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This paper analyzed the strong motion characteristics based on 86 three-component strong motion records of the MW 6.6 Luding earthquake. Additionally, the factors that influence the variation in ground motion for three earthquakes with similar magnitude in Sichuan Province were investigated. The analysis result indicates a strong correlation between the observed ground motion parameters and the distribution of published Modified Mercalli Intensity. The residual analysis reveals that the spectral accelerations at periods 0.1–10.0 s are amplified to 0.0798–0.3057 times the mean level in the rupture forward direction and weakened to 0.0738–0.2831 times the mean level in the rupture backward direction. The maximum pulse direction recorded by the 51LDJ station is N6°E, aligning with the vertical fault direction. The velocity pulses has distinct bidirectional pulses in the waveforms, with a PGV of 37.0 cm/s. The source effect of the strike-slip MW 6.6 Luding and MW 6.5 Jiuzhaigou earthquakes on ground motion is relatively less significant compared to the average level of mainshocks in southwest China. However, the thrust-fault MW 6.7 Lushan earthquake exhibits a stronger source effect on ground motion during short and medium periods, but a weaker source effect during long periods when compared to the average level. The anelastic attenuation of the Longmenshan, Xianshuihe, and Huya fault zones in Sichuan exhibits significant regional variation and periodic correlation. This phenomenon is closely linked to the regional tectonic background variations and the heterogeneity of crustal structure within the area. [ABSTRACT FROM AUTHOR]

We compare and analyze the consistency of observed acceleration and velocity data recorded by accelerometer and seismometer simultaneously in five aspects: time series, 5% damped response spectra, the variation and distribution characteristics of peak value ratios and spectral acceleration ratios, and correlation analysis. The results show that these two have good consistency, especially in medium-frequency bands and medium- and far-fields. In the research dataset of ground motion prediction equations (GMPEs), we propose the weight ratios of the observed acceleration and velocity records and verify that the empirical weighted ratios are reasonable and reliable and applicable to southwest China. [ABSTRACT FROM AUTHOR]

[Display omitted] • The new ground motion prediction model can capture the nonlinear mean effect of soils in the capital circle region of China. • Our ground motion prediction model can predict the observed ground motions in this region. • The regional variability of ground motion is caused by the difference in anelastic attenuation and site response. • The regional differences in the anelastic attenuation at rock sites decrease with increasing periods. • GMPMs developed using data from different magnitude ranges within the same region should not be used interchangeably. Based on strong motion and seismic velocity records from small-to-moderate earthquakes in the capital circle region of China, we developed a new ground motion prediction model (GMPM) that incorporates magnitude, geometric attenuation, anelastic attenuation, and linear/nonlinear site response terms. The GMPM was subjected to evaluation through residual analysis. We compared the median predictions of the GMPM with those of two commonly used local GMPMs, as well as the observed ground motions in this region. Furthermore, we conducted an investigation into the differences between the GMPM and four NGA-West2 models. Additionally, we explored certain model parameters that could potentially explain these differences. The results indicate that the GMPM effectively captures the magnitude-dependent attenuation and nonlinear average effect of soil sites. The GMPM demonstrates the capability to predict horizontal peak ground acceleration (PGA), peak ground velocity (PGV), and spectral acceleration (SA (T = 0.01–3.0 s)). The model is applicable for surface wave magnitudes (M S = 3.1–5.1), hypocentral distances (R hyp = 10–200 km), and V S30 = 103–1070 m/s in the capital circle region of China. There are significant differences in anelastic attenuation at rock sites between southern California and the capital circle region of China. These differences decrease with increasing periods and largely diminish in far sources and soil sites. This is primarily because the effect of anelastic attenuation is neutralized by the greater site amplification of ground motion in southern California, especially over medium and long periods. The difference in ground motion observed in small-to-moderate earthquakes across different regions is predominantly influenced by long-distance attenuation and dissimilarities in site responses. [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]