基于四区域椭圆模型的汶川8.0地震加速度峰值衰减关系拟合

Wenchuan 8.0 rank earthquake acceleration peak attenuation curve based on a four-area elliptical model

利用加速度记录直接拟合衰减关系时,现行几乎所有文献都采用圆模型,以震中距或震源距为观测点坐标位置的唯一统计量。对于长断层的大震而言,等震线的圆模型假设和实际等震线图存在严重的偏差,加速度峰值在沿断层方向的长轴和垂直于断层方向的短轴衰减关系差异非常明显。提出的加速度衰减关系的四区域椭圆模型,按断层破裂方向的长轴和过断层为中心垂直于长轴的短轴将地震记录观测点位置分为四个区域,以烈度等值线为参考,给出了四个区域内各自的加速度峰值等值线的椭圆近似曲线。并在此基础上得出了汶川8.0级地震加速度峰值在两个长半轴和两个短半轴方向上的衰减关系,和圆模型相比,该模型在精度上更加可靠,且能够反映断层破裂方向效应和上下盘效应,具有较强的工程应用价值。

At present,an equal-distance circle model is generally used for directly fitting acceleration peak attenuation curve,epicentral distance or focal distance is only the coordinate statistical parameter for a seismic observation station.For large earthquake with a long fault,the isoseismic curves of the equal-distance circle model exist serious deviation from realistic isoseismic curves.There is enormous differences between the acceleration peak attenuation curve along the long axis and that along the short axis.An four-area elliptical model was proposed here dividing seismic observation stations into four areas according to the long axis and the short axis.Every elliptical acceleration isoseismic curve in four areas was respectively figured out using interpolation in relation to seismic intensity isoseismic curves.On this basis,Wenchuan earthquake acceleration peak attenuation curve was derived along two long semiaxes and two short semiaxes.Comparing Wenchuan 8.0 rank earthquake acceleration peak attenuation curve using the four-area elliptical model with that using the circle model,the former was more close to the real situation and it could reflect the hanging and foot wall effect of fault and the direction effect of earthquake.