Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
Iran is an active continental domain accommodating the convergence between the Arabia and Eurasia plates. In northwestern Iran, deformation between the Central Iranian block and the Caucasus domain is mainly accommodated by right lateral strike-slip on the Tabriz fault. Cities and villages, including the city of Tabriz, have been destroyed by several strong historical earthquakes (M similar to 7). In this study, we compare the slip-rates estimated from geodetic measurements (radar interferometry and UPS) with those determined by dating a geomorphological offset of an alluvial fan along the Tabriz fault. The GPS measurements along two profiles normal to the Tabriz fault suggest a slip-rate of 7.3 +/- 1.3 mm yr(-1). The persistent scatterer radar interferometry analysis of Envisat satellite archives from 2003 to 2010 shows a velocity gradient (6 +/- 3 mm yr(-1)) across the Tabriz fault in agreement with GPS results. Moreover, it reveals that most of the area located south of the Tabriz fault is affected by subsidence, and that some sections of the fault probably act as barriers to fluid migration which may have an impact on its mechanical behaviour. West of Tabriz morphotectonic investigations on an alluvial fan surface show a right-lateral cumulative offset of 320 +/- 40 m Luminescence analyses of the coarse matrix alluvial fan deposits provide an age of 46 +/- 3 ka. This yields a slip-rate comprised between 6.5 and 7.3 mm yr(-1) along this segment. These results suggest that the Late Quaternary slip-rate is in agreement with the present-day slip-rate estimated by geodetic measurements, showing no slip-rate changes during the past 45 000 yr. Short-term variations within the 45 000 yr related to temporal earthquake clustering over few seismic cycles cannot be ruled out, but if they exist, they do not affect the geodetic and the geomorphological estimates. This study is in agreement with previous ones suggesting that long-term slip-rates (i.e. averaged over several tens of seismic cycles) are consistent with geodetic estimated slip-rates (i.e. extrapolated from few years of interseismic observations), and suggests that perturbations of fault slip-rates are related to variations over few seismic cycles.
ISSN: 0956-540X

hal-00844695
https://hal.archives-ouvertes.fr/hal-00844695
https://hal.archives-ouvertes.fr/hal-00844695v2/document
https://hal.archives-ouvertes.fr/hal-00844695/file/rizza2013.pdf
DOI : 10.1093/gji/ggt041

Éditeur(s) : HAL CCSD
Résumé : The Astaneh fault with a length of more than 75 km is located in NW of Damghan. Morphotectonic investigation along the Astaneh fault and left - lateral displacement in quaternary deposits shows that, Astaneh is an active fault. It is necessary to recognize paleoseismicity of Astaneh fault because, this fault is located in seismic zone of Komes historical earthquake with Ms=7.9 (Ambraseys & Melville, 1982). Many people (more than 45000) were killed in Damghan city in Komes historical earthquake. In this paper, 4-5 paleo events along the Astaneh fault are presented through paleoseismological investigation.
Geosciences Scientific Quarterly Journal

hal-00854396
https://hal.archives-ouvertes.fr/hal-00854396

Éditeur(s) : HAL CCSD
Résumé : The Firouzkuh Fault in most of its extension is located at the southern side of Firouzkuh Valley in west of the Central Alborz. It is a SW - NE prominent structure with a 70 km long on a sinistral -normal fault. It has been known as a south-dipping reverse fault.Paleoseismic analysis and C14 dating along the Firouzkuh left -lateral strike-slip fault indicate that Central Alborz has been shaken by large earthquakes during the Holocene. Here we present the data carried out of one of the two excavated trenches with 15 m long, 2m wide, ~ 4m deep in the east of Firouzkuh, where we found some evidence for last paleoearthquake associated to seismic re-activity on Firouzkuh Fault in the second trench (F2) that dug across a gauge zone. The last event is evidenced by cutting young superficial deposit where this faulted unit stratigrafically covered alluvium deposits yielded dated human bones fragments. The bones found in 60-70cm-deep of trench which a C14 age of 1159 ± 28 BP. Regarding to estimated slips per event on paleoseismological log of eastern wall of trench F1, event magnitudes for each paleoearthquakes are M≈7.
Geosciences Scientific Quarterly Journal

