蒙古国地区背景地震危险性分析

A Study on Hazards of Background Seismicity in Mongolia

根据蒙古国及其周边地区的背景地震目录（M≤6．0），采用空间光滑地震活动性的方法研究了蒙古国地区背景地震危险性水平，给出了蒙古国50年超越概率10％的峰值加速度分布图。结果表明蒙古国大部分地区背景地震危险性水平为0．05g，部分地区高达0．1～0．15g，意味着蒙古国地区背景地震危险性高，在进行地震危险性分析和地震区划时应充分考虑背景地震活动，采用不同起始震级的地震活动性模型计算得到的地震危险性水平具有较大的空间差异，因此在采用空间光滑地震活动性模型进行地震危险性分析时应采用多个模型加权平均的方法，平衡地震频度和地震震级的影响。

In this article,we calculate seismic hazards from background seismicity by using a spa- tially smoothed seismicity model for Mongolia,and we obtain a peak ground acceleration （PGA） map for 10% probability of exceedance in 50 y. We propose two seismicity models to calculate seismic hazard maps for 10% probability of exceedance in 50 y. The results show that the seismic activity model and the seismic hazard results, both calculated by using the instrumental seismic catalog （M≥3.0）, can reflect contemporary seismic activity levels and seismic hazard levels of the Mongolia area. In addition, the seismic activity model and the seismic hazard results, both of which are calculated by using historical earthquake data （M≥5.0）, can quite well represent the seismic hazard level of moderate earthquakes in Mongolia. The two seismic hazard maps both show that the background seismic hazard level is 0.05 g in most areas of Mongolia and that the values of this parameter are high,at 0.1～0.15 g,in other areas,which indicates a background of high seismic hazards in Mongolia. Therefore, it is highly necessary to completely consider the im- pacts of background seismicity when implementing seismic hazard analysis and seismic hazard mapping for Mongolia. Moreover,we compare two seismicity models. The results also illustrate significant spatial differences between the seismicity models with different minimum complete magnitudes. Therefore, when adopting a spatially smoothed seismicity model to analyze seismic hazards for Mongolia, the weighted average of several different models should be considered to balance the impacts of earthquake occurrences and magnitudes.