پایش تغییرات مورفوتکتونیکی پادگانه‌های دریایی دریای عمان (چابهار تا گواتر)

در ایران پادگانه های دریایی (سواحل بالا آمده) یکی از مهم‌ترین عوارض ژئومورفولوژیکی در پهنه و خط ساحلی به شمار می‌آید. از 25 پادگانه دریایی در سواحل مکران (ایران و پاکستان) 12 پادگانه دریایی در ایران وجود دارند و تحت تاثیر فرایند های تکتونیکی ارتفاع یافته‌اند. در گذشته مطالعاتی در زمینه نرخ بالاآمدگی این پادگانه ها با استفاده از روش‌های تعیین سن مطلق انجام گرفته است ولی به واسطه محدود بودن تعداد آزمایش‌ها و هم چنین عدم امکان تعمیم نتایج به کل بخش‌های مختلف پادگانه ها، مطالعه یکپارچه این پادگانه ها در سطوح مختلف امکان پذیر نمی‌باشد. در این تحقیق سعی شده است تا با استفاده از تکنیک تداخل سنجی راداری و داده های envisat asar  و مدلsbas  پایش تغییر شکل پادگانه های دریایی چابهار، لیپار، بریس، پسابندر و گواتر در حد فاصل سال‌های 2003 تا 2011 انجام گیرد. نتایج به دست آمده نشان می‌دهد که تاثیر فعالیت‌های تکتونیکی بر روی پادگانه های دریایی تنها به صورت بالاآمدگی نیست و علاوه بر آن فرونشست های متعددی در پادگانه های به چشم می‌خورد. بیشترین نرخ میانگین بالاآمدگی مربوط به پادگانه دریایی لیپار با  میلی متر در سال (حداکثر 4.11 میلیمتر در سال) و بعد از آن چابهار با 0.34 میلی متر در سال و حداکثر (حداکثر 3.17 میلیمتر در سال) و پادگانه های گواتر و پسابندر در رتبه های بعدی قرار گرفته‌اند.

Monitoring morphotectonic evolution in the Oman Sea marine terraces (Chabahar to Quatre)

Extended abstractIntroductionMarine and lake terraces are one of the geomorphological features that exist in the coastal areas, which are due to the erosion of an old coastal platform, tectonic uplift of coastlines and fluctuations in sea level. The marine terraces may be located above or below sea level, depending on the time of formation. Due to the relatively smooth surface of the terraces, these terraces are commonly used for human activities. The study of sea and lake terraces is done for different purposes and by several methods, which include the use of radar interferometry to estimate marine terraces (rising coasts) which is one of the most important geomorphological features. Out of 25 marine terraces in the coast of Makran (Iran and Pakistan), there are 12 marine terraces in Iran and their elevation has risen under the influence of tectonic processes. In the past, studies on the rate of rise of these marine terraces have been done using the methods of determining the absolute age, but due to the limited number of tests and also the impossibility of generalizing the results to all different parts of the marine terrace, a comprehensive study of this marine terrace are not possible at different elevation levels. Therefore, the use of radar interferometry technique allows a more comprehensive study of this phenomenon.MethodsTo measure the deformation behavior of a phenomenon requires examining the time series of that phenomenon in the region. Therefore, several images must be available at different time intervals from that region and several interferometers must be inserted between different time intervals to calculate the rate of deformation in the calculations, which is known as interferometric time series analysis. For interferometric time series processing in this study, by selecting permanent scattering pixels in the whole region, the time series behavior of these pixels was investigated using the short base length (SBAS) method. In this research, ASAR radar sensor image of ENVISAT satellite obtained between 2003 and 2010 (Sarscape software) was used to implement each of the mentioned time series.Results and DiscussionThe results show that the impact of tectonic activity on marine terrace is not only uplift and in addition there are several subsidence in the terraces. The highest average rate of elevation is related to Lipar marine terrace with 0.73 mm per year (maximum 4.11 mm per year) and then Chabahar with 0.34 mm per year (maximum 3.17 mm per year). Guatre and Pasabandar terraces are in the next ranks.  ConclusionThe results of this study show the appropriate efficiency of ENVISATASAR satellite data and SBAS model in the study of deformation of Oman marine terrace. The highest rate of uplift in the study area is observed in Lipar and Chabahar, which has the effect of higher tectonic uplift and the highest altitude of Iranian marine terrace in this area. The uplift rate from the west of the region to the east is gradually decreasing, and this is accompanied by a decrease in the height of the marine terrace. Therefore, it can be assumed that the decrease in altitude of the terraces located in the west of Chabahar (Konarak, Gordim, Tang, Kalat and Jask) has been associated with a decrease in the uplift rate compared to Chabahar, which requires monitoring the altitude changes of the marine terrace in this area. The morphological effect of these uplifts in the study area can be seen in the formation of normal faults and the placement of the terraces in a flat manner and in their margins marl and sandstone precipices. This process has led to the emergence of sequences of sandstone and marl sediments on the surface and more severe erosion of marl sediments than sandstones has created a kind of differential erosion which is one of the morphological features of this coastal zone. Normand et al. (2019) has studied marine terrace on the coasts of Iran, using the method of carbon 14dating and with optical luminescence simulator index and the highest rate of elevation of sea terraces in this region during the period of 20 to 50 thousand years ago have been estimated to be 0.5 to 1.2 mm per year. The rate obtained in Normand studies is slightly higher than the rate obtained during the period studied in this study (20032009) and the slight difference between the displacement rates of these two studies can be related to its time dimension. The time period studied by Normand et al. (2019) is about 30,000 years ago and that during this time the uplift rate can be affected by variable tectonic activity and in some years this high rate is more than the transfer rate in the period studied in this research.