عنوان مقاله
کاربرد رادار نفوذی به زمین برای عکس برداری از درزه های ورقه ای در سنگ بستر گرانیتی
بخشی از مقاله
منطقه حیدر اباد شمال غرب داروارکراتون شرقی را پوشانده است که عمدتا متشکل از گرانیت ها و گنیس های 2.5 تا 2.7 میلیون ساله با رگه های نازکی از کمربند های شیست رسوبی و اتشفشانی می باشد. از نظر ساختار مورفولیژیکی این منطقه متشکل از توده های گرانیتی شبه دایره ای است که تقریبا توسط رودخانه کاریشنا و مانجرا به ترتیب در شمال و جنوب محصور شده است. همچنین در این منطقه گرانیت های دانه درشت و گرانیت های با بافت پورفیری همراه با امفیبیولیت و گنیس های میگماتیت در منطقه می باشد. آرایشات ساختاری و تشکیلات سازه ای در حیدر اباد و اطاف ان زیاد هستند. این آرایشات یا گسل های خطی شامل دره های ژئومورفیک سیستم زهکشی رودخانه ای و ارتفاعات توپوگرافی خطی طویل با جهت های اصلی N–S, NE–SW و ESE-WNW شناخته می شود.
کلمات کلیدی:
Ground-penetrating radar applied to imaging sheet joints in granite bedrock Granitic rocks commonly develop exfoliation surfaces (also called as sheet joints), which are generally surfaceparallel fracture systems. These structures may form in response to: (i) exhumation processes in which erosion causes upliftment of buried rocks; (ii) physical weathering due to thermal expansion and contraction; (iii) groundwater-related chemical weathering, and (iv) tectonic deformation. Although these structures are interesting geological features giving insights into past geological processes1,2, they have several other implications for engineering geological applications and groundwater exploration. The exfoliation joints can transport large volumes of groundwater laterally for long distances in many directions. Geological mapping of these structures is possible only on cliff sections, whereas in the near surface they cannot be detected. Geophysical studies can greatly help in locating them in the subsurface. In this communication, we demonstrate the application of ground-penetrating radar (GPR) in detecting subsurface exfoliation joints in granite exposure area near Durgam Cheruvu, a micro-earthquake zone in Hyderabad (Figure 1). The findings would be helpful for planning underground excavation (e.g. construction of tunnels), modelling groundwater flow systems, and designing foundation structures of large-scale building structures. Hyderabad area forms the northeastern extension of the Eastern Dharwar Craton, which is largely composed of ~2.7– 2.5 Ga-old granites and gneisses with minor narrow tracts of meta-volcanicsedimentary schist belts3,4. Morphostructurally, this area is composed of nearcircular granite massifs, which are approximately bounded by the Krishna and Manjeera rivers in the north and south respectively. It largely exposes Archaean medium to coarse-grained granites, porphyritic granites with small inclusions of amphibolites and migmatitic gneisses at places. Structural lineaments are abundant in and around Hyderabad. These lineaments are geomorphic valleys, river drainage systems and long-linear topographic highs on ground, with major orientations of N–S, NE–SW and ESE– WNW5 . The study area is near Durgam Cheruvu that experienced micro-earthquake events in 1994, 1995 and 1998 (refs 6 and 7).
