p value in Omori's law and the b value in G-R relation are probably the most broadly accepted statistics in seismicity study. In this paper, we focused on the p and b values of two great earthquake sequences occurred in China, the 1999 Chi-Chi Mw7.6 earthquake and the 2008Wenchuan Ms8.0 earthquake. We calculated both values of each sequence, analyzed some statistic characters of these values, compared them, and drafted some features based on the calculation and comparison. By comparing the temporal variation of bvalue with the moment cumulating, we found that almost each inflexion on the cumulative moment curve corresponded to a sharp hop on the temporal fluctuation of b value. This might due to the fact that b value indicates stress condition in the same region. Earthquake releases strain energy, causing stress to change. As a result, the temporal undulation of b value may indicate the variation of stress condition. Furthermore, we attempted to explain the different aftershock distribution pattern of the two earthquakes. The primary determinants, referring to geological data, may be the trend and pattern of the fault system and stress state in the aftershock district.
The Sep 21, 1999 Chi-Chi, Taiwan, earthquake (Mw7.6) is the largest inland earthquake that occurred in Taiwan in the 20th century, while the May 12, 2008 Wenchuan earthquake (Ms8.0) is the most affected earthquake to China in the beginning of the 21st century. In this study, we concentrated on two statistic values p value and b value, whose variation respectively relates to the stress and energy changes during aftershock period. We found some proof to define the relations. Another focus was the spatial distribution difference between the Chi-Chi and the Wenchuan aftershock sequences. By geological data, we found that different stress conditions might be the main reason.
