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发展了一种用小震记录求和和滤波预报特定地点未来大地震地面运动的简便方法,并用洛马普列塔地震(M=7.0)同一地点的余震(M=3.7～4.0)记录模拟主震强运动试验了这一方法。选用凹凸体破裂模型,其中断层面上平均的均方根应力降不随地震矩改变而改变。观测谱表明从3级余震直到7级主震的应力降均不变,而地震矩相差约6个量级。每次模拟对一个个余震图引入与传播破裂相对应的时间延迟后求和,并体现方向性和场地响应。模拟方法遵循常数应力降和振幅谱ω~(-2)滚降模型。当与主震滑动速度函数褶积时,余震拐角频率以上的余震和高频能量不减少,这和早期的求和方法有所不司。尽管每次模拟只用一个余震波形,但大多数情况是模拟的主震记录谱(0.6～20Hz)、峰值加速度以及持续时间与观测的强运动记录比较符合。这种一致性表明:主层的场地响应在加速度约0.3g以内保持基本线性特征。求和余震记录表明具有和主震记录一样的依赖于场地的f_(max)值。因此,f_(max)是场地效应,不是主破裂过程的特征。
A simple method of summation and filtering of small earthquakes records and predicting the ground motion of future earthquakes in a particular location has been developed. The aftershocks (M = 3.7 ~ 4.0) recorded at the same site in the Loma Prieta earthquake (M = 7.0) Strong exercise test this method. Asperity rupture model is selected, where the average root mean square stress drop over the fault plane does not change with the change of seismic moment. The observation spectra show that the stress drop from Level 3 aftershocks up to Level 7 mainshock remains unchanged, while the seismic moments differ by about 6 orders of magnitude. Each simulation sums up one aftershock map with the time delay corresponding to propagation and rupture, and reflects the directionality and site response. The simulation method obeys the constant-drop-stress and amplitude-spectrum ω ~ (-2) roll-off model. When convolution with the mainshock sliding velocity function, the aftershocks and high-frequency energies above the aftershock corner frequency do not decrease, which is not the same as the earlier summation method. Although only one aftershock waveform is used for each simulation, in most cases the simulated mainshock recording spectrum (0.6-20 Hz), peak acceleration and duration are in good agreement with the observed strong motion recording. This consistency indicates that the main site’s response to the site maintains a basic linearity within about 0.3 g of acceleration. The summation aftershock record shows the same field-dependent f_ (max) value as the main shock record. Therefore f_ (max) is a site effect and not a feature of the main rupture process.