ABSTRACT Kinematic interaction of faults is an important issue for detailed seismic hazard assessments in seismically active regions. The Eastern Mosha Fault (EMF) and the North Tehran Fault (NTF) are two major active faults of the... more
ABSTRACT Kinematic interaction of faults is an important issue for detailed seismic hazard assessments in seismically active regions. The Eastern Mosha Fault (EMF) and the North Tehran Fault (NTF) are two major active faults of the southern central Alborz mountains, located in proximity of Tehran (population ~ 9 million). We used field, geomorphological and paleoseismological data to explore the kinematic transition between the faults, and compare their short-term and long-term history of activity. We introduce the Niknamdeh segment of the NTF along which the strike-slip kinematics of EMF is transferred onto the NTF, and which is also responsible for development of a pull-apart basin between the eastern segments of the NTF. The Ira trench site at the linkage zone between the two faults reveals the history of interaction between rock avalanches, active faulting and sag-pond development. The kinematic continuity between the EMF and NTF requires updating seismic hazard models for the NTF, the most active fault adjacent to the Tehran Metropolis. Study of offsets of large-scale morphological features along the EMF, and comparison with estimated slip rates along the fault indicates that the EMF has started its left-lateral kinematics between 3.2 to 4.7 Ma. According to our paleoseismological data and the morphology of the nearby EMF and NTF, we suggest minimum and maximum values of about 1.8 and 3.0 mm/year for the left-lateral kinematics on the two faults in their linkage zone, averaged over Holocene time scales. Our study provides a partial interpretation, based on available data, for the fault activity in northeastern Tehran region, which may be completed with studies of other active faults of the region to evaluate a more realistic seismic hazard analysis for this heavily populated major city.
Between 50-57°E shortening across the Arabian-Eurasian collision zone is accommodated primarily in the Zagros and Alborz mountains of Iran, which bound the relatively aseismic Central Iranian block. Both the lack of seismicity and the... more
Between 50-57°E shortening across the Arabian-Eurasian collision zone is accommodated primarily in the Zagros and Alborz mountains of Iran, which bound the relatively aseismic Central Iranian block. Both the lack of seismicity and the minor variation in GPS velocities across Central Iran suggest this region plays a negligible role in accommodating Arabia-Eurasia shortening at the present day. We examine recent
ABSTRACT Applications of luminescence dating of geological materials have undergone extensive development and refinement since 1974 when Wintle first attempted to date volcanic lava using thermoluminescence (TL). Today, luminescence... more
ABSTRACT Applications of luminescence dating of geological materials have undergone extensive development and refinement since 1974 when Wintle first attempted to date volcanic lava using thermoluminescence (TL). Today, luminescence techniques are potentially highly useful methods for dating volcanic and related materials and events over timescales ranging from 102 to 106 years. While luminescence approaches generally do not possess the precision afforded by techniques such as 40Ar/39Ar and 14C methods, they offer a useful alternative approach with advantages in terms of age range and scope of material. Although the application of luminescence methods has in some cases been successfully described, a comprehensive study outlining and defining protocols for routine luminescence dating of volcanic materials has not been forthcoming. This review surveys previous attempts to develop luminescence techniques to date volcanic products and discusses the state of knowledge of the luminescence behaviour of the four principal materials currently used for luminescence dating of volcanic events. Particular attention is paid to the red luminescence emissions, primarily because of previous successes in using Red Thermoluminescence (RTL) of quartz and feldspar for dating volcanic products, for which the upper age limit may extend beyond a million years. Proposals are made for future research directions; these include: technological developments in the measurement of optically stimulated red luminescence, the systematic characterization of RTL and optically stimulated red luminescence as key luminescence parameters in volcanic quartz, feldspar, glass and polymineral sample fractions, and optimization of luminescence dating methods to define a comprehensive protocol for routine dating of volcanic materials.
ABSTRACT We present ten infra-red stimulated luminescence (IRSL) ages of feldspar grains within lake-bed sediments and alluvial fan gravels displaced by the Gowk Fault, SE Iran. Our results show that lake deposition in the South Golbaf... more
ABSTRACT We present ten infra-red stimulated luminescence (IRSL) ages of feldspar grains within lake-bed sediments and alluvial fan gravels displaced by the Gowk Fault, SE Iran. Our results show that lake deposition in the South Golbaf basin was ongoing from at least 13.5 ka (the deepest exposed sediments) until the mid-Holocene. Furthermore, the South Golbaf palaeo-lake is likely to have spilled into the neighbouring Golbaf basin at 6.3 ± 0.2 ka. This event led to a widespread incision of the lake-bed and neighbouring alluvial fan surfaces as the drainage systems adjusted to the new base-level. Our constraint on the age of the South Golbaf palaeolake, combined with measurements of 30 ± 5 m of right-lateral displacement of stream channels incised into the lake-beds, yields a slip-rate of 3.8–5.7 mm/yr. The deposition of alluvial fans around the margins of the South Golbaf depression appears to have largely ended by 12.9 ± 0.7 ka. Right-lateral displacements of up to 60 m are observed in streams cut into the fan surfaces, yielding a second slip-rate estimate of ~ 4.4–4.9 mm/yr. Much of the widespread incision of the ~ 12.9 ka fan surfaces does not appear to have taken place until ~ 6 ka later, when overtopping of the South Golbaf palaeolake and the adjustment of drainage to a lower base-level, promoted widespread drainage incision.
