2003年イラン･バム地震(Mw＝6.5)の強震動

The acceleration waveforms of the mainshock of the 2006 Bam Earthquake, in southeast Iran (Mw 6.5) have been analyzed to derive several characteristics of strong ground motion. The near field effect of the main shock caused a huge maximum acceleration of about 1G at the Bam station. Waveform analysis of this record shows a big effect of directivity with a strong motion in the fault normal direction. The fault normal component of the near field record shows a maximum displacement of about 30 cm. This effect is also shown when comparing the response spectrum of fault normal and fault parallel components of strong motion. The fault normal response spectrum shows a spectral displacement almost 2 times that of the parallel component, especially for periods greater than 1 s. The attenuation relations derived for both vertical and horizontal components have a very good correlation. Comparisons of the attenuation relation of the Bam earthquake with predictive attenuation relations in other regions (North of Iran, Turkey, and Japan) show a higher PGA gradient of decay in the Bam earthquake surrounding area. Calculations of duration of strong ground motion records show that up to 100km strong motion duration increases with distance, and, after that, duration decreases. This could be explained by adding upper crust reflected waves up to 100 km, a weakening of wave amplitude, and decreasing total arrived energy at each station with distance increasing beyond 100 km. From a calculation of maximum displacements at all triggered stations the propagation pattern is also derived

Strong ground motions of the 2003 Bam Earthquake, Southeast of Iran (Mw 6.5)

The acceleration waveforms of the mainshock of the 2006 Bam Earthquake, in southeast Iran (Mw 6.5) have been analyzed to derive several characteristics of strong ground motion. The near field effect of the main shock caused a huge maximum acceleration of about 1G at the Bam station. Waveform analysis of this record shows a big effect of directivity with a strong motion in the fault normal direction. The fault normal component of the near field record shows a maximum displacement of about 30 cm. This effect is also shown when comparing the response spectrum of fault normal and fault parallel components of strong motion. The fault normal response spectrum shows a spectral displacement almost 2 times that of the parallel component, especially for periods greater than 1 s. The attenuation relations derived for both vertical and horizontal components have a very good correlation. Comparisons of the attenuation relation of the Bam earthquake with predictive attenuation relations in other regions (North of Iran, Turkey, and Japan) show a higher PGA gradient of decay in the Bam earthquake surrounding area. Calculations of duration of strong ground motion records show that up to 100km strong motion duration increases with distance, and, after that, duration decreases. This could be explained by adding upper crust reflected waves up to 100 km, a weakening of wave amplitude, and decreasing total arrived energy at each station with distance increasing beyond 100 km. From a calculation of maximum displacements at all triggered stations the propagation pattern is also derived