Study On Uncertainties In The Parameters Of Psha

This study is in the uncertainties and theirs influence of some critical seismicity parameters of PSHA method. Three principal topics were discussed here, the uncertainty in seismic province division for seismicity statistical analysis and its influence on seismic hazard, the uncertainty in evaluating b value and earthquake average annual occurrence rate (v4) and its influence on seismic hazard, the role of spatial distribution function in uncertainty analysis of seismicity parameters.An important idea mentioned here for the first time is that the seismic province is a special term for a purpose of probabilistic seismic hazard analysis with considering the spatial and temporal dependence of earthquakes. It is a advancement of PSHA methodology in aspect of taking into account of spatial inhomogeneous of seismicity. The concept of seismic province comes from the concept of seismic active belt, but they are very different. It is emphasized in this paper that the seismic active belt is important base for research on the process of earthquake occurrence, but the seismic province is just a statistic scope for seismicity parameters evaluating.In this paper, the source of uncertainty in seismic province is discussed. The uncertainties are caused mainly by the division of the area with low level earthquake activity, taking into account the deep earthquakes belt in North-Hast of China or not in PSHA, division of the North-South seismic belt, variety of the scale of seismic active belt, etc. They all make some great influence on the uncertainty of seismic province boundary in China. The uncertainties of seismic province division directly cause the uncertainties of earthquakes sample space division, so the prediction of earthquake activity level for the same region willvary with it, and the assessment of seismic hazard will vary with it too. in Northern China, the COV of intensity is 0.04 for average level and 0.11 for maximum, the COV of PGA is 0.3 for average and lager than 0.85 for maximum.There are many contributing factors for b value and v4 calculating, and change with different seismic province. In this study, the uncertainties of several main factors and its influence are discussed. The results show that in Northern China, the maximum change of b value in Tanlu and Fenwei seismic province is separately 0.2 and 0.18, v4 is separately 1.4 and 1.61, and the maximum change of b value in Hebci seismic province is only 0.045, v4 is 0.3.Uncertainties of b value and v4 can cause considerable uncertainties of seismic hazards of the site. It was studied here in two ways. First, the influence of this kind of uncertainty for just one seismic province is evaluating, and then the influence for several provinces are evaluated. The results show that in those seismic provinces with considerable uncertainty in seismicity parameters the uncertainty of seismic hazard in site is similar both in this two cases, but in those seismic provinces with small uncertainty in seismicity parameters the uncertainty of seismic hazard in site vary significantly. The conclusion is drawn that when the influence of uncertainty in seismicity parameters is evaluated, the correlative seismic provinces must be taken into account together.The feature of inhomogeneous of seismicity in one seismic province is represented by spatial distribution function. It also makes the influence on seismic hazard caused by uncertainty in seismicity parameters change in different spatial location. Result mentioned in this paper shows that uncertainties of seismic hazard for the case of homogeneous seismicity are smaller in average level than the case of inhomogeneous seismicity, but in the region with higher magnitude potential sources the result is reverse and the uncertainties are more larger.At the end of this paper, the influences caused by the uncertainty of each parameters are compared. The result shows that for the average level of seismic hazard uncertainty, the main influence comes from the uncertainty of seismic province boundary. Sites they can affectedare different. The-uncertainty of seismic province boundary can only affect those sites near the seismic province boundary, the uncertainty of seismicity parameters can mainly affect those inner sites of seismic province. The uncertainty of spatial distribution function can affect local sites in those potential sources with higher upper limit magnitude.