【摘要】 运用经验格林函数法模拟了2008年5月12日汶川8.0级大地震的近场强地面运动.拟合过程中,首先参考其他学者反演结果给出的滑动量分布的特征,确定强震动生成区的大致范围;然后利用Somerville等(1999)提出的地震矩与凹凸体面积间的经验关系式确定强震动生成区(SMGA)细小划分的初值,继而利用遗传优化算法确定以上两者的最优值及其他震源参数.数值模拟波形同实际地震观测记录在时间域和频率域分别进行了比较,结果显示,在所选取的18个观测台中,多数台站的数值模拟结果同实际观测结果符合得很好,特别是大于1 Hz的高频部分.我们发现断层面上有5个强震动生成区,其中两个的位置与其他学者反演的滑动量集中分布区相一致,但强震动生成区规模和上升时间比Somerville等(1999)获得的定标率外延的估计值要小.更多还原

【Abstract】 To further study the source process and strong motion generation mechanism of 2008MS8.0 Wenchuan earthquake,we simulated the near-field strong ground motion caused by this large event. We constructed basic source models and synthesize their waveforms using the empirical Green′s function(EFG)method for the records from 18 stations near the source region.In the EFG method,records of small events are considered as an empirical Green′s functions(Hartzell,1978).The target fault is divided into several subfaults,the areas of which are taken to be equal to the fault areas of the small events.The ground motion spawned by the large event is expressed as a superposition of the records of these small events.From physical basis of this method,we selected observed records as the EGFs from the events for which the source mechanism associated with the source effect and the hypocentral distance related to the propagation-path effects are similar to those of the target event.Then,we used the observed records from a strike-slip thrust aftershock(Mw5.6)which occurred in the southwest segment of the main fault and a strike slipping aftershock(Mw6.1)which took place in the northeast segment of the main fault.At first,we constructed a simple source model which has only two strong motion generation areas(SMGA)in the entire rupture area and estimated the location of SMGAs based on the teleseismic data inversion results of previous work.Then,we preliminarily determined the total areas of SMGAs and the quantity of subfaults N×N referring to the scaling law introduced by Somerville et al.(1999).Finally,we implemented the genetic algorithm searching for the optimized source parameters.Comparison of simulated and observed ground motions indicates the validity of the source model constructed mainly by two large SMGAs.Meanwhile a few strong motion records have 4~5isolated pulses considered to be generated from the SMGAs,therefore we construct a 5-SMGAs source model including two large SMGAs as in the simple model and three more scattered small SMGAs in the entire rupture area.After obtaining the best-fit parameters for a 5-SMGAs model,our results show that the comparison between the synthetic and the observed waveforms agree each other very well.We confirmed that there are five obvious SMGAs on the fault.Locations of the two large SMGAs are similar to the asperities from the teleseismic data inversion while the others are located far away from asperities.Finally,we examined whether the determined fault parameters follow the scaling relationships used in the recipe and found that the combined strong motion generation areas and the rise time we obtained are smaller than those values predicted by the extension value of the scaling law by Somerville et al.(1999).The strong ground motions of the 2008 Wenchuan event were well simulated in both the time and frequency domains for 18 stations by the EGF method with records of two different source mechanism aftershocks.The best-fit model shows the locations of the two large SMGAs similar to the asperities from the teleseismic inversion.The source modeled based on the proposed scaling law is larger than that of the Wenchuan earthquake.更多还原