滇西实验场两次中强地震前后尾波衰减的区域特征分析
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摘要
本文在地方震尾波散射理论模式的基础上，研究了１９９２年１２月发生在滇西地震预报实验场永胜期纳地区的两次Ｍｓ５．４，５．１地震前后的序列地震尾波振幅衰减率β和尾波Ｑｃ（－１）值随时间和空间变化的衰减特征。结果表明，尾波衰减率在空间分布上表现出明显的小区域范围的非均匀性，在主震震中附近（Δ＜５０ｋｍ）的近场区内，主震期间的β值是０．００７６ｓ（－１），相应的Ｑｃ（－１）值是０．００５６１余震期间的β值是０．０２０９５（－１），相应的Ｑｃ（－１）值是０．０１５３，主震前后Ｑｃ（－１）值的变化接近３倍。而在主震的外围地区（Δ＞５０ｋｍ），主震前的区域β值平均是０．０２３５ｓ（－１），Ｑｃ（－１）是０．０１５３，与余震期间的结果相接近，表明主震前后在外围地区的尾波衰减变化不明显。地震序列的Ｑｃ（－１）值主震前后的变化为上升（起伏变化较大）－下降到最低值（主震发生）－回升（起伏变化小）这样的演变过程，尾波振幅衰减率β和Ｑｃ（－１）所表现出的这种时空变化的非均匀性过程显示了具有明显前兆意义的变化。
In the light of the scattering theory model of coda origination from local earthquakes, we studied the attenuation characteristics of temporal and spatial changes of the rate β of coda amplitude and coda Qc(-1) values both before and after the Qina earthquakes(M5.4, M5.1) of December 1992 in West Yunnan Earthquake Prediction Study Area (WYEPSA). Results of the study shows the rate of coda amplitude attenuation demonstrates remarkable regional differences in the vicinity (Δ<50km) of the main shock area,during the main shock β=0. 0076s(-1) and Qc(-1)=0.0056; during the aftershock β=0. 0209s(-1) and Qc(-1)= 0.0153, Changes of mean Qc(-1) value is about 2. 0 times of the pre-and post-main events. Our result also get the regional mean β=0. 0235s(-1) and Qc(-1)=0. 0153, which showed teat the coda attenuation had no evident changes both before and after the main shock in the peripheral areas (Δ>50km) far away from the epicenter of the main shock. Changes process of Qc(-1) values of the seismic sequence with time demonstrated the foreshock increases-the main shock increases and the aftershock has gone up again, the changes of the clear precursory significances appeared inhomogereous change process of the spatial and temporal of the rate of coda amplitude attenuation β and Qc(-1).
In the light of the scattering theory model of coda origination from local earthquakes, we studied the attenuation characteristics of temporal and spatial changes of the rate β of coda amplitude and coda Qc(-1) values both before and after the Qina earthquakes(M5.4, M5.1) of December 1992 in West Yunnan Earthquake Prediction Study Area (WYEPSA). Results of the study shows the rate of coda amplitude attenuation demonstrates remarkable regional differences in the vicinity (Δ<50km) of the main shock area,during the main shock β=0. 0076s(-1) and Qc(-1)=0.0056; during the aftershock β=0. 0209s(-1) and Qc(-1)= 0.0153, Changes of mean Qc(-1) value is about 2. 0 times of the pre-and post-main events. Our result also get the regional mean β=0. 0235s(-1) and Qc(-1)=0. 0153, which showed teat the coda attenuation had no evident changes both before and after the main shock in the peripheral areas (Δ>50km) far away from the epicenter of the main shock. Changes process of Qc(-1) values of the seismic sequence with time demonstrated the foreshock increases-the main shock increases and the aftershock has gone up again, the changes of the clear precursory significances appeared inhomogereous change process of the spatial and temporal of the rate of coda amplitude attenuation β and Qc(-1).
引文
秦嘉政、阚荣举、王绍晋等，1992，滇西地区应力场和Q值的时空变化与地震前兆分析，地震，No．5．秦嘉政、阚荣举，1986，龙陵地震后区域Q值及平均由应力分布特征，地震学报，增刊．秦惠政，1988，云南地区尾波衰减及其与地震前兆的关系，地震研究，Vol．11，No．4．秦嘉政，1992，澜沧－耿马地震后尾波衰减的区域特征，地震学报，Vol．14，No．1．晏凤桐、莫洪进，1984，1982年剑川地震尾波，地震研究，Vol．7，No．2．葛焕称、倪岳伟等，1992，中国大陆区域Lg震级标度，地震学报，Vol．14，No．1．
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