Abstract: Based on a dataset of 550 000 earthquake events gathered from IRIS website, this article studies the periodic changes in the sun-moon-earth, sun-earth, and moon-earth spatial relationship, performs statistical analysis on its impact on global earthquake frequency, and analyzes the relationship between the statistical results and tidal forces. The results demonstrate that:1) Considering the sun-moon-earth space relationship, when the difference between the geocentric ecliptic longitudes of the moon and sun is 90° or 180°, the global earthquake frequency will be greatly elevated at a specific earthquake magnitude and focal depth. 2) Considering the space relationship between the sun and the earth, the frequency of global earthquakes has increased significantly when the earth is passing the Insects Awaken and Grain Rain points in its orbit. When the earth is passing the Vernal Equinox and Qingming points in its orbit, the global earthquake frequency increases significantly on the seventh day of the month in the lunar calendar. This number is 47.6% higher than the natural probability. 3) Considering the space relationship between the moon and the earth, an earthquake tends to be triggered at a location where the longitude is 180° ahead of the sub-lunar point. 4) The analytical results illustrate that some earthquakes are modulated by tidal force. In a specific time period, the interval of maximum tidal force corresponds to the time interval during which the global earthquake frequency increases.

Key words: celestial position, tidal force, statistics, earthquake frequency