On 28 May 2004, a strong earthquake, Mw 6.5, occurred at Kojour area in northern part of Iran. During this earthquake a regional network of 146 strongmotion accelerograph stations equipped with SSA2 instruments located within 15-280 km range from the source registered the event with the PGA range from 0.9 to 0.03 g. A local magnitude of 6.4 was calculated from the synthesized Wood-Anderson records using 238 horizontal components. To estimate the source parameters, we selected the accelerograms recorded within 100 km from the epicenter and we employed different conventional methods and compared the inferred results. The estimate of Mo, given by the Brune's model and by the objective 10 seconds duration (Andrews, 1986) is about 3.00E25 dyne-em with no noticeable azimuthal dependency. This givesMw 6.2, that is the same as the value of the moment magnitude reported by the telemetric data. Estimates of the stress drop by the three methods of Brune, objective, and arms (Hanks and McGuire, 1981) are respectively 115, 230, and 66 bars with large standard deviations. The geometrical average of the corner frequency, fc, is 0.24 Hz with rather small variation. The parameters of stress drops, seismic energies, and the ML magnitudes evaluated from the selected records show strong azimuthal dependencies. Thevalues show noticeable increase beyond an azimuth of about 230 degrees from the epicenter. The Ms estimated from the geometrical average of the calculated energy is 6.5.

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