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Earthquake Hazards Program

Tectonic Summary

Magnitude 6.6 SOUTHEASTERN IRAN
2003 December 26 01:56:52 UTC

Preliminary Earthquake Report
U.S. Geological Survey, National Earthquake Information Center
World Data Center for Seismology, Denver

This earthquake occurred as the result of stresses generated by the motion of the Arabian plate northward against the Eurasian plate at a rate of approximately 3 cm/yr (about one inch per year). Deformation of the Earth's crust in response to the plate motion takes place in a broad zone that spans the entire width of Iran and extends into Turkmenistan. Earthquakes occur as the result of both reverse faulting and strike-slip faulting within the zone of deformation.

Preliminary analysis of the pattern of seismic-wave radiation from the December 26 earthquake is consistent with the earthquake having been caused by right-lateral strike-slip motion on a north-south oriented fault. The earthquake occurred in a region within which major north-south, right-lateral, strike-slip faults had been previously mapped, and the epicenter lies near the previously mapped, north-south oriented, Bam fault. However, field investigations will be necessary to determine if the earthquake occurred on the Bam fault or on another, possibly not yet mapped, fault. The December 26 earthquake is 100 km south of the destructive earthquakes of June 11, 1981 (magnitude 6.6, approximately 3,000 deaths) and July 28, 1981 (magnitude 7.3, approximately 1,500 deaths). These earthquakes were caused by a combination of reverse-motion and strike-slip motion on the north-south oriented Gowk fault.

 


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