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

Abstract

“…King Ardeshir Babakan Sassanid [r. AD 224-241], by conquering Kerman and Bam, killed the ‘Kerm-e-Haftvad’ [the Haftvad Silk Worm] at the Bam Citadel. The gigantic worm burst with a big bang noise, which rocked the area, completely destroyed the Bam Citadel, and killed most of the inhabitants of the Citadel. King Ardeshir put an end to the rule of governor Haftvad, built the new village of Kolalan/Kojaran [Kurzan; the old Deh Shotor quarter in west Bam], and brought the ‘seven sacred fires of Bahram’ to the new village…”

[Book of Deeds of Ardashir Pabagan 1878 (English Tr., original version ca. AD 272); Tabari 915; Ferdowsi Tusi 1010; & Mostaufi Qazvini 1340. The entire episode rests on the rationalization of historical events of unknown nature, and perhaps the legendary element could be a possible, mixed metaphoric reference to a ‘destructive earthquake’ or even a ‘conquering battle’ against the ancient city of Bam and its Parthian governor, Haftvad!]

The impact of the Bam urban earthquake of 26 December 2003 ( _Mw 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 large- magnitude 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 strike-slip 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.