摘要：Based on the measurement of the arrive time of maxima magnitude from band-pass filtering signals which were determined using a new Morlet wavelet multiple-filter method, we develop a method for measuring intrinsic and attenuative dispersion of the first cycle direct P-waves. We determine relative group delays of spectral components of direct P-waves for 984 ray paths from SML and ALS stations (CWBSN). Using continuous relaxation model, we deduce a new transfer function that relates intrinsic dispersion to attenuation. Based on the genetic algorithm(GA) , we put forward a new inversion procedure for determining   which is defined the flat part of quality factor   spectrum ,  and  parameters. Studied results indicate that:(1) The distribution of  values versus epicenter distance and depth show that   values linearly increase with increasing of epicenter distance and depth, and  values is clearly independent of earthquakes magnitude.(2)In the different depth ranges,  residual show no correlation with variations in epicenter distance. Some significant changes of   residual with time is likely caused by pre-seismic stress accumulation ,and associate with  fluid-filled higher density fractures rock volume in the source area of 1999 Chi-Chi Taiwan earthquake. We confirm that   residual with time anomaly appears about 2.5 years before the Chi-Chi earthquake. (3) A comparison of   residual for different depth range between SML and ALS stations show that the level of stress has vertical and lateral difference.(4)The area near observation station with both anomalously increasing and decreasing averaged   residual is likely  an unstable environment for future strong earthquake occurrence. This study  demonstrates the capability of direct P-waves dispersion for monitoring attenuation characteristics and its state changes  of anelastic medium of the Earth at short propagation distance using seismograms recorded from very small events.