丽江、宁蒗强震的波速比时空演化图象和数值分析
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摘要
通过对１９９６年２月３日滇西北丽江７０级地震前波速比时空演化图象的动态追踪，同时对比了相距９０ｋｍ的１９７６年１１月７日、１２月１３日宁蒗６７、６４级地震。发现，不同作者在不同时间研究的滇西北地区这两次重复发生的强震在孕育过程中波速比的时空演化图象十分相似：强震前５～７年，强震孕震区出现波速比高值异常区；强震前３～４年，孕震区的波速比大面积低值异常；强震前１～２年左右，孕震区再次出现范围略小的波速比高值异常区；强震发生在波速比低值异常区包围的两次高值异常区重叠部位。两次强震前滇西北波速比月均值均持续低值异常数年后，在震前１年左右出现明显的偏离平均值，当高、低值异常均趋于正常时，强震的孕育进入短临阶段。进一步研究波速比高、低值异常区的数值分布，显示出：第一次高值异常区中波速比最大的地震发生在异常区的边缘；低值异常区和第二次高值异常区中波速比最小和最大的地震发生在异常区内。这些波速比最大、最小的地震距主震的距离不超过６０ｋｍ。
Time sapce evolution pattern of the wave velocity ratio before Lijiang earthquakewith M =7 0 on February 3,1996 was traced,at the same time,Ninglang M =6 7,6 4 earthquakes on November 7,December 13,1976, 90km away from the Lijiang had been compared.It was discovered that this pattern was very similar,and it was studied by different authors at different times before two strong earthquakes reoccurred in northwestern Yunnan: In seismogenic areas of strong earthquakes, the wave velocity ratios of the high value anomalies appeared 5～7 years before the event, the low value in large area 3～4 years before, and the high value in smaller area again one year before;strong earthquakes occurred in overlapping place of two high value areas that surrounded by the low value area.The mouthly mean values in northwestern Yunnan before two earthquakes that were continued in low value for several years,they deviated from the balanced state evidently one yeara before the event,when high and low value returned to the normal,the seismic preparation entered the short and immediately stage. The numerical analysis of high and low value showed as follows:the wave velocity ratio of maximum earthquake in first high value anomalous area occurred on the margin of anomaly region; in low and second high value areas,the wave velocity ratio of minimum and maximum earthquakes occurred inside of areas,those earthquakes appeared within 60km from the main earthquakes.
Time sapce evolution pattern of the wave velocity ratio before Lijiang earthquakewith M =7 0 on February 3,1996 was traced,at the same time,Ninglang M =6 7,6 4 earthquakes on November 7,December 13,1976, 90km away from the Lijiang had been compared.It was discovered that this pattern was very similar,and it was studied by different authors at different times before two strong earthquakes reoccurred in northwestern Yunnan: In seismogenic areas of strong earthquakes, the wave velocity ratios of the high value anomalies appeared 5～7 years before the event, the low value in large area 3～4 years before, and the high value in smaller area again one year before;strong earthquakes occurred in overlapping place of two high value areas that surrounded by the low value area.The mouthly mean values in northwestern Yunnan before two earthquakes that were continued in low value for several years,they deviated from the balanced state evidently one yeara before the event,when high and low value returned to the normal,the seismic preparation entered the short and immediately stage. The numerical analysis of high and low value showed as follows:the wave velocity ratio of maximum earthquake in first high value anomalous area occurred on the margin of anomaly region; in low and second high value areas,the wave velocity ratio of minimum and maximum earthquakes occurred inside of areas,those earthquakes appeared within 60km from the main earthquakes.
引文
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