Abstract: In 1556, seismic shocks occurred in Huaxian, Shanxi Province, and in Yueyang, Hunan Province. Whether the seismic shocks belong to one earthquake? For this purpose, we studied the attenuation of seismic intensity, the similarity of the isoseismal forms of several strong earthquakes in and near Huaxian area, and the W-E-trending Qinling tectonic belt acting as a barrier for the seismic wave propagation. The results show that the boundary of seismic intensity IV of the great Huaxian earthquake lies in Xiangyang-Guangshan zone, near the 23℃ N. That is to say, there is an aseismic belt between Huaxian and Yueyang, and south of the aseismic belt there is another high-seismic intensity area up to VII. For that the epicenter must be near Yueyang, From where the seismic intensity attenuated outward and a closed boundary of intensity contour was formed. It indicates that the earthquake occurring in Yueyang is simultaneous but independent from the Huaxian earthquake in 1556. After then the high seismic frequency in Yueyang area lasted about 20 years. It means a period during which the regional stress was adjusted after the earthquake, whereas the anticlockwise rotational deformation in the upper part of Cisi Pagoda in Yueyang might result from the strong earthquake.

Key words: Huaxian, Yueyang, Seismic intensity attenuation, Anti-clockwise rotational deformation, Aseismic belt

摘要： 通过研究地震烈度的衰减、临近华县地区历次强震等烈度线形态的相似性以及秦岭东西构造带对地震动的阻挡,认为华县大地震南侧的四度线边界在襄阳～光山一带,即大致在北纬32°附近,其南侧出现一个无震感记录的地带,无震感地带以南才是岳阳地震的影响场区,它有自己的震中,震中烈度七度,向外烈度衰减有闭合的四度区边界,表明1556年发生的华县大地震与岳阳地震是同时发生的两个独立的地震。

关键词: 华县, 岳阳, 地震烈度衰减, 逆时针旋扭, 无震感地带