Abstract:
در بیشتر مواقع برای شناسایی گسلهای پنهان از روشهای ژئوفیزیکی استفاده کردهاند. در پژوهش حاضر قابلیت ژئومورفولوژی جهت شناسایی گسلهای پنهان مورد بررسی قرار گرفت. ازجمله مناطقی که رسوبات رودخانهای آثار گسلها را مدفون ساخته است شرق استان کرمانشاه است. با بررسی ژئومورفولوژی منطقه و براساس فرضیه جدایی طاقدیس شیرز از سفره رورانده و دیگر شواهد مورفوتکتونیکی حدود کلی گسلهای پنهان شناسایی و بر روی نقشه زمین شناسی ترسیم شد. در مرحله بعد با پردازش دادههای مغناطیس هوایی، موقعیت دقیقتر گسلها ترسیم شد. سپس بر روی 4گسل، 5 مقطع برداشت VLF و مغناطیس زمینی صورت گرفت و نتایج مربوط به مراحل پیشین با استفاده از روشهای ژئوفیزیکی نیز صحت سنجی شد. اولین گسل از غرب ارتفاعات پرآو و از شمال دشت کرمانشاه به سمت شرق بر روی ارتفاعات پرآو و بیستون امتداد مییابد و با گذشتن از ارتفاعات برناج به سمت غرب وارد دشت شده و پس از عبور از دشت صحنه مجددا با تغییر روند به سمت شمال شرق امتداد مییابد. در فاصله بین ارتفاعات بیستون تا دشت صحنه 5 گسل با جهت شمال- جنوب و منشعب از گسل اول تا حدود طاقدیس شیرز امتداد دارند. گسل دیگر از غرب شهر کرمانشاه آغاز شده و در جنوب ارتفاعات پرآو با تغییر مسیر به سمت جنوب شرق ادامه مییابد و وارد دشت هرسین می-شود. مقایسه نتایج ژئومورفولوژی، ژئوفیزیک و مغناطیس هوایی نشان میدهد که ژئومورفولوژی قادر است گسلهای بزرگ و پیسنگی عمیق آشکار و حتی پنهان، که اثرات خود را در مورفولوژی منطقه برجای گذاشتهاند، را شناسایی کند.
Introduction In most cases, faults can be detected by signs; however, in many cases, the outcrops of these structures have not reached the surface of the earth, or deposits have been buried with evidence and indications. Such conditions, although the surface of the earth's crust on both sides of the fault is displaced and drifting up or down, however, the surface out crop of the fault is not observed at the ground or is limited to stacks and mild folds in sections along the fault. To identify these types of faults, geophysical methods, CO2 and soil radon measurements, seismic reflections and electrical imaging, lidar, penetrating ground radar or air geophysics can be used. Researchers who have studied the buried faults of the earth's crust have generally used geophysical methods. According to Giving and colleagues, the results of aerial geophysical data in order to identify hidden faults, if accompanied with evidence of geomorphology and topographic data, have higher scientific value. In this research, the aim is to find hidden faults through geomorphic interpretation methods. Methodology Among the areas where active tectonics and faults have been buried and the river sediments have buried their works, the east of Kermanshah province is in the Harsin and Bisetoon plain. First, geological maps and topography, geomorphology, and geostructral were explored and interpreted. Based on the hypothesis of the separation of the Shirez anticlinal from the nape as one of the geostructural and morphotectonic evidence, and the flow of the Gamasyaw river and the morphology of the Tsetonic plain of Harsin, the overall boundary of the hidden faults was identified and mapped to geology. In the next step, by studying the data of aeromagnetism and the use of return-to-pole filters, vertical derivatives, analytical signal and tilt, a more precise location of the faults was maped. Then, on the 4 main faults identified, 5 sections of VLF As and Mg As were taken and the results of the previous steps were verified using the geoelectric method. Results and discussion What is obtained from the results of a total of three methods used to identify hidden faults is a number of faults that have been scattered across the region. The first fault in the almost west to east