The 2003 Bam Urban Earthquake: A Predictable Seismotectonic Pattern Along the Western Margin of the Rigid Lut Block, Southeast Iran

The impact of the Bam urban earthquake of 26 December 2003 (M-w 6.6 ) was far more devastating than that which would be expected from a moderate magnitude earthquake. The event followed a predictable geological/ seismological pattern of a specially clustered sequence of medium- to largemagnitude earthquakes on tectonically related active faults in a region with historic slip deficits along the western margin of the rigid Lut block. The earthquake was accompanied by the coseismic rupture of sub-parallel strikeslip faults in a zone revealing a pattern of temporal clustering of seismicity, loading of adjacent faults, and a southwards progressing trend of earthquakes from the Kuh Banan to the Gowk and the Bam fault systems. As with the Agadir, Morocco, earthquake of 1960, and the great Tangshan, China, earthquake of 1976, the Bam urban earthquake painfully demonstrated the growing vulnerability of a city built on or adjacent to a seismic fault, unprepared to be tested by the severe ground motion triggered by a medium magnitude earthquake. The absence of historical seismic records regarding the occurrence of earthquakes in the region or the lengthy time spans between such disasters has been erroneously interpreted as a lack of any potential threat for the last 2,500 years in the city of Bam.