Constraint on the active tectonics of the Alborz using geodetic

Articles in Press

Document Type : Research Article

Authors

1 Department of Earth Sciences , Institute for Advanced Studies in Basic Sciences

2 Faculty of Engineering University of Zanjan

3 Department of Earth Sciences , Institute for Advanced Studies in Basic Sciences, Zanjan, Iran

Abstract

In this research, the deformation pattern of Alborz is investigated using a combination of data from the new permanent GPS networks belong to State Organization for Registration of Deeds and Properties (SHAMIM) and Tehran Municipality (SAMT), the new temporary IASBS_NCC network and data from the permanent and temporary stations of the National Cartographic Organization. The addition of the 27 new GPS stations has improved the obtained velocity field, which shows that the active deformation happens across the entire width of Alborz from south to north by several faults and active fault zones. Contrary to the common belief about the strain partitioning in the Alborz mountains between the strike-slip faults in the southern flank of Alborz and along the compressional south-dipping Khazar fault in the northern flank of Alborz, the new velocity field indicates a spread of strike-slip and compressional movements along different faults across the width of the Alborz. In previous works, due to the lack of GPS stations between the Khazar fault and other active faults in the northern flank of Alborz (e.g. North Alborz fault), all the observed deformation in the northern flank of Alborz has been associated with the Khazar fault. In the improved velocity field, the presence of a new GPS vector between the North Alborz and the Khazar faults in the eastern part of Alborz indicates a dominant role of the North Alborz fault in the strain accommodation once compared to the Khazar fault. Like the previous works, the new velocity field shows a lower total strain for the western Alborz, which is consistent with the lower observed seismicity in the western Alborz. The new velocity field indicates an active extensional system in the western Alborz in a longitude range of 49o to 50.5o around Tarom Valley. The extensional system might be related to the counterclock wise rotation of South Caspian Basin relative to Eurasia. The improved velocity field shows a noticeable strike-slip motion of 2 mm/yr at the northern edge of Central Iran which could be related to Aran-Torud fault zone and Attari fault. There is also a shortening rate of ~2 mm/yr between the northern edge of Central Iran and Eastern Alborz which could be related to the salt tectonic within the Great Kavir. The improved velocity field shows a right-lateral strike-slip motion of ~1 mm/yr across Indes and Kushk-Nosrat faults. Despite the observed large seismic activity and a geological slip rate of 2 mm/yr for the eastern part of the Mosha fault, both strike-slip and compressional slip rates along the Mosha fault are less than 1 mm/yr. Within a radius of ~50 km from the center of the Tehran metropolitan area, there is no noticeable rate of strike-slip or compressional movement and the strain rate is around the error limit or less than 1 mm/yr. The low strain rate implies a very long earthquake return period for large earthquakes in Tehran metropolitan area.

Keywords

Iranian Journal of Geophysics

Articles in Press, Accepted Manuscript
Available Online from 10 December 2023

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