Relationship Between Lunisolar Effect and Strong Seismic Activity in Yunnan

Yunnan province is located at the southwest part of China, and near the boundary of the Eurasian plate and the Indian plate.The extrusion of the Indian plate northeastward to the Eurasian plate causes complex geological features and high seismicity in the highland of Yunnan. The variety of seismic activity in Yunnan serves as a natural laboratory for seismological studies. The complexity in tectonics results in spatial non-uniformity of the earthquake distribution. Astronomical background of the rise and fall of strong seismic activities in the 20th century in Yunnan is analyzed in detail in this paper.The lunar nodal tides, generated by the variation of the inclination between the Moon'spath around the Earth and the equator with a period of 18.61 years may be a reason of the seismic activity with long periods.The analyzing result shows that three of the four strong seismic periods with earthquake magnitude larger than or equal to 6.7 in the 20th century started at the year or next year, when a maximum value of the inclination between the Moon's path around the Earth and the equator happened.Only the first seismic active period did not.Therefore, the total consistent probability is about 80%.Moreover, both the solar and seismic activities have a quasi-period of 11 years.On the basis of above we make an extension of the 4 groups with the period of 11 years by the earthquake with the most magnitude over years of the 20th century, and estimate the magnitude of the first earthquake in the future seismic active period in Yunnan.Considering the two astronomic factors, and according to the situation of the inclination between the Moon's path around the Earth and the equator, in addition to the solar activity at the present, we think that next seismic active period in Yunnan will probably start at AD 2006 or 2007, and it may last to 2015.During this period there will be more earthquakes with magnitude larger than or equal to 6.7.It means a new period with serious natural hazards in Yunnan.The location for the future first strong earthquake is also suggested in this paper.