Ground-motion heterogeneity across four subdomains in Yunnan, China revealed by generalized spectral inversion

This study investigates regional ground-motion characteristics in Yunnan Province using 1,065 recordings from 60 small-to-moderate earthquakes (3.0 ≤ M_w ≤ 6.0) at 65 stations. A generalized inversion technique (GIT) using empirical reference site was applied to four tectonically distinct subregions (A-D). The inversion results reveal stress drops (Δσ) ranging from 0.3 to 7.34 MPa, with the highest averages in Regions C and D (2.21 MPa), followed by Region A (2.07 MPa) and Region B (1.16 MPa). Δσ shows no clear dependence on moment magnitude (M_w) or focal depth but correlates with surface heat flow. Reverse-faulting events exhibit a higher average Δσ than strike-slip and normal-faulting events. Quality factor models for the four study areas (A-D) are 118.41f ^0.691, 120.26f ^0.638, 77.20f ^0.598 and 72.19f ^0.861, respectively. The eastern regions (C and D) exhibit lower Q₀ and stronger S-wave attenuation, along with higher tectonic activity and lower surface heat flow. The predominant frequencies of average site amplification for GMX-A, GMX-B, GMX-C and GMX-D are 20.00 Hz, 10.83 Hz, 3.97 Hz, and 1.92 Hz, with corresponding amplification factors of 2.84, 4.31, 5.45, and 7.69. Finally, the inversion parameters were validated through stochastic finite-fault simulations of the 2009 M_S 6.3 Yao'an mainshock.