hal-00800375
https://hal.archives-ouvertes.fr/hal-00800375

Éditeur(s) : HAL CCSD
Résumé : Neotectonics in Central Alborz
Geosciences Scientific Quarterly Journal

hal-00809626
https://hal.archives-ouvertes.fr/hal-00809626

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
The North Tehran Fault (NTF) is located at the southernmost piedmont of Central Alborz and crosses the northern suburbs of the Tehran metropolis and adjacent cities, where ∼15 million people live. Extending over a length of about 110 km, the NTF stands out as a major active fault and represents an important seismic hazard for the Iranian capital after historical seismicity. In order to characterize the activity of the NTF in terms of kinematics, magnitude and recurrence intervals of earthquakes, we carried out a first paleoseismological study of the fault within its central part between Tehran and Karaj cities. We opened a trench across a 3 m-high fault scarp affecting Quaternary deposits. Our study shows that the scarp is the result of repeated events along a main N115°E trending shallow dipping thrust fault, associated with secondary ruptures. From the trench analysis and Infrared Stimulated Luminescence (IRSL) dating of fault-related sediments, we interpreted between 6 and 7 surface-rupturing events that occurred during the past 30 kyrs. Their magnitudes (estimated from the displacements along the faults) are comprised between 6.1 and 7.2. The two last events - the largest - occurred during the past 7.9 ± 1.2 ka, which yields a Holocene slip rate of ∼0.3 mm/yr. The 7 earthquakes scenario suggests a regular periodicity with a mean recurrence interval of ∼3.8 kyrs. However, the two most recent events could correspond to the two largest historical earthquakes recorded in the area (in 312-280 B.C. and 1177 A.D.), and therefore suggest that the NTF activity is not regular.
ISSN: 0148-0227

hal-00757568
https://hal.archives-ouvertes.fr/hal-00757568
https://hal.archives-ouvertes.fr/hal-00757568v2/document
https://hal.archives-ouvertes.fr/hal-00757568/file/ritz2012.pdf
DOI : 10.1029/2012JB009147

Éditeur(s) : HAL CCSD
Résumé : Neotectonics in Central Alborz
Geosciences Scientific Quarterly Journal

hal-00811586
https://hal.archives-ouvertes.fr/hal-00811586

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
The 856 A.D. Qumis earthquake (M7.9) is the most destructive earthquake to have occurred in Iran, killing more than 200,000 people and destroying the cities of Damghan and the old Parthian capital of Shahr-i Qumis (Hecatompylos). This study combines evidence of historical seismicity with observations of the geomorphology and paleoseismology to provide the first detailed description of active faulting in the Damghan region of the east Alborz mountains, Iran. Regional left-lateral shear is accommodated on the Astaneh, Damghan, and North Damghan faults. Quaternary alluvial fans have been displaced along the Astaneh fault, with 15–20 m stream offsets recording the cumulative displacement over the last two to five earthquakes. A paleoseismology study from a single trench along a 5–10 km segment of the Astaneh fault reveals a rupture prior to 1300 A.D. and significantly later than 600 B.C. Despite the limitations of a single trench in documenting the spatial and temporal evolution of the fault over the late Quaternary, we are nevertheless able to bracket the last event to a time period consistent with the 856 A.D. earthquake. Two older earthquakes were also identified during the Holocene occurring between 600 B.C. and 4600 B.C. and between 4600 B.C. and 9600 B.C. The location of our trench within a bend on the Astaneh fault, which could act as a barrier to rupture propagation, means the three earthquakes recovered from our trench over the Holocene may represent a minimum. Further trenching will reveal how the Astaneh fault ruptures over repeated earthquakes and, consequently, the magnitude and extent of slip during the 856 A.D. earthquake.
ISSN: 0148-0227

hal-00551330
https://hal.archives-ouvertes.fr/hal-00551330
https://hal.archives-ouvertes.fr/hal-00551330v2/document
https://hal.archives-ouvertes.fr/hal-00551330/file/Hollingsworth2010.pdf
DOI : 10.1029/2009JB007185

Éditeur(s) : HAL CCSD
Résumé : Neotectonics in Central Alborz
Geosciences Scientific Quarterly Journal

hal-00809627
https://hal.archives-ouvertes.fr/hal-00809627