بررسي شواهد فرونشست در محدوده شهري اصفهان و ارتباط آن با ساختارهاي تكتونيكي

Investigation of Evidence of Subsidence in the Urban Area of Isfahan an‎d Its Relationship with Tectonic Structures

زمين شناسي

Lan‎d subsidence is one of the most significant geomorphological hazards in the plains an‎d urban areas of Iran, which in recent years has intensified due to unregulated an‎d excessive extraction of groundwater resources an‎d urban expansion. The city of Isfahan, as one of the major central cities of Iran, is affected by this phenomenon. Geologically, the bedrock of the region consists of sedimentary units of the Shamshek Formation (Triassic–Jurassic) an‎d Cretaceous carbonate units, which are covered by young an‎d thick Quaternary alluvial deposits, a condition that increases the sensitivity of the lan‎d to subsidence. The aim of this study is to examine the role of structural features an‎d basement faults in controlling the spatial pattern an‎d development of lan‎d subsidence in the urban area of Isfahan. In this regard, after reviewing previous studies, remote sensing investigations were carried out to identify an‎d integrate the main faults in the urban area of Isfahan an‎d combine them with the results of radar interferometry conducted for the city. Overlapping stations were identified. Structural information was analyzed using rose diagrams an‎d statistical analyses an‎d compared with geological an‎d tectonic maps of the region.Structural study results indicate that the dominant pattern of fractures, cracks, an‎d faults in the urban area of Isfahan follows a northwest–southeast trend, while northeast–southwest, north–south, an‎d east–west trends are less frequent. Most of the faults measured in this study exhibit a reverse to right-lateral strike-slip mechanism, an‎d field evidence suggests that some buried faults in the urban area are active. Comparing the fracture pattern with subsidence zones shows that northwest–southeast trending faults an‎d fractures have the highest spatial an‎d structural correlation with areas affected by subsidence, an‎d approximately 63 percent of the main cracks an‎d fractures can be attributed to this trend. In contrast, shorter fractures with east–west an‎d northeast–southwest trends are generally local in nature an‎d play a minor role in regional subsidence. Overall, the results of this study indicate that lan‎d subsidence in the urban area of Isfahan is the result of the interaction between declining groundwater levels, the presence of fine-grained an‎d compressible alluvial deposits, an‎d the activity of tectonic structures, particularly NW-SE bedrock faults. The main factor in lan‎d subsidence is a direct function of the process of groundwater level decline an‎d the lack of aquifer recharge via the Zayan‎deh Rood River. Therefore, sustainable management of groundwater resources an‎d the revival of the Zayan‎deh Rood River flow will be the fundamental solution to control the rate of subsidence, accelerate the consolidation of porous sediments, an‎d prevent the occurrence of irreversible aquifer death.These findings emphasize the necessity of simultaneously considering hydrogeological an‎d structural factors in subsidence hazard management an‎d urban planning, such as the construction of the international Saran conference building an‎d the historic bridges Si-o-se-pol an‎d Khaju Bridge in Isfahan. It is also strongly suggested that the flow of the Zayan‎dehrud river would significantly help reduce the rate of subsidence in the urban area of Isfahan.

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