Peak ground acceleration (PGA)in the near field is associated with earthquake damage, but practical instances of the impact of PGA distribution in the near field of different types of fo-cal mechanism is rarely reported.Using the intensive digital seismic records of the capital circle strong motion network,this paper studies two earthquakes that occurred in April 2003 with an epicenter located in Tangshan.Using data from the strong motion network and the temporary seismic network in Sichuan,Gansu,and Shanxi,it also studies two earthquakes that occurred in July and August 2008 with an epicenter located in Wenchan.By using a function of the thematic map in ArcGIS software,the distribution of both the horizontal synthesis and vertical PGA is es-tablished,obtaining the differences in earthquake PGA distribution in the near field from the faults and strike-slip faults,and the thrust and strike-slip faults.In this paper,we study the impact of different focal mechanisms in the Ninghe and the Wenchuan earthquake on PGA ;the difference in the influence of various focal mechanisms to PGA is especially striking.The results show that this difference is prominent,and that the distribution of major earthquakes PGA is complex in the near field,while that of medium-small earthquakes is also complex.The most crucial place for death and destruction is in the near field.Spectrum analysis established that there are differences in the lower frequencies of seismic waves.Now that there are more buildings and that a greater proportion are multistory and large,the self-vibration period is longer.High values in PGA of nearly vertical strike-slip earthquakes are symmetrically distributed along the fault,while normal faults and reverse faults are concentrated in the hanging wall.The distribution of PGA is complex in the near field,and it is worth noting that the phenomenon of low frequency dip-lip earthquakes is crucial to the input of power and materials in emergency rescue following destructive earth-quakes.%利用首都圈强震台网比较密集的数字地震记录，研究2003年4月发生在唐山震区的2次4级地震。利用布设在四川、甘肃、陕西的强震台网和临时强震台网的资料，研究2008年7月和8月发生在四川汶川的2次6级地震。得到正断层和走向滑动断层、逆冲断层和走向滑动断层的地震近场 PGA 分布的差异。结果表明，这种差异是显著的。不仅大震的 PGA 近场分布复杂，中小地震也是如此。经频谱分析发现，这种影响出现差异的地震波频率较低，城市化的建筑向高层大型发展，其自振周期相应较长。近直立走向滑动地震的 PGA 高值区沿断层对称分布，而正断层和逆断层则集中在断层上盘，这对于破坏性地震应急救援中力量、物资的投入有借鉴意义。
展开▼
