DEVELOPMENT OF A MATHEMATICAL MODEL FOR THE PULSE-FREE PART OF THE NEAR FAULT EARTHQUAKES FOR THEIR TIME DOMAIN SIMULATION

The complicated nature of near-field earthquakes and its effects on the structures, especially MDOF systems, have questioned the credibility of design spectra usage for these kinds of seismological events. In comparison to the far field ground motions, a velocity pulse can be detected at the beginning of nearfield earthquakes. This pulse is main factor for many disastrous effects on flexible structures as they can impart a considerable amount of energy to the low frequency structural systems. Therefore, it is desired to provide a mathematical representation of the near-field records for problems which lack recorded motionwith those specific characteristics. Many researchers have tried to propose a mathematical model for the velocity pulse present in near field earthquakes. However, neglecting the residual (pulse-free) part of those records could lead to certain inadequacies of the resulting simulated near field records. In this study, using Papageorgiou’s pulse model, a simplified model for the Fourier transform of the residual part of near-fault records is proposed for their simulation. The model can be calibrated using a number of parameters to properly match the target records. Subsequently, regression analyses are performed in order to relate the model’s parameters to the seismological characteristics of the event. Finally, an algorithm ispresented to combine the velocity pulse obtained from Papageorgiou’s model and the residual record generated using the proposed mathematical model. Various parameters such as, moment magnitude, epicentral distance, etc., are involved in producing the residual record. MATLAB program is used for numerical analyses.

کلیدواژه ها:

Velocity Pulse ، Pulse Shape ، Background Earthquake ، Near-Fault Earthquakes