宁波皎口地震近场速度特征研究

利用和达法和石川法对宁波皎口地震的资料进行处理，得到了各台站１９９３年和１９９４～１９９５年初两个时间段内的虚波速度和多台平均波速比。并得出如下结论：（１）樟水流动台１９９３年虚波速度值异常高，这主要是因为地震波特殊的传播路径以及传播介质在应力积累时产生大量微裂隙引起；而１９９４年后又呈大幅下降则主要是由于介质裂隙大量充水饱和后引起。（２）与樟水台同处近场的洪山和雪山两个流动台的虚波速度１９９３年虽也处于较高值，但与樟水台相比却明显要低，这是由于介质波速异常的方向性效应引起。（３）近场虚波速度明显高于远场虚波速度，多台波速比在４７级地震前处于中长期低值异常，而地震后回归正常。（４）近场速度特征可作为一项地震预报的追踪指标在皎口地震中应用，但还需进一步完善。

STUDY OF NEAR FIELD VELOCITY CHARACTERISTICS OF JIAOKOU EARTHQUAKE, NINGBO

Based on the analysis for the imaginary wave velocity and multistation average velocity ratio of 1993～1994 obtained with Ningbo Jiaokou earthquake data, the conclutions are as follows, (1)the imaginary wave velocity value of Zhangshui seismological station in 1973 was very high, which is caused by the special wave parth and medium porosity producted by stress accumulation, and then the value greatly decreased, because these porosities were fulled by water (2)The values of Hongshan and Xueshan stations of near field same as Zhangshui one were also higher in same period, but low than the latter, which is caused by medium directivity of wave velocity (3)The imaginary velocity of near field is high than far field, before M L4 7 earthquake multistation wave velocity ratio had been in the medium long term anomaly of low value, and after the earthquake becames normal (4)The application of near field characteristics as a prediction index to Jiaokou earthquake has also need to improve further