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In this paper, we collect and process free-field strong motion recordings from 70 earthquakes for 4.2 ≤ M W ≤ 7.9 at 0 < R rup < 300 km between 2008 and 2018 in the active tectonic regions of southwest China, and then establish a dataset containing 1324 average horizontal ground motion (ROTD50) and corresponding metadata such as parameters of the earthquake source, distance, and site. A new ground motion prediction equation (GMPE) for the average horizontal component of peak ground acceleration (PGA), peak ground velocity (PGV), and 5% damped acceleration response spectra at periods ranging from 0.033 to 8.0 s (SA (T = 0.033–8.0 s)) is introduced. This GMPE considers multiple influencing factors such as magnitude and distance saturation effect, geometric attenuation, style-of-faulting, hanging-wall effect, linear/nonlinear site response, and anelastic attenuation. The residual evaluation and median ground motion are presented. The predicted ground motions using the new GMPE are compared with predictions from the GMPE in western China and five NGA-West2 GMPEs, and the observed ground motions of strong earthquakes which occurred in southwest China. The results show that the proposed GMPE can better reflect the influence of the earthquake source characteristic, propagation media, site effect on the ground motion attenuation characteristic in southwest China, and works well versus independent strong motion data of earthquakes in southwest China, and well reflects the general feature of ground motions for the Wenchuan and Lushan earthquakes that is rich at short-period and weak at long-period. The new GMPE shows outstanding performance estimating the horizontal ground motion of the earthquakes in southwest China for M W 4.2–7.9 (related to style-of-faulting) and R rup = 10–200 km, at sites with V S30 = 140–1130 m/s. • A new GMPE considering multiple influencing factors in southwest China is presented. • Our GMPE can reflects the hanging-wall effect of the reverse and normal faulting. • Our GMPE can reflects captures the nonlinear mean effect of soil. • Our GMPE works well versus independent strong motion data in southwest China. [ABSTRACT FROM AUTHOR]

Lateral variations of shear wave velocity (V S) profile and time-averaged shear wave velocity in the upper 30 m (V S 30) are important indicators of site condition and significant contributors to uncertainty in earthquake ground motion and seismic hazards. Few previous studies involved in quantifying these lateral variations, especially at short distances, due to limited data at closely spaced sites. This study quantitatively investigated the lateral variation of V S profile and V S 30 over plain and piedmont terrains, focusing on short distances ranging from hundreds of meters to several kilometers. 2510 plain and 749 piedmont borehole profiles from the mainland China borehole profile database were employed to examine these variations using the variogram as the geo-statistics tool. The main findings include: 1) Over plain terrain, the variation in site conditions between sites does not significantly increase with separation distance within a certain range (typically from 1 km to 3–5 km). Over piedmont terrain, site condition variation steadily increases with distance. 2) The variation of site condition over piedmont terrain is higher than that over plain terrain. Nonetheless, for both terrains, the dispersion of site condition between sites at distance of <1 km is engineering negligible, and the correlation of site conditions between sites within 5 km remains strong; 3) For both terrains, the lateral variation of V S in deeper layers is higher than that in shallower layers. The study outcomes emphasize the importance of incorporating the information of nearby measurements in site condition estimations. The study outcomes can also be utilized in the optimization of borehole sampling design for microzonation projects and the evaluation of site condition dispersion at inferred sites. • Lateral variations of V S profile & V S 30 over plain & piedmont terrains were modeled. • The study focuses on lateral variations at short distance, down to < 1 km scale. • For gentle terrains, site conditions within short distance are strong correlated. • Plain has lower site condition variation than piedmont, with distinct properties. [ABSTRACT FROM AUTHOR]