ارزیابی زمین‌ساخت فعال نسبی در حوضه آبخیز آبشینه همدان با استفاده از شاخصه‌های زمین‌ریختی و لرزه‌خیزی منطقه‌ای

نویسندگان

چکیده

شاخص­های زمین­ریختی به دلیل ارتباطی که با میزان و نوع فعالیت‌های زمین‌ساختی دارند می­توانند به‌عنوان معیاری کارآمد برای تشخیص زمین‌ساخت فعال مناطق وسیع به کار روند. مطالعات در مناطق مختلف جهان بر کارایی این شاخص‌ها تأکید کرده‌اند. در پژوهش حاضر با استفاده از شاخص‌های زمین­ریختی عدم تقارن حوضه زهکشی، نسبت پهنای کف دره به ارتفاع دره، شکل حوضه، تقارن توپوگرافی عرضی، منحنی هیپسومتری حوضه، پیچ‌وخم رود و شیب طولی رودخانه آبشینه در حوضه آبخیز آبشینه برای تحلیل فعالیت زمین­ساختی این حوضه استفاده‌شده است. برای مقایسه، ابتدا با جمع­آوری داده‌های زمین­لرزه­های تاریخی و دستگاهی نسبت به ارزیابی فعالیت لرزه­ای منطقه اقدام شد. سپس لرزه­خیزی منطقه به روش تحلیل خطر لرزه­ای تعینی (DSHA) با استفاده از ویژگی‌های گسل‌های موجود برآورد گردید. نتایج نشان می­دهد که در اغلب شاخص‌ها نشانه‌های فعالیت حوضه آبخیز آبشینه بارز است. بررسی پیشینه لرزه­خیزی منطقه، بر فعالیت زمین­ساختی منطقه موردمطالعه تأکید دارد. روش تحلیل خطر لرزه­ای تعینی نیز با به دست دادن مقدار بزرگی بیشینه 8/6 ریشتر و بیشینه شتاب افقی g4/0 نسبت به مرکز ثقل حوضه، منطقه موردمطالعه را ازنظر لرزه‌خیزی فعال نشان می‌دهد.

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عنوان مقاله [English]

Evaluation of relative active tectonic in Abshineh basin of Hamedan, by using of geomorphic indices and regional seismicity

چکیده [English]

Introduction
In the past decade, there has been a huge progress in development of quantitative geomorphology especially in terms of statistical tools and mathematical models. Vast research carried out in this field resulted in the useful quantity Geomorphological methods describing the morpho-evolotive processes and, also, in studying the active tectonic regions.
The neotectonic effects on morphogenetic processes have been determined through the application of statistical analysis. The study of tectonic activity, and in particular those areas with relatively high activity, in the Holocene and late Pleistocene is important to evaluate the earthquake hazard. Geomorphic indices due to relationship with rate and type of tectonic activity can be used as efficient criterion for recognize the tectonic activity in vast regions. These indices are useful for recognize the fast tectonical deformations. From this information used to obtain the detail active tectonic in special region. Each indices presents a relative classification of tectonical activity. When several indices are used for a region rather than used only one index gives meaningful results. A comparison of several morphometric indices of geomorphological features, especially with tools such as geographic information systems (GIS), can provide a valuable quantitative method. This procedure presents relative rates of tectonic activity. Studies in different regions in the world such as Azañón et al (2012), Bagha et al (2014), Hamdouni et al (2008), Alipoor et al (2011), Ildoromi (2011), Ezati & Agh-Atabai (2014) and etc, have been emphasized on workability of these indices.
Methodology
Abshineh basin with 22155 Hec area located at SE of Hamedan city at 48°28 ʹ 14″ to 48° 48 ʹ 3″ E longitude and″ َ34°34 ʹ 56″ to 34°45 ʹ 5″ N latitude in central Zagros. Maximum elevation of this basin is 3580 m from sea level. The annual temperature average of this region is +12.23˚c. The coldest month is February and the hottest is August. The annual average precipitation of this region is 313 mm. According to Ambrothermic curve, the driest months are May to September. The regional climate according to Ambreget method is semi-arid cold and semi-humid.
The indices represent a quantitative approach to differential geomorphic analysis related to erosion and depositional processes that include the river channel, long profile, and valley morphology as well as tectonically derived features, such as fault scarps. Indices of active tectonics may detect anomalies in the fluvial system or along mountain fronts. These anomalies may be produced by local changes from tectonic activity resulting from uplift or subsidence. The main objective of the study was fulfilled by computing the geomorphic indices by using remote sensing and GIS techniques. The study used ASTER and Landsat data and GIS interpretive techniques to analyze and calculate these indices.
In this study, Drainage Basin Asymmetry Factor, Ratio of Valley- Floor with to Valley Height, Basin Shape Factor, Transverse Topographic Symmetric, Hypsometric Integral, River Sinuosity Index, Stream Length- Gradient Index of Yalfanrod river in Abshineh basin for analysis the tectonic activity of this basin were used. For evaluation of active tectonic by geomorphic indices first obtained these indices of Abshineh basin then compared with active tectonic classifications such as Bull and McFadden, (1977), Rockweel et al. (1985), Silva et al. (2003) and El Hamdouni et al. (2008).
For comparison, first by gathering the data of historical and instrumental earthquakes of study area, the seismic activity of the region was assessed. Then, by using the characteristics of faults, the seismicity of the region was determined by Deterministic Seismic Hazard Analysis (DSHA) method.
Results and discussion
Morphotectonic analysis by the use of geomorphic indices serves as a tool of recognition in regions with active tectonic deformation. Landforms in active deformation area are created from interaction of tectonic and surfacial processes. One of the most important landforms in ground is rivers that are very sensitive to tectonic movements especially uplift and tilting. Thus based on analysis of the rivers and related drainage networks by the use of geomorphic indices one is able to attain valuable information about tectonic history of the area.
The results of this study show that in the most of indices, activity of the Abshineh basin was manifested. The results of geomorphologic indices analyze show that this basin in some indices such as Drainage Basin Asymmetry Factor, Transverse Topographic Symmetric, River Sinuosity Index, Stream Length- Gradient Index is active and in Ratio of Valley- Floor with to Valley Height, Basin Shape Factor and Hypsometric Integral is semiactive.
Investigation of the region background seismicity underscores on tectonic activity of the study area. Also, the results of deterministic seismic hazard analysis method (6.8 Richter magnitude and 0.4g peak ground acceleration) show the region active seismicity.
Conclusion
Comparing of results of geomorphologic indices analyzes, region seismicity evaluation and Deterministic Seismic Hazard Analysis (DSHA) addition to basin active tectonic confirm the performance of geomorphologic indices for distinguish the basin tectonical activity. It seems that these results can be used in some human activity such as improving construction sites for watershed management.

کلیدواژه‌ها [English]

  • Active Tectonic
  • Geomorphologic indices
  • Deterministic Seismic Hazard Analysis (DSHA)
  • Abshineh basin