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In this paper, we use satellite images, field observations and aeromagnetic data to describe major tectonic features in the central portion of the Urumieh-Dokhtar Magmatic Arc (UDMA) in Central Iran. Most of the analyzed structures such as horsetail splays, rotated blocks, positive flower structures and sedimentary basins have not been previously recognized. The NW-SE-trending Zefreh Fault is the most important dextral transpressional active lineament in the area. Maps of filtered aeromagnetic anomalies confirmed that the fault also affects the basement. Based on our field observations and cross-cutting relationships, tectonic evolution of the central part of the UDMA is interpreted in terms of two main stages:(1) formation of main thrusts during shortening and exhumation of older rocks in the UDMA after Eocene-Oligocene, and (2) transpressional movements reactivating the main thrust faults to reverse-dextral strike-slip faults during the Pliocene-Quaternary. The present-day deformation of the UDMA is mostly dominated by strike-slip movements. These two stages are interpreted as reflecting a change in convergence vector between Arabian and Eurasian plates.

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Based on the data from piezometers, well logs, geophysical surveys and the interferometric synthetic aperture radar (InSAR) technique, this study investigates the main causes of land subsidence in Damaneh City, Iran. The size, openings and direction of fissures were measured by micrometer and compass. The locations of fissures and wall cracks were determined by GPS. The geoelectrical data were used to determine the composition, thickness, depth and shape of lower parts of the aquifer. Groundwater fluctuations were evaluated by available piezometers. The InSAR technique was used to measure land deformation from space and to map the dense changes of surface displacements. The results indicate that the main cause of ground subsidence is the decline of groundwater heads and changes in composition and thickness of compressible lacustrine sediments. The subsidence map obtained from the radar data of ASAR sensor of ENVISAT satellite shows that the subsidence zone is mainly in northern city that is underlain by very thick fine sediments. The subsidence rates from March to December 2005 and from July 2011 to January 2012 are 6.7 and 7.0 cm/a, respectively. The results also show good correlations among the formation of earth features, decline in groundwater head and thickness of fine-grained sediments. We recommend that the groundwater withdrawal for agricultural and industrial sectors should be restricted and urban expansion in the northern part of the city should be constrained.

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