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An earthquake catalog based on a unified magnitude scale is an important prerequisite for analyses of seismic activities and seismic hazards. To unify the magnitude scales of earthquakes in China’s seas and neighboring regions, we developed conversion relationships between surface- and body-wave magnitudes and the global centroid moment tensor (GCMT) and National Research Institute for Earth Science and Disaster Resilience (NIED) moment magnitudes for shallow and intermediate- and deep-focus earthquakes in China’s seas and adjacent areas. We employed data collected by the Chinese Earthquake Network Center, GCMT, and NIED for earthquakes of magnitude 4.5 and higher in China’s seas and neighboring regions from 1976 to 2018. We used the linear least squares regression method and the orthogonal regression method to fit the seismic data under different magnitude ranges and different focal depth ranges. The results provided empirical formulas to unify magnitude scales for the earthquakes in China’s seas and neighboring regions and also provided an important basis for seismic catalog integrity analyses and seismic activity studies for this area. The results are significant for seismic hazard analyses, seismic zoning, and mid- and long-term forecast analyses of seismic activities in the area.

In this study, we use a spatially smoothed seismicity procedure for seismic hazard analysis in North China seismic zone by establishing four spatially smoothed seismicity models according to the seismic catalogs of North China and calculating peak ground acceleration (PGA) values with 10% probability of exceedance in 50 years. The results show considerable differences between seismic hazards based on different models in certain areas, which is attributable to disparities in the seismicity levels of the four seismic models in those areas. In general, seismic hazard based on different models can be used as reference to evaluate uncertainty. In this paper, we also compare the mean PGA based on four spatially smoothed seismicity models with another PGA calculated using the zoning method based on surface seismic sources adopted for generating the Seismic Ground Motion Parameter Zonation Map of China, and find that the results of the two methods are largely similar, both of which can reflect the seismic hazard level of North China. However, there are differences at certain points, which are because the zoning approach adopts the same earthquake occurrence rate in the seismic source, while the spatially smoothed seismicity approach has different occurrence rates at different points. The discrepancies between the two can be attributed to differences in the principles adopted when potential seismic sources are classified. In particular, the PGA values of Beijing with 10% probability of exceedance in 50 years is 177.0cm/s2, 214.2 cm/s2, 252.8 cm/s2, and 187.5 cm/s2 in four spatial seismicity models, respectively. These PGA values are very important for evaluating the uncertainty of seismic hazard in Beijing. This study is an attempt to perform seismic hazard analysis using spatially smoothed seismicity models in China and recommends using this approach for areas where seismic sources are not clearly identified.

Taiyuan is a city in Shanxi Province, China, and possesses serious seismic hazard. In this study, we constructed a time-dependent seismic hazard model for Taiyuan and the surrounding area based on several major-earthquake seismogenic structures for which historical and paleoseismic event data were available. With the time-dependent model, we calculated the distribution of peak ground acceleration with 10% probability of exceedance in the next 50 years in Taiyuan and the surrounding area, and compared the results with those calculated using the time-independent model. The results showed that the entire area around Taiyuan has a higher seismic hazard with the time-dependent model than that with the time-independent model. The Jiaocheng and Hengshan faults have much higher seismic hazard. Applying the model only to Taiyuan showed that the city has higher seismic hazard with the time-dependent model than that with the time-independent model. In particular, in the western part of Taiyuan, the seismic hazard is quite high because of the proximity of the area to the Jiaocheng Fault.