中文摘要：

将全球分为15个研究区，用19002009年Mw≥7．0地震目录，统计分析了各区大地震与月球交点运动周期的关系，得出15个研究区中有l0个区，大地震存在统计意义上的18．6a周期：活跃段为12．4a，平静段为6．2a；环太平洋地震带北、南、西、东4大区的大地震，不仅有这样的周期，而且其地震活跃段的时间存在一定规律．用第6个18．6a（1991～2009年）期间的大地震，检验据前5个18．6a（19001990年）地震目录所得18．6a周期的稳定性和实用性，发现有这种周期的地区多数的周期性是稳定的．大地震18．6a周期的可能成因有：（1）18．6a潮波通过调制日潮和半日潮调制大地震；（2）上地幔内流体的潮汐（地内潮）作用；（3）18．6a潮波通过影响地球自转变化调制大地震．

英文摘要：

Dividing the world into 15 study areas and using the earthquake catalogue of Mw≥7.0 during 1900-2009, we make a statistical analysis of the relationship between seismicity of each area and the period of lunar nodal motion. The result shows that among the 15 areas, 10 areas exhibit an 18.6-year cycle of great earthquakes in statistical sense, which consists of a 12.4 year active section and a 6.2-year quiet section. In the eastern, northern, southern and western areas of the Circum Pacific seismic belt, such a periodicity is present and their active sections have certain regularity. In terms of seismic events during the sixth cycle （1991~2009）, this study has tested the stability and applicability of the 18.6 year periodicity derived from earlier five cycles （1900~ 1990）. It is found that most of periodicities are stable in the regions with such characters. The possible mechanisms of the 18.6-year periodicity are as follows. （1） Earthquakes are modulated by the 18.6-year tide via day and half-day tides. （2） Effect of fluid tide in upper mantle （tide within the Earth）. And （3） earthquakes are dictated by 18. 6-year tide through variation of Earth rotation.