Forecast for near-fault ground motion field:Taking Changchun City as an example

The study of near fault ground motion field distribution is one of hot points in earthquake engineering.Near-fault ground motion field distribution not only provides an input motion but also provides the range of avoiding belt of the foundation in seismic design.Based on regional geological structure,activity assessment of aimed fault and assessment of seismic hazard,using experience statistical relationship to determine seismogenic faults,the corresponding source model was set up.Combining 3-D finite element analysis and parallel computing,the long period ground motions were calculated.The method of limited-fault random synthesis was used to calculate the high frequency ground motion.The high-frequency and low-frequency ground motions were composed to broad-frequency ground motion.1-D equivalent linearization method was used to calculate the broad-frequency ground motion time histories of some special local sites according to survey data.The PGA distribution and the corresponding response spectra of the target region are got according to the ground motion time histories when the design earthquake occurs.As an example,the near-fault ground motion distribution of Changchun City was predicted when a setting earthquake occurred.When an Ms6.0 earthquake occurs on the Jianshanzi-Kalun fault,the influence range of potentially destructive ground motion is near the fault,and the distribution of influence range is along the fault.The peak acceleration varies along the fault vertically mainly from 90 Gal to 140 Gal and the peak acceleration reaches 200 Gal only in the southern part of Changchun City.The forecasting result has the basic characteristics of near-fault ground motion,and matches the current basic understanding of the ground motion near the fault.