direction from west of the Taqbostan elevations in the north of Kermanshah plain extends over the Taqbostan elevations, and after passing on the Prao and Bisetoon elevations, with the shift of direction from southwest to northeast to Barnaj, and from there with change the almost east-easterly direction enters the plain and continues in the south of the Khaneh-khode mountain, and after passing through the Sahneh plain, it again extends to the north-east by changing the trend. Between the Bisetoon elevations to the Sahneh plain, 5 faults along the north-south direction extend approximately from the first fault to the shores of the Shirez anticlinal. These faults have been driven by the sliding motion. Another fault that seems to play an important role in the region's morphology and history of geomorphology in the region has started from west of Kermanshah and in the south of the Paro elevations it continues along the southeast to the Harsin plain. Comparison of the results of the three stages of the research showed that what the aeromagnetism and geoelectrics identified as faults, geomorphology, with a small spatial variation, and a negligible distance, as a fault that must exist to justify the region's morphology had identified. Geomorphology is largely capable of treating anomalies and movements caused by faults that are sometimes detected in the field by interpreting geospatial maps and analyzing the geostructural of the area along with simultaneous surveys of geomorphic, topographic, satellite images and remote sensing maps that geologists can not be identified. What is certain is that the effect of hidden faults in the region's morphology is observed only in some areas where the effect of the fault has reached the surface directly and in the expected form; otherwise, in the identification and tracing of the hidden fault by geomorphology, we must look for indirect effects and the effects of long-term faults on morphology, especially geostructural, on a larger scale than the usual methods of morphotectonic studies. It can be said that geomorphology can be successful in finding hidden faults that it has a comprehensive view on geotechnical and past geographic of region. In fact, a thorough examination of the geomorphological nature of the forms is based on the interpretation of the function of the faults, in particular the hidden faults, which themselves sometimes lead to the finding of hidden faults.
Machine summary:
با بررسي ژئومورفولوژي منطقه و براساس فرضيه جدايي طاقديس شيرز از سفره رورانده و ديگر شواهد مورفوتکتونيکي حدود کلي گسل هاي پنهان شناسايي و بر روي نقشه زمين شناسي ترسيم شد.
نتايج پژوهش آنان نشان داد که روش ژئوالکتريک با توجه به تنوع در آرايش ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ 1 Kumar 2 Zhu 3 Bonforte 4 Carvalho 5 Saetanga 6 LIDAR 7 Guiang 8 Rajaram 9 Greendale و ارزاني آن ميتواند مورد توجه ويژه قرار گيرد و نقش مهمي در تعيين مشخصات گسل هاي پنهان مخصوصا تعيين امتداد گسل هاي پنهان در مناطق مسکوني که امکان انجام اندازه گيريهاي ژئوفيزيکي وجود ندارد، ايفا نمايد.
(به تصویر صفحه مراجعه شود) شکل شماره ١: موقعيت و نقشه زمين ساخت منطقه مورد مطالعه داده و روش تحقيق به طور کلي پژوهش حاضر طي سه مرحله انجام گرفت : بررسي شواهد ژئومورفولوژي و زمين ساخت گسل هاي پنهان ، پردازش داده هاي مغناطيس هوايي جهت يافتن گسل هاي پنهان و مقايسه با گسل هاي شناخته شده توسط مورفوتکتونيک ، صحت سنجي نتايج مربوط به مراحل قبل توسط روش هاي ژئوفيزيکي VLF و مغناطيس زميني .
تفسير بصري نقشه هاي زمين شناسي و ژئومورفولوژي منطقه احتمال وجود گسل هايي در جهت عمود بر گسل اصلي زاگرس ، که موجب حرکت طاقديس شيرز در امتداد ١٥ کيلومتر به سمت جنوب شده است را نشان ميدهد.