汶川地震的6区域模型加速度峰值衰减关系

利用加速度记录直接拟合衰减关系时,几乎所有现行文献都采用圆模型,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,为修正这种偏差,作者曾提出了4区域的椭圆模型,但是该模型忽略了断层长度垂直范围的2个区域,导致其等震线形状没有沿着断裂方向"发散开"的趋势。且不能反映破裂方向对短轴衰减的影响。该文提出的加速度衰减关系的6区域模型,通过过断层方向和过断层两端点且垂直于断层6条分割线,将地震记录观测点位置分为6个区域,通过研究沿分割线方向的衰减关系得到地震动衰减与衰减路径所处区域的相关性。以汶川8.0级地震为例,说明模型下的6条衰减关系,各自代表的物理意义以及汶川地震地震动峰值加速度衰减的区域特性。在拟合精度上,该模型较圆模型有大幅提高,比4区域椭圆模型略高,在反映地震动区域特性上,比4区域模型更加细致的反映了断层破裂方向效应和上下盘效应。

Fitting of Acceleration Peak Attenuation With Six area Model for Wenchuan 8.0 Magnitude Earthquake

At present, euqi distance circle model is generally used for directly fitting acceleration peak attenuation. Epicenter distance or focal distance is the only coordinate statistical parameter of seismic station. For large earthquake with a long fault, the iso seismical curve of euqi distance exists serious deviation from realistic iso seismal curve. Six area model was addressed to correct the deviation. With the model, seismic station was divided into six areas by two cut lines of coincided with fault and four cut lines perpendicular to fault. The acceleration peak attenuation curve along cut lines was fitted to analyse the relationship between attenuation curve and area seismic station. Take Wenchuan earthquake for an instance, the accuracy of the model is much higher than that of euqi distance circle model and a little higher than that of four area elliptical model. And the model is more accurate than four area elliptical model in reflecting hanging and foot wall effect and direction effect.