ESTIMATION OF MOMENT RELEASED DISTRIBUTION FOR 2003 BAM EARTHQUAKE BY INVERSION OF STRONG MOTION DATA

We invert 3-component near field accelerograms recorded by BHRC strong-motion network to obtain the complete rupture history and slip distribution for Bam earthquakes (December 26, 2003) that occurred on nearly NS striking and dip down right-lateral strike-slip fault. ccelerograms are band-pass filtered with 0.01-1 Hz, and the 10-20 s of the seismograms are inverted. The lack ofabsolute timing has been successfully overcome by estimating the propagation of P waves in a detailed structural model. Our goal is to determine the spatial and temporal distribution of seismic moment and slip over the fault area. By dividing the fault into square cells and the source time function into steps the problem can be discredited and assumes the form of a system of linear equation. For considering the path effects, the Green functions are determined using the multimodal summation method for layered, an elastic medium and they are computed for a maximum frequency of 1 Hz. The extended fault is modelled as a grid of point sources, and the synthetic seismogram at each station due to the moment release on the fault is computed by summing the contribution from each point source with appropriate delays and weights. To solve the constrained linear system, we used the method of linear programming in which the vector of the residuals is minimized. The results for Bam earthquake are supported quantitatively by the well values, which guarantee also for a satisfactory waveform fit for stations <60 km, and by the synthetic tests. The synthetic tests carried out for a linear programming problem of the dimension equal to that of our real inverse problem allow us to conclude that the obtained results can be considered appreciable with a resolution of at least 3km×3km. The final fault model and source parameters are in good agreement between the synthetic and the observed waveforms especially in Bam station.

Keywords:

Bam Earthquake , Strong Motion Inversion , Source Parameters , Synthetic Test