فهرست مطالب سمیه رستمی مهربان

While a crystalline material is heated from room temperature to around 500°C, a weak but measurable light will be emitted. This light is known as thermoluminescence (TL)‎ and is based on storage of energy from ionizing radiation in many naturally occurring TL minerals, including quartz and feldspar. The source of radiation is the radioactive materials such as uranium, thorium, potassium and cosmic radiation. The physical bases for this phenomenon in the simplest model can be expressed as follow: In nature all minerals are exposed to radiation, which leads to ionization of the atoms as electrons and holes. Freed electrons may become trapped in structural defects. The number of trapped electrons will be accumulated up to the time that the material is heated sufficiently. Heating stimulate the atoms and electrons can be released and recombine with the ‘holes’. Some of these holes are called 'the luminescence center's in the mineral crystal lattice which recombination of electron with them, results to an emission of light which is called thermoluminescence. When mineral is heated to high temperature, it loses all its previously acquired TL signal, and sets luminescence clock to zero. After cooling, the natural radioactivity causes thermoluminescence to build up again and thus the amount of TL induced is proportional to the time that has elapsed since the minerals were fired. For dating in laboratory, it is necessary to measure equivalent dose and dose rate. The intensity of the radiation damage in crystal lattices is a measure of the Equivalent Dose (DE)‎ which the mineral has received since last “resetting” by exposure to heat. DE is obtained by means of a TL measurement. The dose rate (DR)‎ is a measure of radiation dose per unit of time absorbed by mineral. The equation for obtaining an age is: Age (ka)‎ = DE (Gy)‎/DR (Gy/ka)‎ Two approaches are employed to determine the DE: the additive-dose method and the regeneration method. In this study, we used the first method. In additive-dose method, a number of nearly equal portions of the sample (aliquots)‎ are divided into groups; one is reserved for measurement of the natural TL signal only, while the others are given various doses of laboratory radiation. Then, all the aliquots are measured together and the luminescence intensity is plotted against laboratory radiation dose; this forms the sample’s dose response. The DE is determined from the intercept of the fitted line with the dose. The dose rate is calculated from an analysis of the radioactive elements in both the sample and its surroundings. These are determined using the measured concentrations of radioactive elements (uranium, thorium, potassium-40) within the sample and its surroundings, which are, in turn, converted into dose rates using standard conversion factors and formulae. Contribution of cosmic rays is also determinated. There are different methods for obtaining concentrations of radioactive elements such as γ-Spectrometer, ICP Mass Spectrometer, Notrun Activation, α counting and flame photometry. Thermoluminescence dating began in 1960- 1970, with age determination of pottery and other fired material in archeology and then it was employed in the other science such as paleoseismology, paleoclimatology, geology, archeology and geography. Iran is an ancient country which is located on the belt of earthquake, so most of ancient monuments and old civilizations have been destroyed by earthquake or other natural disasters. Dating can be a device to relate paleoseismology, paleoclimatology and archeology in Iran. Therefore, having knowledge of dating methods, especially luminescence, is so important for experts in geography, archeology, geology, seismology students and etc. In addition to an introduction to TL dating, this study has dated five potteries from Iran national museum in a range of 1000 to 4000 years.

Iran is one the most tectonically active parts of the world and regularly experiences earthquakes of both low and high magnitude. Therefore, earthquake hazard assessment before any kind of building construction and for already built and populated area is essential. A vital first step in this type of study is to identify, map, and determine the activity of faults within a given region. Investigating fault activity requires estimation of the average fault slip-rate, the recurrence interval between earthquakes, and the time of the last earthquake produced by each individual fault. Neyshabour is one of the most important cities in NE Iran. The city has been destroyed four times by major historical earthquakes. Three large faults exist in the region (the North Neyshabour, Binalud and Neyshabour faults). The North Neyshabour and Binalud faults lie at the foot of the Binalud range north of Neyshabour. The North Neyshabour fault has a relatively sinuous surface trace, typical of a thrust fault, and does not show any clear strike-slip component. The North Neyshabur thrust fault is exposed in a river section, at 36o180N 58o500E. The fault dips 60o north, and forms ~8-9 m high fault scarp at the surface which vertically offsets a Quaternary terrace. Within the river section, a yellow sandstone unit is offset by 9 m. A 60 by 40 cm sample of this unit was collected from the river exposure for optically stimulated luminescence (OSL) dating (location: 36o18.3090N 58o50.2700E). The sample was dated in the Oxford luminescence lab using a Riso (Model TL/OSL-DA-15) automated TL/OSL system under subdued red light (for details of the method see Fattahi et al., 2006, 2007; Fattahi and Walker, 2007). Eighteen subsamples of sample N5 demonstrated a wide paleodose distribution. This suggests that the sediment may not have been completely reset upon deposition (i.e. not all ‘trapped’ electrons from an earlier burial period were reset during sediment transport). This causes the mean age determination using weighted mean, 42000-68000 year, to overestimate the real deposition age. One solution to this problem is to assume the date of the youngest grains represent the time of deposition, giving a lower age of 22200-26000 year. However, we decided to use both age estimates for slip rate determination. As the top Quaternary terrace, has been displaced ~ 8-9 m at the surface, we calculated two slip rate using both average and minimum ages for calculating the slip-rate on the North Neyshabur fault (~0.1–0.2 and ~0.3-0.4mm/yr), respectively.

Neyshabour (approximately 200,000 pop.) lies on the southern margin of the Binalud mountains in NE Iran. The city has been destroyed four times by major historical earthquakes (in 1209, 1270, 1389 and 1405 A.D.).Three large faults occur in the region. The Binalud and North Neyshabur faults lie at the foot of the Binalud range north of Neyshabour. The Neyshabour fault lies within the valley west of Neyshabour. The Neyshabour fault, which lies 10 km south of the North Neyshabur fault, is 50 km long thrust. At each end of the Neyshabour fault two young, 10 km-long, thrust segments occur. It is close to Neyshabour city; and is a probable source of the 1209 and 1405 earthquakes. It poses a substantial seismic risk to the city because of the potential for future activity. Slip rate is one of the important parameters for seismic hazard assessment which was determined using SRTM for offset measurement and OSL for age calculation. Luminescence was measured through 7 mm Hoya U-340 filters in a Risø (Model TL/OSL-DA-15) automated TL/OSL system. The equivalent dose (De) was obtained using the conventional quartz single aliquot regeneration method (Murray and Wintle, 2000). Twelve aliquots have been processed for the sample, of which only the aliquots were accepted that satisfied the SAR restrictions. De was estimated using analyst program. Age was calculated using a weighted mean De for the sample. The Dose rate was obtained using uranium, thorium and potassium concentrations, which were measured by Micro Nomand portable gamma spectrometer in field. The results are presented in Table 1. Dividing the displacement by the minimum and the maximum ages provided the slip rate to be 0.1-0.2mm/yr.