged over results of ten events were estimated to obtain more stabilized and finer map, and distribution of Q values were evaluated assuming S wave velocity of 3.5 km/s. Also, low-Q zone in the results ( Fig.3 ) corresponded to distributions of quaternary volcanoes. Q(f) in the vicinity of these active volcanoes ( Fig.4) were lower about one standard deviation than average Q(f) of the whole region.
To reveal the effect of those low-Q zones on attenuation characteristics of high frequency waves in the region, bedrock motions (BRM) converted from the ground motions (OBS) observed at K-NET and KiK-net sites in the region during the event were analyzed. The converted BRM data were used to estimate a BRM amplitude BRM(f) and an attenuation coefficient b(f) at query points arranged in the region, by a least square method weighting nearby observation sites at frequency bands of 0.4, 0.7, 1.3, 2.2, 4, 7, 13, 22 Hz. The query points were arranged at 0.04 degN and 0.055 degE intervals in north latitude and in east longitude respectively, to image fine distribution maps of BRM(f) and b(f) data in the area.
The resultant map of BRM(f) ( Fig.1 ) showed skewed isoseismal distribution, indicating complicated damping structure in the region. Although the map of b(f) ( Fig.2 ) showed quite inhomogeneous damping distribution, it is found that high damping zones indicated by large b(f) values were consistent with distributions of quaternary volcanoes.
Furthermore, other nine crust events with magnitudes larger than 6 in Japan Sea side of Honshu were analyzed in the same way, and distribution of attenuation coefficients averaged over results of ten events were estimated to obtain more stabilized and finer map, and distribution of Q values were evaluated assuming S wave velocity of 3.5 km/s. Also, low-Q zone in the results ( Fig.3 ) corresponded to distributions of quaternary volcanoes. Q(f) in the vicinity of these active volcanoes ( Fig.4) were lower about one standard deviation than average Q(f) of the whole region.