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Theses

Active tectonics and paleoseismology of strike-slip faults of Central Iran

Abstract : The Central Iran plateau is experiencing very low GPS deformation rates and appears aseismic during the last few millennia. Nevertheless, it is sliced by several N-striking, right-lateral, strikeslip faults that are hundreds of kilometers long. The slip rate and seismic behavior of three of these faults (from west to east: Dehshir, Anar, and Nayband) have been investigated throughout this dissertation. The paleoseismic records along the 380-km long, Dehshir fault demonstrate the occurrence of at least three large (Mw ≈ 7) earthquakes during the last 22 ka, the most recent event occurring shortly before ∼2 ka. Additional observations yield a slip rate between 0.9 and 1.48 mm yr-1 over the last 42 ka, which agrees with the previous slip rate of 1.2 ± 0.3 mm yr-1 averaged over the last 270 ka. This suggests that the slip rate has remained constant during the late Pleistocene and Holocene. The paleoseismic study on the 200-km long, Anar fault shows that three large earthquakes occurred at 4.4 ± 0.8, 6.8 ± 1, and 9.8 ± 2 ka. The age of the most recent event (3.6-5.2 ka) suggests the fault is approaching the end of its seismic cycle. These results confirm a previous minimum slip rate of 0.8 ± 0.1 mm yr-1 for the Anar fault, indicating that the westernmost prominent faults of Central Iran are characterized by slip rates close to 1 mm yr-1. The slip rate on the 290-km long, Nayband fault is determined using cosmogenic and optically stimulated luminescence dating of cumulative offsets. The offsets range between 9 ± 1 m and 195 ± 15 m with ages from 6.8 ± 0.6 ka to ∼100 ka, yielding a slip rate of 1.8 ± 0.7 mm yr-1. The first paleoseismic record demonstrates the occurrence of at least four large earthquakes during the last 17.4 ± 1.3 ka and two older events (before ∼23 ka and 70 ± 5 ka). Penultimate and antepenultimate events occurred between 6.5 ± 0.4 and 6.7 ± 0.4 ka, whereas the most recent event took place within the last 800 years. Such an irregular earthquake occurrence suggests seismic clustering. Although the most recent earthquakes on the Nayband and Dehshir faults occurred after AD 1200 and shortly before ∼2 ka, respectively, these events went unnoticed in the historical seismic records. These are marked illustrations of the incompleteness of the historical seismic catalogs in Central Iran, challenging any seismic hazard assessment without geologic information. The paleoseismic records show that Central Iran does not behave totally as a rigid block and that its moderate internal deformation is nonetheless responsible for a significant seismic hazard. Thus, large infrequent earthquakes typify the slow-slipping strike-slip faults slicing Central and Eastern Iran, which slip rates summed from the Iran Plateau up to the Afghan lowlands remain difficult to match with the available GPS data.
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https://tel.archives-ouvertes.fr/tel-00922358
Contributor : Mohammad Foroutan <>
Submitted on : Thursday, December 26, 2013 - 10:57:11 AM
Last modification on : Wednesday, December 9, 2020 - 3:10:10 PM
Long-term archiving on: : Friday, March 28, 2014 - 4:55:17 PM

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  • HAL Id : tel-00922358, version 1

Citation

Mohammad Foroutan. Active tectonics and paleoseismology of strike-slip faults of Central Iran. Earth Sciences. Université Pierre et Marie Curie - Paris VI, 2013. English. ⟨tel-00922358⟩

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