The occurrence of the western Iran earthquake of 31 March 2006 provided an important
opportunity to study the source properties of earthquakes in this region. Although moderate
in size (ML = 6:1, IIEES), this earthquake was the largest to have occurred in the region since
the deployment of the Global Digital Seismograph Network. The far- eld data determination of
body wave (P) spectra, interpreted in terms of the circular seismic source model, are used to
estimate the parameters seismic moment (MO), corner frequency (f0) , source radius (r) and
stress drop (). P waves recorded at teleseismic distances can be obtained from stations of
this network that are
at to displacement, in a frequency range of 0.19 to 0.32 Hz. The average
seismic moment (MO = 14:92 1019 N-M) and source radius (r = 9281 m) were calculated
from the long period spectral levels, which were corrected for the radiation pattern of a double
couple point source. In addition, the stress drops ( = 87106 N/m2) of this event have been
calculated by using an average seismic moment and source radius. Additional errors in the stress
drop determination are produced by uncertainty in the seismic moment. Scatter in the seismic
moment values is caused by such factors as site condition and errors in the radiation pattern.
)