关键词: 长江下游地区, 固体潮, 位相, 统计检验, 混沌

Abstract: Phases of mainshocks (M≥5.0,1900～1990) in the lower Changjiang River region (30～34°N,116～122°E) in the Eastern China were determined by means of the formulaser for the theoretical tidal gravity.Distributions of lunar and solar hour angles,lunar and solar ecliptic longitudes,luni-solar phases,and phases of the 8.85-yr lunar perigee cycle and the 18.6-yr lunar nodal cycle of these samples were evaluated by Schuster's test and chi-square test for which the formula used in Kilston & Knopoff (1983) was modified into (6) in this paper.To avoid fortuity,especially in the case of smaller sample,and missing some possible periodicities,the samples with magnitude from 5.0 to 5.7 were tested one by one.Phases of the semidiurnal and fortnightly theoretical tidal gravity were also determined and evaluated.This investigation has uncovered that the principal earthquakes in the study region show statistically non-random lunar and solar periodicities as follows:1.semidiurnal periodicities displayed by the binodal distribution of the hour angle of the Sun (P_R=0.023,χ²=7.576) and the pattern of semidiurnal gravitational tides (P_R=0.017,χ²=8.167);2.semimonthly periodicity shown by the binodal distribution of luni-solar phases (P_R=0.011,χ²=8.985) and fortnightly tidal periodicity (P_R=0.061,χ²=5.566);3.one year periodicity of the solar ecliptic longitude of the events with M_s≥5.1(P_R=0.035,χ²=6.712) and 8.85/2 years periodicity given by twice the longitudes of Moon's perigee of the mainshocks with M_s×5.2 (P_R=0.043,χ²=6.309).Of above periodicities,the most remarkable and stable one is half the synodic month.Such periodicities uncovered in this study suggest that occurrences of earthquakes may have the characteristics of chaotic patterns.Effects of the exogenetic stresses on occurrences of earthquakes should belong to the nonlinear interactions.It is difficult to set some models to explain the complex phenomena by means of the classical physics.At present,such investigations are only trying to seek some empirical regularity of seismicity.

Key words: Lower Changjiang River region, Tidal gravity, Phase, Statistical test, Chaos