Spatial Correlation Of Simulated Near-fault Ground Motion Field

With the development of economy, more and more extended structures appeared. Multiple-support excitation should be taken into account in the seismic analysis of this kind of structures. All the methods of Multiple-support excitation synthesis proposed so far need a coherence function based on records from dense seismic arrays, which made them unavailable for areas where earthquake records are insufficient. In addition, ground motion in the near-field is more complex than that in the far-field due to the effect of the source. The important engineering features of near-field ground motion, such as the directivity effect, should be considered in the multiple-support excitation synthesis in the near-fault field.A new method was developed by the team lead by the author's supervisor. In this method, the source is characterized by finite fault model, ground motions of short and long period range are simulated by the stochastic synthesis method and the numerical Green's function method respectively, then two parts of ground motions are superposed in time domain after filtering.The key procedure to apply the new method was introduced. Then, Near-source strong ground motion field in Lanzhou city and its vicinity caused by M7.0 earthquake from the middle-eastern segment of the northern margin of Maxianshan fault was simulated by the new method and used to analyze the spatial correlation. Coherence coefficients of high- and low-frequency and superposed ground motion for the specified station pairs were computed in turn to analyze the dependence of coherence coefficient on distance and on frequency. Results show that: 1. The coherence coefficient of the analyzed ground motion field is beyond 0.9 in the frequency range of lower than 1 Hz, which indicates a very good correlation, whereas that in the frequency range of higher than 1 Hz is lower than 0.7 which could be interpreted by the randomness of high-frequency ground motion;2. The coherence coefficients of high- and low-frequency and superposed ground motion all decrease as distance increases. These conclusions are consistent with those drawn from the statistical analysis of array records, which proves that simulation method by our team can characterize the spatial correlation and is available to the multiple-support excitation synthesis of extended structures.