A Study on the Seismic Source Parameters Based on the Strong Motion Displacement Spectra and Time- Histories in the Near-Field of the Earthquake Faults

General:
     The performed studies on the recorded strong motions in the near-field of the earthquake faults indicate the evident source effects. These effects are consisted of the existence of double corner frequencies, rise and rupture times (apparent rupture duration) and great amplitudes of displacements in the long periods on the horizontal components for the records obtained in the stations located in front of the rupture propagation. Meanwhile the explained effects may influence on the frequency content of the motions. In the present paper, we have selected and studied 10 strong motion records from the near-field of the earthquake faults of the earthquake occurred in the last 25 years in Iran and Turkey. The selection was performed based on the magnitude of the events and their distance to the fault. The results of the studies show the source effects i the Tabas earthquake of 1978 (Mw7.4), Manjil earthquake of 1990 (Mw7.3), Zanjiran earthquake of 1994 (Mw5.9) in Iran and Izmit, Kocael earthquake of 1999 (Mw7.4) and Kaynasli, Duzce earthquake of 1999 (Mw7. I) in Turkey. Based on these studies, the variation of rupture times between 2 to 10 seconds and the rise times between 0.8 and 2.85 seconds are evident for the earthquakes with the magnitudes of 5.9 to 7.4. This study show the importance of the near-field effects in the seismic resistant designs for the site located nearby the faults. This should be noted that the proper records are suggested to be applied for the designs in the mentioned conditions, since the great amplitude of the
displacements in the long periods for the horizontal component are expected earby the faults.