The 2003 Bam, Iran, Earthquake: An Interpretation of the Strong Motion Records

On 26 December 2003, a destructive earthquake occurred in southeastern Iran, demolishing the city of Bam and vicinity. The highest intensity of shaking (VIII-IX) was observed in the city of Bam. The source of this shock was reported to have had a right-lateral strike-slip mechanism initiated in a blind fault in the north-south direction. A regional network consisting of 23 strong motion stations (SSA-2 Accelerograph), located within 1-290 km from the epicenter, registered the earthquake. The compact and pulse-shape arrivals of strong signals recorded at the Bam station strongly suggest that the rupture was initiated south of the city and propagated toward Bam. Based on the relative arrival times of the rupture front and the arrivals of P and S waves at this station, the velocity of rupture was estimated as 2.5 +/- 0.2 km/sec. Comparisons made between the attenuation curves constructed for this earthquake and those of the regional curves show that the effects of directivity caused significant deviations at near distances from the fault. This strong motion data yields estimates of source parameter values of 8.3 x 0(25) (dyne -cm), 7.5 km, and 90 bars, respectively, for seismic moment, source radius, and stress drop.