Archaeoseismicity of the Mounds and Monuments along the Kāzerun Fault (Western Zāgros, SW Iranian Plateau) since the Chalcolithic Period

Abstract

Our multidisciplinary investigation represents off-fault archaeoseismic indicators recorded in the archaeological remains at mounds and structural elements of monuments situated along the Kāzerun fault in the western Zāgros Mountains since the Chalcolithic period. The study revealed two large magnitude earthquakes (~Mw > 7.0, possibly ~7.3) ca. 3850-3680 BC and ca. 3030 BC with return periods of ~735 ± ? years at Tol-e Spid. Detecting only two earthquakes during the 4000 year life span of archaeological mound is incompatible with the 3.6-3.9 slip rate along the Kāzerun fault. After a long gap in data, a strong earthquake indicator is recorded ca. 400-200 BC in Qal'eh Kāli; all located to the north of the Kāzerun fault bend. On the contrary, in addition to the vandalism episodes during the invasions of the Moslem Arabs (16/637), the Mongol hordes (1219-1250), and Timur (1370-1405), the structural elements of the royal Sasanid city of Bishāpur, located to the south of the fault bend, indicated archaeoseismic indicators of four possible earthquakes within a period of 800 years. The limited data indicate that the archaeological sites located to the north of the fault bend (Tol-e Spid, Tol-e Nurābād, Qal'eh Kāli, Tal-e Gachgaerān, Mil-e Ezhdehā, and Naubandégān) were subjected to stronger (larger magnitude) earthquakes with longer return periods. Whereas the sites located to the south of the fault bend (Sasanid royal city of Bishāpur and Kāzerun) showed evidence of earthquakes with slightly lower magnitudes and shorter recurrence periods of ~270 ± ? years. The study has shed light on the approximate magnitude and return period of earthquakes which could not have been achieved through the short term regional historical earthquake records. The distribution of settlements from the Chalcolithic to the present in closely associated with the trend of the Kāzerun fault. The archaeoseismic events in the past were disasterous to urban areas and the fault constitutes a continuing hazard to the local population and their irreplaceable monuments.