1976年四川省松潘—平武地震前波速比的异常变化
ANOMALOUS VARIATIONS OF SEISMIC VELOCITY RATIO BEFORE THE SONG-PAN(松潘)—PINGWU(平武) EARTHQUAKE (M=7.2) OF 1976
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摘要: 利用四川及甘肃台网记录到的直达波到时资料,对1976年8月四川松潘—平武地震前的波速比异常变化作了初步探讨.所得结果表明,此次地震前波速比有明显的异常变化,Vp/Vs异常期及恢复期均较短,异常区在偏于主震震中南面的四川境内,其范围较大.Vp/Vs异常的某些特点显示出这次地震与1973年8月松潘—南坪6.5级地震既有密切关系,又有一定的区别.结合这一地区波速比异常变化的特点,本文对波速比回返问题和波速异常区叠加问题作了一些讨论.Abstract: Using the observational data of travel times of the direct seismic waves, recorded at the networks of seismic stations in Sichuan (四川) and Gansu (甘肃) Provinces, the preliminary studies of the velocity ratio anomaly before the Songpan-Pingwu earthquake in Sichuan Province of August, 1976 were made. The obtained results indicate that bofore this earthquake the anomalous variation of the velocity ratio was quite obvious, the durations of the Vp/Vs anomaly and its recovery were rather short. The anomalous region of very large extent was located to the south of the epicentral area of the main shock within Sichuan Province. Certain features of the Vp/Vs anomaly seem to show the connection and also difference between this earthquake and the Songpan-Nanping (Ms=6.5) of August, 1973. In consideration of the characteristics of the velocity ratio anomaly observed in this region, the related problems of its recovery and the superposition of the anomalous regions have been briefly discussed.
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