Study on Astro-tidal-triggering Characteristics of Earthquakes in China and Its Neighbor Area—Mechanical Modal of Additional Tidal Stress Effect on Seismic Faults and Its Application

Based on the theories of the tidal stress, structural stress, seismic faults, rock fracture and slip, the mechanical modal of tidal stress effects on seismic faults is set up. Combining the tidal stress with the seismic stress, the modal describes the ways of mechanical effects on seismic faults by the tidal stress components along the sesmic compressive principal stress and the extensional principal stress. Thereby, the mechanism on tidal triggering of earthquake is touched. The tidal triggering effect on earthquakes actually belongs to the slip acceleration effect of the tidal stress on seismic faults. The patterns of the effect are classified into the compression-adding type and the compression-reducing type. On the basis of the modal, the tidal triggering characteristics of earthquakes in China and its neighbor area are studied. The study includs the following contents. Tidal stress components along the P axis and the T axis of more than one thousand earthquake focuses distributed in China and its neighbor areas are calculated. Patterns of the tidal stress effect on the earthquake faults are analyzed. Statistics of seismic fault types related with the slip-accelerating effect of the tidal stress and the relationship between the types and the patterns are made for various latitude areas. The following features are obtained: Proportion of the numbers of seismic faults related with the slip-accelerating effect of the tidal stress has decreasing trend with latitudinal rising. Among them, proportion of the strike-slip faults in the low latitude area is comparatively large but that of the dip-oblique-slip faults in the middle high latitude area is comparatively large. For the whole area, proportion of the numbers of seismic faults affected by the compression-adding type is larger than that affected by the compression-reducing type. For different latitude areas, various patterns of tidal stress effects and relevant types of seismic faults have various distribution features. At last, the earthquakes in China and its neighbor area suffered by tidal triggering effects are divided according to the structural stress areas. The lunisolar location parameters on the time of the earthquakes are calculated and the distribution patterns of the lunisolar location parameters are obtained.