An Inversion of Lg-Wave Attenuation and Site Response in the North China Region

作者：Zhu, Xin-Yun^*; Chen, Yun-Tai

来源：Bulletin of the Seismological Society of America, 2012, 102(6): 2600-2610.

DOI：10.1785/0120110294

• FREQUENCY-DEPENDENT ATTENUATION
• GROUND-MOTION
• SEISMIC ATTENUATION
• EARTHQUAKE
• CODA
• MICROZONATION
• PROPAGATION
• VARIABILITY
• Q(LG)(-1)
• NEVADA

A joint inversion method for determining the Lg-wave attenuation along the propagation path and site response based on seismic spectral ratios was developed and applied to invert the Lg-wave attenuation gamma and site response in the North China region: gamma is related to the quality factor Q by gamma = pi f/UQ, where U is the velocity. Waveform data of 200 earthquakes during 2006-2008 with M-L 1.7-5.5 in the area of 38 degrees-41 degrees N, 114 degrees-120 degrees E were selected for this study. More than 1500 three-component records chosen from 81 stations on the basis of the signal-to-noise ratio were used in the inversion. The waveform data were processed in the frequency range of 1-6 Hz with an interval of 0.2 Hz. The results indicate that there is remarkable heterogeneity in Lg-wave attenuation in the study area. We divided the area into four regions according to the Lg-wave propagation paths. Lower gamma values are found in the tectonic mountain region, higher values occur in the tectonic basin region, and moderate gamma values are found for the propagation paths passing through both the mountain and basin regions.
On the vertical component, gamma was found to be frequency dependent and in the form gamma(f) = 0.0029f(0.4) (1/km) and gamma(f) 0/0070f(0.4) (1/km) for propagation paths in the mountain and basin regions, respectively, and gamma(f) = 0.0043f(0.22) (1/km) and gamma(f) = 0.0046f(0.24) (1/km) for paths passing through both mountain and basin regions with seismic ray direction from the mountain to the basin and vise versa, respectively. The absolute quality factor Q(0) ranges from 125 to 306.
The response of rock sites is smooth and flat and less than five at low frequency, while that for soil sites is higher than for rock sites. For soil sites, the amplification of low-frequency waves is higher than that for high-frequency waves. For both site response and attenuation, no significant differences were observed between different components.

• 出版日期2012-12
• 单位浙江省地震局; 中国地震局