| Abstrakt: |
In this research, the deformation pattern of Alborz is investigated using a combination of data from the new permanent GPS networks that belong to State Organization for Registration of Deeds and Properties (SHAMIM) and Tehran Municipality (SAMT), the new temporary IASBS_NCC network and 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 the Alborz and along the compressional south-dipping Khazar fault in the northern flank of the 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 the Alborz (e.g. North Alborz fault), all the observed deformation in the northern flank of the 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 fault in the eastern part of the 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 the Tarom Valley. The extensional system might be related to the counterclock wise rotation of the 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 the 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 the Eastern Alborz which could be related to the salt tectonic within the Great Kavir fault. The improved velocity field shows a right-lateral strike-slip motion of ~1 mm/yr across the 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 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. [ABSTRACT FROM AUTHOR] |
