我国境内瑞利波的相速度

本文利用新不列颠岛两个地震在十二个基本台站所记录到的瑞利波,计算了我国不同地区的相速度.着重讨论鉴别和对比不同台站记录中同一震相的方法.在大部分台站的记录中,见到有周期约为35秒的相位,和后面的位相比较,它的周期较大,振幅较小.波形的对比对初步鉴别震相有很大的帮助.详细的震相对比是根据周期随距离变化的规律和各震相到时的规律.两个地震所得的相速度很符合.计算的结果表明:利用三台计算相速度时,如果射线的路程差别较大,海洋路程的校正是不能忽略的.因为有关我国地壳构造的资料还很少,我们所得的瑞利波相速度只能与普瑞司修正后非洲大陆的相速度理论相比较,由此得到我国不同地区的地壳厚度.这样所得的厚度,虽然不能视为最后的结果,但是它们仍然表现与主要地质单元之间有密切的联系.

PHASE VELOCITIES OF RAYLEIGH WAVES IN CHINA

The phase velocities of Rayleigh waves in China were obtained by using the seis- mograms from twelve stations in China.Two earthquakes from New Britain Islands were chosen.The amplitudes of Rayleigh Waves with the period of about 35 seconds are considerably smaller than their following phases with shorter periods.This particular feature of the seismograms can be traced from most of the stations.It makes the cor- relation more feasible.Detailed correlations are obtained by analyzing the variation of periods with distances and also the arrival times of each crest of Rayleigh waves in the seismograms.The phase velocities of separate regions as computed from two different earthquakes are in good agreement.The results show that in calculating the phase velo- cities with tripartite method,the corrections due to different oceanic paths can not be neglected if the angular distances between them were great.Because the parameters of the earth crust in China are not well-known,we have to compare these calculated phase velocities of Rayleigh waves in China with the revised phase velocity nomograms of Rayleigh waves by Press,based on the materials obtained in Africa.The crust thick- nesses in separate regions are thus computed,the results being merely tentative.How- ever,unless more geophysical data were available,these data as given by this method still show a rather close correlation with the principal tectonic features in China.In the region of Tibetan Plateau,the phase velocities are very low,and the calculated thick- ness of the earth crust there is 74 kms;whereas in the region of southeastern coast,the phase velocities are high,and the calculated thickness is only 20 kms.