Archaeoseismicity of the Mounds and Monuments Along the Kazerun Fault (Western Zagros, Sw Iranian Plateau) Since the Chalcolithic Period
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Iranica Antiqua, vol. XLIX, 2014 doi: 10.2143/IA.49.0.3009238 ARCHAEOSEISMICITY OF THE MOUNDS AND MONUMENTS ALONG THE KAZERUN FAULT (WESTERN ZAGROS, SW IRANIAN PLATEAU) SINCE THE CHALCOLITHIC PERIOD BY Manuel BERBERIANa , Cameron A. PETRIEb, D.T. POTTSc, Alireza ASGARI CHAVERDId, Amanda DUSTINGe, Alireza SARDARI ZARCHIf, Lloyd WEEKSg, Parsa GHASSEMIh & Reza NORUZIi (a Ocean County College, USA; b University of Cambridge, UK; c ISAW, NYU, USA; d Shiraz University, Iran; e University of Sydney, Australia; f Iranian Center for Archaeological Research, Iran; g University of Nottingham, UK; h Kohan Diar-e Mehr Archaeological Inst., Shiraz, Iran) Abstract: Our multidisciplinary investigation represents off-fault archaeoseismic indicators recorded in the archaeological remains at mounds and structural ele- ments of monuments situated along the Kazerun fault in the western Zagros 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 4,000 year life span of archaeological mound is incompatible with the 3.6-3.9 slip rate along the Kazerun fault. After a long gap in data, a strong earth- quake indicator is recorded ca. 400-200 BC in Qal’eh Kali; all located to the north of the Kazerun 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 Bishapur, 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 Nurabad, Qal’eh Kali, Tal-e Gachgaeran, Mil-e Ezhdeha, & Naubandégan) 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 Bishapur and Kazerun) 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 earth- quakes which could not have been achieved through the short term regional his- torical earthquake records. The distribution of settlements from the Chalcolithic to the present in closely associated with the trend of the Kazerun fault. The archaeoseismic events in the past were disasterous to urban areas and the fault 96550.indb 1 25/02/14 13:48 2 MANUEL BERBERIAN ET AL. constitutes a continuing hazard to the local population and their irreplaceable monuments. Keywords: Archaeoseismicity, Kazerun active fault, Tol-e Spid, Tol-e Nurabad, Qal’eh Kali, Naubandégan, Mil-e Ezhdeha, Bishapur, Kazerun, Zagros, Iran I. Introduction The Zagros mountain range of the southwestern Iranian plateau is one of the Earth’s most seismically-active fold-and-thrust mountain belts (Fig. 1). At present, it is marked by rapid deformation in the form of active folding and uplifting as well as active basement and surface faulting (Berberian 1995; Mouthereau et al. 2012). The Zagros is characterized by NW-SE trending longitudinal folds and reverse faults, and nearly N-S transverse right-lateral strike-slip active faults cutting the former structures (Berberian 1995). The belt accommodates about 8 mm/yr of the 25 mm/yr total N-S crustal shortening of the Iranian plateau between Arabia and Eurasia at about longitude ~53oE (Tatar et al. 2002; Vernant et al. 2004; Walpersdorf et al. 2006) (fig. 1). The post-1900 seismicity in the Zagros is dispersed and the pre-1900 earthquake data are incomplete and inhomogene- ous (Table 1) (Ambraseys & Melville 1982; Berberian 1981, 1994 & 1995). The Zagros, the Alborz, and the Kopeh Dagh fold-and-thrust mountain belts (fig. 1 and 2) all have high annual rainfall, abundant arable lands, large braided perennial rivers, and numerous natural karstic and/or fault springs. Archaeological research has shown that each of these belts sup- ported numerous ancient settlements at least from the early Neolithic period onwards. Furthermore, ancient settlements in the semi-arid to arid parts of the tectonically-active Central Iranian plateau were located on lim- ited arable lands with fault-controlled secure water supplies along a num- ber of mountain-bordering reverse and strike-slip faults, which were suit- able for use as passageways through the mountains during prehistory. There is a lack of palaeoseismologic trench studies across the active surface faults of the Zagros, but archaeological data have the potential to offer insight into the long-term seismicity and expand our knowledge of the temporal and spatial distribution of ancient earthquakes. If archaeological records are carefully investigated and integrated with historical seismic and fault data, the earthquake records of regions will be extended, and this will ultimately improve the capacity for seismic hazard assessment. 