有关1997年11月8日西藏玛尼地震震级的讨论

Discussion on the Magnitude of the Earthquake Occurring at Mani,Tibet on November 8,1997

１９９７年１１月８日在我国西藏西北部玛尼地区发生了一次强震。中国台网所定震级为ＭＳ７．４，而ＰＤＥ给出的震级为ＭＳＺ７．９。文中列出并分析了有关这次地震的全球范围大量地震台站记录的面波的周期和振幅资料，认为这种较大的差异主要来自我国测定平均震级时大量使用近台和面波周期远小于２０ｓ的资料。１９９０～１９９７年世界上发生了９次ＭＳＺ７．８的大地震，除一次外我国给出的ＭＳ皆低于７．８。而另４次我国测定的ＭＳ≥８．０的巨震，ＰＤＥ给出的ＭＳＺ则远低于７．８，这说明我国目前通用的测定面波公式和方法有缺欠，尤其不适合测定大地震的震级。

On November 8,1997,a strong earthquake attacked Mani area in the north of Tibet The magnitude of the quake determined by the Chinese network is M S 7 4,while the magnitude given by PDE is M SZ 7 9 In this paper,the periods and amplitudes of the earthquake surface waves recorded by a large number of seismographic stations in the world are presented and analysed,considering that such difference mainly results from using a large number of data recorded by near stations and using surface waves of much less than 20 s for determining the mean magnitude of the quake in China From 1990 to 1997,altogether 9 large earthquakes of M SZ ≥7 8 occurred in the world,but the magnitudes of all these quakes (except one)determined in China are lower than M S 7 8 While as for another 4 great earthquakes of M S≥8 0 determined by China,the magnitudes( M SZ )of these quakes given by PDE are far lower than 7 8, indicating that the formulas and methods for determining surface waves currently used in China have some shortcomings and are not suited for determining the magnitudes of great earthquakes in particular