Investigation of Site Response in Xinjiang, Northwestern China, from S–Lg Fourier Amplitude Spectra

Abstract

ABSTRACT Abundant seismic waveforms have been collected in Xinjiang since 2007, following the deployment of permanent stations by the China National Seismic Network and the Xinjiang Seismic Network. We investigated regional attenuation of the S–Lg phase in the crustal waveguide and site response in Xinjiang using broadband recordings at 44 stations from 118 earthquakes with magnitudes of 4.4–7.0 occurring in Xinjiang and adjacent areas between January 2009 and February 2022. We used linear regression analysis of the Fourier acceleration amplitude spectra in 18 frequency bands from 0.1 to 24.86 Hz to estimate site response terms and distance-dependent anelastic attenuation quality factor Q in the crustal waveguide at regional distances. The regression site terms of stations located in the Tarim and Junggar Basins show significant amplification at low frequencies and strong attenuation at higher frequencies due to the presence of thick sedimentary deposits. We quantified the linear behavior of the logarithms of the high-frequency site terms versus frequency using the zero distance attenuation parameter κ0 (Anderson and Hough, 1984). A positive correlation was observed between κ0 and the thickness of the sedimentary layers in Xinjiang. We observed some consistent patterns in the behavior of the site response terms as a function of sediment thickness over the frequency range of 0.1–24.86 Hz. Linear functions of sediment thickness were used to model the site response in Xinjiang at each of the 18 frequencies. An alternative approach that adopted the κ0 model as a function of sediment thickness can be used to estimate site responses at high frequencies (≥5.66 Hz). The results of this study demonstrate the nature of site effects on earthquake ground motions caused by the thick sedimentary deposits in Xinjiang and provide a preliminary site response model as a function of sediment thickness for this region.