The generalized inversion of S-wave amplitude spectra from the free-field strong motion recordings of the China National Strong Motion Observation Network System (NSMONS) are used to evaluate the site effects in the...The generalized inversion of S-wave amplitude spectra from the free-field strong motion recordings of the China National Strong Motion Observation Network System (NSMONS) are used to evaluate the site effects in the Wenchuan area. In this regard, a total of 602 recordings from 96 aftershocks of the Wenchuan earthquake with magnitudes of M3.7-M6.5 were selected as a dataset. These recordings were obtained from 28 stations at a hypocenter distance ranging from 30 km to 150 km. The inversion results have been verified as reliable by comparing the site response at station 62WUD using the Generalized Inversion Technique (GIT) and the Standard Spectral Ratio method (SSR). For all 28 stations, the site predominant frequency F and the average site amplification in different frequency bands of 1.0-5.0 Hz, 5.0-10.0 Hz and 1.0-10.0 Hz have been calculated based on the inversion results. Compared with the results from the horizontal-to-vertical spectral ratio (HVSR) method, it shows that the HVSR method can reasonably estimate the site predominant frequency but underestimates the site amplification. The linear fitting between the average site amplification for each frequency band and the V20 (the average uppermost-20 m shear wave velocity) shows good correlation. A distance measurement called the asperity distance DAspt is proposed to reasonably characterize the source-to-site distance for large earthquakes. Finally, the inversed site response is used to identify the soil nonlinearity in the main shock and aftershocks of Wenchuan earthquake. In ten of the 28 stations analyzed in the main shock, the soil behaved nonlinearly, where the ground motion level is apparently beyond a threshold ofPGA 〉 300 cm/s^2 or PGV 〉 20 cm/s, and only one station coded 51SFB has evidence of soil nonlinear behavior in the aftershocks.展开更多
An inversion method was applied to crustal earthquakes dataset to find S-wave attenuation characteristics beneath the Eastern Tohoku region of Japan. Accelerograms from 85 shallow crustal earthquakes up to 25 km depth...An inversion method was applied to crustal earthquakes dataset to find S-wave attenuation characteristics beneath the Eastern Tohoku region of Japan. Accelerograms from 85 shallow crustal earthquakes up to 25 km depth and magnitude range between 3.5 and 5.5 were analyzed to estimate the seismic quality factor Qs. A homogeneous attenuation model Qs for the wave propagation path was evaluated from spectral amplitudes, at 24 different frequencies between 0.5 and 20 Hz by using generalized inversion technique. To do this, non-parametric attenuation functions were calculated to observe spectral amplitude decay with hypocentral distance. Then, these functions were parameterized to estimate Qs. It was found that in Eastern Tohoku region, the Qs frequency dependence can be approximated with the function 33 f 1.22 within a frequency range between 0.5 and 20 Hz. However, the frequency dependence of Qs in the frequency range between 0.5 and 6 Hz is best approximated by Qs (f) = 36 f 0.94 showing relatively weaker frequency dependence as compared to the relation Qs (f) = 6 f^ 2.09 for the frequency range between 6 and 15 Hz. These results could be used to estimate source and site parameters for seismic hazard assessment in the region.展开更多
基金Nonprofit Industry Research Project of CEA under Grant No. 201208014National Natural Science Fund No. 51278473Environmental Protection Research Fund for Public Interest No. 201209040
摘要The generalized inversion of S-wave amplitude spectra from the free-field strong motion recordings of the China National Strong Motion Observation Network System (NSMONS) are used to evaluate the site effects in the Wenchuan area. In this regard, a total of 602 recordings from 96 aftershocks of the Wenchuan earthquake with magnitudes of M3.7-M6.5 were selected as a dataset. These recordings were obtained from 28 stations at a hypocenter distance ranging from 30 km to 150 km. The inversion results have been verified as reliable by comparing the site response at station 62WUD using the Generalized Inversion Technique (GIT) and the Standard Spectral Ratio method (SSR). For all 28 stations, the site predominant frequency F and the average site amplification in different frequency bands of 1.0-5.0 Hz, 5.0-10.0 Hz and 1.0-10.0 Hz have been calculated based on the inversion results. Compared with the results from the horizontal-to-vertical spectral ratio (HVSR) method, it shows that the HVSR method can reasonably estimate the site predominant frequency but underestimates the site amplification. The linear fitting between the average site amplification for each frequency band and the V20 (the average uppermost-20 m shear wave velocity) shows good correlation. A distance measurement called the asperity distance DAspt is proposed to reasonably characterize the source-to-site distance for large earthquakes. Finally, the inversed site response is used to identify the soil nonlinearity in the main shock and aftershocks of Wenchuan earthquake. In ten of the 28 stations analyzed in the main shock, the soil behaved nonlinearly, where the ground motion level is apparently beyond a threshold ofPGA 〉 300 cm/s^2 or PGV 〉 20 cm/s, and only one station coded 51SFB has evidence of soil nonlinear behavior in the aftershocks.
基金a part of author’s M.Sc Research under the project:‘‘Strengthening of Earthquake Engineering Center’’,funded by Higher Education Commission,Government of Pakistan
摘要An inversion method was applied to crustal earthquakes dataset to find S-wave attenuation characteristics beneath the Eastern Tohoku region of Japan. Accelerograms from 85 shallow crustal earthquakes up to 25 km depth and magnitude range between 3.5 and 5.5 were analyzed to estimate the seismic quality factor Qs. A homogeneous attenuation model Qs for the wave propagation path was evaluated from spectral amplitudes, at 24 different frequencies between 0.5 and 20 Hz by using generalized inversion technique. To do this, non-parametric attenuation functions were calculated to observe spectral amplitude decay with hypocentral distance. Then, these functions were parameterized to estimate Qs. It was found that in Eastern Tohoku region, the Qs frequency dependence can be approximated with the function 33 f 1.22 within a frequency range between 0.5 and 20 Hz. However, the frequency dependence of Qs in the frequency range between 0.5 and 6 Hz is best approximated by Qs (f) = 36 f 0.94 showing relatively weaker frequency dependence as compared to the relation Qs (f) = 6 f^ 2.09 for the frequency range between 6 and 15 Hz. These results could be used to estimate source and site parameters for seismic hazard assessment in the region.