Abstract: Based on the earthquake catalogue of the seismic moment tensor supplied by Ha rv ard Univ ersity, 242 earthquakes (MW≥7.0) occurred on the whole globe during the recent 20 years (from January 1,1980 to December 31,1999) areselected. Th us the azimuth expression of the horizo ntal tide fo rce in the seismog enic reg ions is obtained in thi s paper. The axes P and T azimuth of each ea rthquake stress field may be deriv ed from the seismic moment tensor pa rameters from the ear thquake catalo gue, and the azimuth of the ho ri zontal tide fo rce relative to the sun and moon impo ses in the epicenter region, may also be ca lculated. The azimuth of the hori zo ntal tide force is compa red respectively with those of the ax es P and T and two g roups of fault trends, and it can be shownthat they are almo st parallel or perpendicular oneanother and the paral lel or perpendicular accorda nce is very well. The probabilities, for the g rea tear thquake occurrence with the parallel or perpendicular r dif ference within 10°, 20°and 30°, are respectiv ely mo re than 0.414, 0.736 and 0.945. The result shows that there may be a close relation between the sun, moon, the ho ri zontal tide fo rce in the seismog enic reg ions a nd the g reat ea rthquake o ccurrence. In thi s paper, it is further studied that the ho ri zo ntal tide fo rce mig ht play aco nt rolling role in the g reat earthquake occurrence.

Key words: Horizo ntal tide fo rce, Co nt rolling role, Focal mecha nism, Sei smic region