... doi: 10.1111/j.1365-246X.2010.04538.x. Author Information. 1 Department of Earth Sciences, University of Oxford, Parks Road, Oxford, OX1 3PR, UK. E-mail: richard.walker@earth.ox.ac.uk. 2 Geological Survey of Iran, Azadi Square, Meraj... more
... doi: 10.1111/j.1365-246X.2010.04538.x. Author Information. 1 Department of Earth Sciences, University of Oxford, Parks Road, Oxford, OX1 3PR, UK. E-mail: richard.walker@earth.ox.ac.uk. 2 Geological Survey of Iran, Azadi Square, Meraj Avenue, PO Box 11365-4563, Iran. 3 ...
... Edwin Nissen 1 ,; Richard Walker 1 ,; Erdenebat Molor 2 ,; Morteza Fattahi 3,* ,; Amgalan Bayasgalan 2. ... 1996) and eastern Iran (Walker & Jackson 2004). ... the curly arrow shows the location of palaeomagnetic... more
... Edwin Nissen 1 ,; Richard Walker 1 ,; Erdenebat Molor 2 ,; Morteza Fattahi 3,* ,; Amgalan Bayasgalan 2. ... 1996) and eastern Iran (Walker & Jackson 2004). ... the curly arrow shows the location of palaeomagnetic measurements of anticlockwise rotations in the NW Altai (Thomas et al. ...
... Clear lateral displacements of alluvial fans are observed elsewhere along the fault, such as in the sections south of Bardsir (Fig. 3). ... A second zone of active strike-slip faulting cuts across the alluvial plains southwest of... more
... Clear lateral displacements of alluvial fans are observed elsewhere along the fault, such as in the sections south of Bardsir (Fig. 3). ... A second zone of active strike-slip faulting cuts across the alluvial plains southwest of Bardsir. ...
ABSTRACT A single-aliquot regeneration-dose red thermoluminescence (SAR RTL) protocol for heated quartz was introduced by Fattahi and Stokes (Radiat. Meas. 32 (2000) 479), which extended the time range of Luminescence dating. As there is... more
ABSTRACT A single-aliquot regeneration-dose red thermoluminescence (SAR RTL) protocol for heated quartz was introduced by Fattahi and Stokes (Radiat. Meas. 32 (2000) 479), which extended the time range of Luminescence dating. As there is a similar demand for extending the time range of non-baked sediments, we have tested SAR RTL for dating samples whose clocks have been reset by light. We have used two aliquots: one aliquot for De determination of natural and the other for De determination of unbleached components of TL. We have shown that all natural samples examined yield a detectable RTL signal, which is bleachable. The extent and rate of bleaching varies from sample to sample. Analysis of laboratory-irradiated samples demonstrates that the low-temperature peaks are more bleachable than high (>300 °C)-temperature peaks. The bleaching experiment further showed that bleaching of unheated quartz is more rapid than heated quartz. Our investigations of thermal pre-treatment suggests that a pre-heat of 330 °C for 10 s is sufficient to remove thermally unstable trapped charge and provide the similar RTL glow curve form for both regenerated and natural irradiation. We calculate an empirical characteristic saturation dose (D0) of 800 Gy for unheated quartz, which is 8 times less than previous estimates of D0 for volcanic quartz. This value is still 2 times greater than the typical values measured using blue optically stimulated luminescence (OSL). We apply our SAR RTL protocol to samples from various depositional environments (sand from UAE and USA; silt size loess from China). For the samples under study, test doses successfully monitor sensitivity changes resulting from laboratory dosing, pre-heating and thermal stimulation. Additionally, application of the SAR RTL protocol can successfully recover a known (laboratory) dose. The SAR RTL results in De estimates that are similar to OSL De estimates based on the UV emission.
UV-blue emissions from feldspars have often proved to be unacceptable dosimeters for age estimation given the intrinsic problem of anomalous fading. The potential of exploiting the far-red (> 665nm) IRSL emissions from potassium... more
UV-blue emissions from feldspars have often proved to be unacceptable dosimeters for age estimation given the intrinsic problem of anomalous fading. The potential of exploiting the far-red (> 665nm) IRSL emissions from potassium feldspars as a means of avoiding the ...
