A Preliminary Study On Earth Rotation Effect Of Medium-small Earthquakes Around The Epicenter Before The Strong Earthquakes

Many scientists always pay close attention to the relationship between earth rotation and earthquakes. The relationship between earth rotation and earthquakes in different areas are unequal, and the relationship between different periodic components of LOD and earthquakes are different. We found there was a good relationship between the seasonal variation of LOD and the medium-small earthquakes occurred near the area of epicenter within several years before the main shock when we researched the relationship between earth rotation and the2008M8.0Sichuan Wenchuan earthquake on May12,2008. To certify whether it was a coincidence or not, we researched the relationship of the seasonal variation of LOD with the medium-small earthquakes occurred near the area of epicenter within several years before the16M≥7.0earthquakes in Chinese mainland after1970and two foreign earthquakes.The earthquakes occurred in the regions of aftershocks which occurred within one year after the main shock had been chosen to compute the minimum complete magnitude. We chose the medium-small earthquakes whose magnitudes were bigger than the minimum complete magnitude to analyze the relationship between earthquakes and LOD. The four methods had been used:(1) Compared the seasonal variation of LOD with magnitude-time curve to find the medium-small earthquakes in the regions of aftershocks within several years before the main shocks occurred in the acceleration periods of seasonal variation of earth rotation or in the deceleration periods.(2) Computed the ratios of earthquakes occurred in acceleration periods of the seasonal changes in the Earth’s rotation in the region of aftershocks to earthquakes occurred in deceleration periods within a few years before the main shocks, and found whether the ratios changed significantly or not before the main shocks.(3) From the distribution of epicenter of the medium-small earthquakes in the regions of aftershocks within several years before the main shocks occurred in deceleration and acceleration periods of the seasonal variation in earth rotation, we wanted to see whether these earthquakes often occurred in the same periods of the seasonal variation in earth rotation or not.(4) Compared the curve of number of earthquakes with the curve of LOD to find whether there is a good relationship between them.The following conclusions had been found from this research:(1) In some areas, the medium-small earthquakes in the regions of aftershocks within several years before the main shocks often occurred in the acceleration periods of the seasonal variation in earth rotation. On the other hand, the earthquakes often occurred in the deceleration periods in other areas.(2) The results that the medium-small earthquakes in the regions of aftershocks within several years before the main shocks often occurred in the acceleration periods of the seasonal variation in earth rotation or in the deceleration periods were different in different regions.(3) If the medium-small earthquakes in the region of aftershocks within several years before the main shocks often occurred in the acceleration periods of the seasonal variation in earth rotation, the main shocks didn’t necessarily occurred in the acceleration periods of the seasonal variation in earth rotation, and the main shocks didn’t necessarily occurred in the acceleration periods of the decadal fluctuation in earth rotation. There was no obvious correlation between them.From the conclusion we can see that it is different from the seasonal variation of LOD and other periodic components of LOD, and there is a good relationship between the seasonal variation of LOD and the medium-small earthquakes occurred in the region of aftershocks within several years before the main shocks. The main characteristics and innovation of this research is that we pay attention to the area of hypocenter body and research the special relationship between the seasonal variation of LOD and the medium-small earthquakes in the regions of aftershocks when the source body is critical unstable state. This correlation is more obvious than other periodic component of LOD. And there is clear physical meaning between them. This has guiding significance for us to forecast the strong earthquakes in future.