Some Characteristics of Seismicity Before Strong Earthquake

The purpose of this paper is an analysis of features of the seismic regime before one of the strongest earthquake Taiwan in the twentieth century (Chi-Chi, 21.09.1999, Mw = 7.6). According to data for 1990-1999 variations of three parameters of the seismic regime were studied retrospectively: total annual number of earthquakes NƩ in the range of magnitudes of ML = 2.5-5.5, total annual quantity of released seismic energy ƩE, J and angular coefficient b of graphs of recurrence of earthquakes. There were chosen two obvious sub-periods in course the seismic regime – quiescence in 1990-1996 and activation in 1997-1999. Earthquake of Chi-Chi occurred on a maximum of seismic activity. The prevalence of weak earthquakes during of preparation the Chi-Chi earthquake caused an overestimation of coefficient b graphs of earthquake recurrence (-1.16 on average)