Impact of local site conditions on seismic hazard in Xinjiang region

The Xinjiang region in northwestern China is characterized by complex geological structures and frequent seismic activity. The spatial distribution of ground motion intensity and seismic damage to engineering structures in this area is critically governed by local site conditions. To systematically evaluate site effects on ground motion parameter distribution, this study investigates the influence of overlying soil layers on regional seismic hazard using spatial distributions of shear-wave velocity （v_S30）and site classification data.

Adopting the three-level potential seismic source division from Seismic ground motion parameter zonation map of China （5th Generation） and integrating Bindi et al’s regional ground motion attenuation model, we performed probabilistic seismic hazard analysis （PSHA）using the OpenQuake engine. Our analysis compares seismic hazard parameters—including peak ground acceleration （PGA） and spectral accelerations （S_a） at 0.2 s, 0.5 s, and 1.0 s periods—between reference rock sites （Class Ⅰ₁, v_S30＝742 m/s）and actual site conditions. Results are presented for three 50-year exceedance probabilities: 63%（frequent）, 10%（design basis）, and 2%（maximum considered）. Spatial distribution maps were generated, and site-specific adjustment coefficients were statistically derived through comparative analysis of Site Classes Ⅱ/Ⅲ against Class Ⅰ₁.

Key findings reveal:

1） OpenQuake-derived hazard estimates align with Fifth-Generation Map trends, showing significant PGA/S_a amplification in soft soil basins （Tarim and Junggar）but attenuation in hard rock regions （Altai/Tianshan/Kunlun mountains）;

2） Spectral adjustment coefficients for Classes Ⅱ/Ⅲ exhibit period-dependent variation, peaking at about 0.4 s with maximum values of 1.87 （Class Ⅱ）and 3.15 （Class Ⅲ）under design-level conditions;

3） Site Class Ⅲ demonstrates far higher amplification effects relative to the reference rock Site Class Ⅰ ₁ than dose Site Class Ⅱ. Furthermore, the adjustment coefficients for both site classes show minimal variation across different exceedance probabilities, indicating that regional seismic hazard levels exert negligible influence on site-specific amplification phenomena;

4） Compared with national averages, Xinjiang-specific adjustment coefficients show reduced values for Class Ⅰ ₁ and elevated values for Class Ⅲ, suggesting potential over-conservatism in rock site design and under-estimation for soft soils when applying national standards.

This study establishes a framework integrating regional site models, attenuation relationships, and probabilistic analysis to characterize site-dependent ground motion variability in Xinjiang. Our results provide critical insights for incorporating site-specific effects into seismic fortification strategies in Xinjiang, particularly for infrastructure resilience in basin regions with thick soil sediments.