The spatial distribution function assigns seismicity parameters of seismic zone and belt to the potential earthquake source area seismic by the magnitude interval, determination of the spatial distribution function is one of the key technologies to comprehensive probabilistic seismic hazard analysis methods, and the results will directly influence seismic hazard analysis results of the calculated sites. However, the spatial distribution functions are hard to get by statistics due to serious lack of seismic samples, and evaluation factors used in the actual work are too complex and not independent, the spatial distribution function is lack of reliability. In this paper, Bohai seismic tectonic area is chosen as an example; geological data are obtained from the newly built offshore oil platform engineering in recent decades, while seismic activity data are obtained by checking from historical difficult seismic parameters. Five factors are adopted in this area, including potential seismic focus area, seismic tectonic, seismic activity level, long-term forecasts, and strong earthquake recurrence interval and construct empty segment. Spatial distribution function of Bohai Sea earthquake structure area is obtained by weighted comprehension; it reflects the spatial and temporal heterogeneity of seismic activities in the area, and provides the calculation parameters for the probabilistic seismic hazard analysis.

Dynamic shear modulus ratios and damping ratios of soil are the parameter of indicating dynamic nonlinearity of soil, and the necessary parameter of seismic site analysis. The 372 pairs of soil samples’ dynamic nonlinear parameters, which were tested by dynamic tri-axial tests in about 40 the seismic safety evaluation reports of ocean oil platforms in the Bohai Sea, were collected and corrected. The dynamic shear modulus ratios and the damping ratios of various soil types with different depth in the Bohai seafloor were calculated and their statistical mean values were obtained. The statistical mean values are reasonable and are the important supplements in case that the tested soil samples are not enough in the Bohai Sea sites.