Strong Ground Motion Attenuation Relationship Of Small-Moderate Earthquakes

In the paper the development is reviewed systemically for the study on the attenuation laws of the earthquake ground motion and also are the data used in these studies and the results. Because the data used in these studies are mainly from the large earthquakes, magnitude greater than 5.5, these results are not very suitable for the estimation for the small-moderate earthquakes. Now the diffuse earthquake has been used in the earthquake hazard analysis for the nuclear power plant. So we collect some records from the small-moderate earthquakes with magnitude between 4.0-6.5 and distance from the source less than 70 km. Then we develop the attenuation laws of these earthquakes expecting to reflect the attenuation laws of the diffuse earthquakes.The records we used are mainly from three parts: strong ground motion data before 1992's; data from SCEC(South California Earthquake Catalog); NSMP( National Strong Motion Project). After we developed the attenuation laws, we analysis the attenuation characteristics for the PGA and SA with different damping ratio. Here we mainly concentrate on the effect of the distance and the magnitude. Then we compare our result with others' and analysis the reasons for the difference between these results.The envelop functions of ground motion for the small-moderate earthquakes in the near-source field are different with those of the larger earthquakes. There are not stationary part any more in the envelop function of these ground motions. After we analyze the characteristics of these envelope functions we take a exponent function instead the three part function. Using this function we research the attenuation law of the duration time of the records we used in PGA. The results show that the effects of the distance take a more important role. We give a primary discussion of the reason by analyzing the M-R figure of the duration time.