Some Characteristics of Seismicity Before Strong Earthquake Chi-Chi (MW = 7.6), 1999, Taiwan

The purpose of this paper is to perform an analysis with the features of the seismic regime on one of the strongest earthquakes in Taiwan during the twentieth century (Chi-Chi, Sep 21, 1999, Mw = 7.6). According to data, variations of three parameters of the seismic regime were studied retrospectively: total annual number of earthquakes N capital sigma in the range of magnitudes of M sub( L) = 2.5-5.5, total annual quantity of released seismic energy capital sigma E, J and angular coefficient b of graphs of recurrence of earthquakes. Two obvious sub-periods in course the seismic regime -- quiescence in 1990-1996 and activation in 1997-1999 - were chosen. The Chi-Chi earthquake 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).