96550.indb 2 25/02/14 13:48 ARCHAEOSEISMICITY ALONG THE KAZERUN FAULT 3 Fig. 1. (a) Seismicity of Iran 1964–98, from the catalogue of Engdahl et al. (1998). The Zagros Mountains in the SW are marked by Z, the Alborz Mountains in the north by A, the Kopeh Dagh by K, and the Sistan region by S. (b) Map of Iran showing GPS velocity points relative to Eurasia (Vernant et al. 2004). The GPS velocities decrease to zero at both the northern (Kopeh Dagh) and eastern (Sistan) margins of Iran, suggesting that the Arabia-Eurasia convergence is accommodated within the political borders of Iran. Most of the active deformation occurs in the seismically active Zagros (in the SW and S), Alborz (north, south of the Caspian Sea) and Kopeh Dagh (NE) Mountain. The study area along the Kazerun fault is located to the immediate south of letter Z in the Zagros. A number of medium- to large-magnitude earthquakes have devastated ancient Iranian monuments and archaeological sites that were built adja- cent to active faults. These events would have affected ancient civiliza- tions, constrained patterns of settlement, and ultimately have had long-term social and cultural impacts (Berberian 1994; Berberian & Yeats 2001; Berberian et al. 2012). The main purpose of this paper is to examine archaeological and archi- tectural data from some excavated archaeological sites that are located adjacent to the active Kazerun transverse fault in the western Zagros (fig. 1 and 2), in order to evaluate possible traces of the effects of ancient earthquakes. We combine interpretation of the prehistoric archaeological record and architectural deformation with evidence for historically docu- mented earthquakes, old chronicles, and geological, morphological and seismological data to correlate ancient earthquake indicators visible at 96550.indb 3 25/02/14 13:48 4 MANUEL BERBERIAN ET AL. Fig. 2. Location of the study area along the Kazerun active right-lateral strike-slip fault in the Zagros fold-and-thrust mountain belt of the southern Iran (marked by a box) in the context of the major active faults of Iran (fault names in italics). Reverse faults are shown with teeth on hanging wall side. Strike-slip faults shown with arrows (after Berberian & Yeats 2001; Berberian 2005). Archaeoseismic sites discussed in this paper (Table 5) are shown by filled triangles (AT: Ak Tapeh; B: Bishapur; M: Mithradatkart, modern Nesa; TS: Tol-e Spid, Qal’eh Kali, & Tol-e Nurabad; Marlik; Sagzabad; Sialk; and Qa’en). Inset top right: Map of Iran showing different structural belts, AZ: Azarbaijan; KP: Kopeh Dagh fold-and-thrust mountain belt; MA: Makran accretionary wedge; S: Sistan suture zone; and TP: Turan Plate. The Zagros fold-and-thrust mountain belt is located to the SW of the country. 96550.indb 4 25/02/14 13:48 ARCHAEOSEISMICITY ALONG THE KAZERUN FAULT 5 archaeological sites with their source faults in the study area. This is an important issue in seismic risk evaluation of this part of Iran, where no pre-1824 earthquakes have been documented in the available historical text corpus (Table 1). In order to execute this difficult task we have to review the archeological data focusing on archaeoseismic indicators and foot-prints hidden in archaeological mounds and buildings, as well as his- toric photographs taken during excavations. We hope the paper will make archaeologists, seismologists, and earth- quake geologists working in the greater Near East more aware of these issues. As discussed below, the archaeological evidence of strong ground motion is oftentimes sufficient to conclude that there were indeed instances when damage, destruction, and deformation were indeed earthquake- induced and not solely a result of anthropogenic or meteorological pro- cesses, such as erosion, leaching or weathering of archaeological deposits. The data expands our knowledge of the activity of the Kazerun fault, ena- bles a better understanding of the periodicity of earthquakes, improves our assessment of seismic hazard in the region, and helps mitigate seismic risks for the present population living in the nearby towns and villages (e.g. Yasuj, Nurabad, Kazerun, Borazjan, Ahram, and Khormuj). It may also help preserve the cultural heritage of the area (the Sasanid city of Bishapur, Mil-e Ezhdeha, etc.) from future earthquake damage. The excavations carried out at the Mamasani archaeological sites were limited in scope and the observations presented here were based on archae- ological deposits exposed in small soundings, often excavated deep into the stratigraphic deposits. The early excavations at the Sasanid city of Bishapur were limited to the 1930s knowledge and observation, and some of the later excavations were not systematic or conclusive. None of the excavation expeditions included archaeoseismicity in the project. The reac- tion of the ancient inhabitants of the region to the devastating earthquakes identified below is not clearly known.