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A significant number of geological profiles showed thick Quaternary and Neoproterozoic systems in the North China Plain. They also reveal basin structures from the Paleoproterozoic era. These structures extend over 100 km in length and span several kilometers in depth. In this paper, we establish a "two concave and one convex" basin tectonic model based on the latest data from urban active fault detection and basin tectonic patterns identified in North China. Using the finite difference method, we simulate and analyze the effects of their long-period ground shaking. The "vertical model" and "parallel model" display stronger amplification of long-period ground shaking than the regular model unaffected by submerged basin tectonics. The amplification varies across space and different time periods in both models. These suggest that the angle between the tectonic axis of the subduction basin and the rupture direction of the earthquake source may be a key factor in evaluating long-period ground shaking amplification in subduction basin structures. The analysis of spectral ratios indicates that subduction basin tectonics can amplify the peak ground shaking up to three times. The amplification could last for certain periods within a specific epicentral distance range. Such an amplification effect is significant for seismic hazard risk assessment and cannot be overlooked. This study provides a reference for future urban seismic hazard risk analysis in North China.

In this study, the strong ground motion of the Jiuzhaigou Ms7.0 earthquake, which occurred in northern Sichuan, China, was simulated based on the stochastic finite-fault method. The earthquake event was recorded by 66 strong ground-motion stations operated by the China Strong Motion Networks Center. We simulated 11 records selected within 200 km source-to-site distance. According to previous studies and empirical relationships, we estimated the region-specific input parameters. The zero-distance kappa filter obtained had a value of 0.0206 s. Two different source models were applied in this study: the random slip model and specified slip model. Using the stochastic finite-fault method, we simulated the PGA, Fourier spectrum and response spectrum at all stations. The stochastic simulated result based on the specified slip distribution models had no significant bias at most stations. Using a model with a random slip distribution, the simulated response spectra also matched the observed result, which indicated that the stochastic finite-fault method is not very sensitive to the input slip distributions and fault dimensions. We divided the study area into 1116 sites to simulate the spatial distribution of PGA based on the two models. The simulated maximum intensity of the epicentral area reached level IX, which was similar to the observed maximum intensity and indicated that the simulated result could be used in prediction of an imminent earthquake disaster. For future earthquake prediction, seismic hazards could even be estimated quickly without obtaining detailed information about the fault plane.

Graphical Abstract:

This paper proposes that on the basis of near-source saturation characteristic of ground motion, the peak ground motion acceleration and the acceleration response spectra of diffuse earthquakes affecting the nuclear facility site can be determined by the statistic method. In view of the problem of insufficient statistic samples due to fewer qualified strong earthquake records on the bedrock site, it also proposes that according to the features of ground motion response of the soil, the acceleration records on the soil site can be transformed into the equivalent acceleration records on rock site for a simultaneous statistic analysis together with the records on rock site. Consequently, we have obtained by this method the near-source peak acceleration and the acceleration response spectra of small and moderate earthquakes on the site that could meet the need of nuclear facility and made a comparative analysis to the results from relevant researches. This new method for determining diffuse earthquakes is only preliminarily verified in the paper and further research is needed for practical application.