关键词: Napa地震, 震动图, 衰减关系, 偏差校正

Abstract: A brief description of the reliability of shakemaps is that shaking is relatively reliable near seismic recording stations, and is poorly constrained far away from stations where ground motion predictions must be relied on. We try to improve the reliability of the shakemap of the Napa earthquake constrained by the seismic source, the decay law of ground motion parameters(GMP)and the inter-earthquake bias correction term. Based on the point-ellipse and fault projection plane source model, using the method of rapid generating shakemaps considering site effects, the shakemap of peak ground acceleration(PGA)for the Napa earthquake M_W6.0, August 24, 2014 was prepared. In this process, 4 sets of ground motion prediction equations were used, including the long-and short-axis attenuation relationships in western China, the attenuation relationship of fault projection distances in the Sichuan-Tibet area and the attenuation relationship of Boore in the NGA-West2 project. Furthermore, the distribution of the shakemap was constrained by the seismic station observations, and the bias correction of the estimates were also be made by the deviation term between seismic observations and estimates. The differences of the shakemaps of different source characteristics, different attenuation relationship models, and whether or not a bias correction was considered were compared. It was concluded that the reliability of ground motion estimation is associated with unconstrained source dimensions for large earthquakes where the distance term in the GMPE is most uncertain. The addition of ground motion observations can reduce uncertainties over data-constrained portions of the map. The differences between the estimated values of different GMPE and the actual observed values can be reduced with the bias correction term applied in the shakemap, and the regional propagation characteristics of seismic waves for specific events are more reasonably described than before.

Key words: Napa earthquake, shakemap, ground-motion prediction equation, Bias correction