Spatial distribution of time-independent seismicity in China

The seismicity in the territory of China, a seismotectonically complicated region, has been examined by using three complete samples of earthquakes wh ich occurred during the last two centuries (1800-1995). The b value of the Gutenberg-Richter relation was estimated by using this data sample. Taking into account the fact that the b value is spatially more stable than the a value, the b values were calculated at the nodes of a normal grid superposi ng on the entire area studied, and their distribution was examined. The res ults showed that the b value increases smoothly from 0.4 in inner-Mongolia to 0.8 in the east, south and southwest of China with higher values (b > 0. 8) in the Taiwan region. Furthermore, keeping fixed the obtained b values, the a value distribution was also examined. In order to display more detail ed information about the seismicity, smaller cell surface (10,000 km(2)) fo r the calculation of the a values was chosen. The mean return periods for d ifferent cutoff magnitudes were also calculated for each of these small cel ls. It was observed that the mean return periods are the shortest ones in C hina, which are 10 and 50 years for the magnitude larger than or equal to 6 .0 and 7.0, respectively.