华北、西南一些地区地震发生在地壳浅部的证据

依据区域小孔径数字地震台网对河北省唐山、张北、怀来，山西省大同和云南省剑川、禄劝、姚安等７次地震的定位或重定位结果，并结合相应区域个别大震用远场资料反演的震源深度结果，以及山西省临汾遥测地震台网重新测定的震源深度结果，与以往地震目录中给出的震源深度测定结果进行对比分析，发现小孔径台网的震源深度测定结果基本分布在地表至地下十几千米的范围内．而以往给出的测定结果中，震源深度大致分布在地表至地下30ｋｍ 的深度上，与其平均值相差一半至一倍，两者之间的差别非常显著．分析认为，小孔径数字地震台网的测定结果可能更接近震源深度分布的真实情况，即上述地区的地震应是发生在地壳浅层内．对造成上述情况的原因，进行了初步的讨论，并提出改善震源深度测定精度的建议和措施．

SOME EVIDENCES FOR EARTHQUAKE OCCURRENCE IN THE SHALLOW CRUST IN SOME AREAS OF NORTH CHINA AND SOUTHWEST CHINA

The parameters of hypocentral location are important fundamental data for the study of seismology and the earth interior physics; among them, the focal depth is a very important one but can hardly be measured with higher precision. With the increase of seismic stations in number, the heightening of observation quality and the improvement of determination method, such a situation has been changed much. In this paper, the results of hypocentral location and re location by 7 small aperture digital seismic station networks at Tangshan, Zhangbei and Huailai of Hebei Province, Datong of Shanxi Province and Jianchuan, Luquan and Yaoan of Yunnan Province are used. Using these results together with those of focal depth inversion by far field data of some individual large shocks in corresponding areas and those re determined by the Linfen telemetric seismic network of Shanxi Province, a comparison with the results of focal depth determination in the past earthquake catalogues is made. It is found out that the focal depths determined by the small aperture seismic networks are basically distributed in the range from the earth surface to ten odd kilometers underground. In contrast, the focal depths determined in the past are mostly distributed at the depth range from the earth surface to 30 kilometers underground. Besides, there is a difference of 50% to 100% between the average values of the two cases, which is quite an obvious one. From the result of analysis, it is considered that the results determined by the small aperture seismic networks may be closer to the reality of focal depths distribution. That is to say, earthquakes in the above mentioned areas should be distributed in the shallow part of the crust. The causes that lead to the above situation are discussed preliminarily, and some suggestions and measures for improving the precision of focal depth determination are put forward.