凹凸体位错非均匀性对断层引起地表位移的影响

Influence of non-uniform asperity dislocation on the surface displacement induced by faults

在已有的凹凸体震源模型基础上考虑凹凸体位错非均匀性,提出改进的凹凸体位错模式。新的位错模式随机设置凹凸体上各子断层位错量,同时在凹凸体与背景区交界处设置位错平缓变化的区域。以1989年美国Loma Prieta地震为例,计算不同断层位错模式下引起的地表位移,并与反演得到真实情况下地表的位移作对比,验证改进凹凸体位错模式的可靠性。结果显示,使用改进的渐变凹凸体非均匀位错模式计算时,与真实情况下竖向地表位移差大于8 cm的区域面积为43 km^(2),相较凹凸体均匀位错模式缩减25%;水平地表位移差大于8 cm区域面积为117 km^(2),相较凹凸体均匀位错模式缩减达31%。利用改进的渐变凹凸体非均匀位错模式,计算1679年三河—平谷大地震在北京地区形成的地表位移场。北京市外,最大竖向地表位移大于4.8 m,最大水平地表位移大于2.6 m,均出现在三河附近;北京市内,通州区至平谷区一带地表位移最大,最大水平地表位移大于2.6 m,最大竖向地表位移大于1 m。研究结果可为今后北京地区的抗震设防提供参考。

A large number of surface structures along active faults are damaged during earthquakes.Accurate estimation of the surface displacement induced by fault dislocation is critical as it accounts for the damage to surface structures.A valid asperity dislocation model helps calculate surface displacement more accurately.To examine how asperity heterogeneity affects surface displacement,this paper proposed an improved asperity dislocation model that considers the non-uniformity of asperity dislocation based on traditional asperity dislocation models.To validate the proposed asperity dislocation model,we chose the 1989 Loma Prieta earthquake as a target event.Surface displacements that induced the Loma Prieta earthquake under different asperity models were calculated.Results were compared with actual surface displacement measurements obtained by inversion.An area of 43 km^(2) calculated by the proposed non-uniform asperity model demonstrates a difference in surface displacement exceeding 8 cm compared with actual results,which is reduced by 25%compared with the results derived from the uniform asperity dislocation model.The area with a difference in the horizontal surface displacement exceeding 8 cm is 117 km^(2),which is reduced by 31%compared with the results derived from the uniform asperity dislocation model.Furthermore,this paper applied the proposed non-uniform asperity dislocation model to calculate the surface displacement induced by the 1679 Sanhe—Pinggu M8.0 earthquake.Areas with surface displacements greater than 1 m and 2 m were summarized,and the maximum horizontal and vertical surface displacements were calculated.Outside Beijing,the maximum vertical and horizontal surface displacements occur near Sanhe City and exceed 4.8 m and 2.6 m,respectively.In Beijing,the maximum vertical and horizontal surface displacements appear in Tongzhou and the Pinggu District,which exceed 1 m and 2.6 m,respectively.The research results provide a reference for future seismic fortification in Beijing.