Geodynamics Research International Bulletin

8

Authors: Tejpal Singh, A.K. Awasthi, Ravindra Kumar, N.S. Virdi

Direct evidences of faulting along the Himalayan mountain front are very rare. The most conspicuous indicators of the presence of a structural discontinuity and an active tectonic boundary are manifested in the geomorphology. In most cases, a topographic break defines the outermost Himalayan thrust fault i.e. Himalayan Frontal Thrust (HFT). However, the nature of this tectono-geomorohic boundary tends to vary significantly along the strike of the mountain belt. In some sectors, it is marked by the presence of elongated intermontane valleys popularly known as ‘duns’, whereas other sectors are conspicuous by their absence. The Nahan sector of the Western Indian Himalaya is one such area that is characterized by the absence of intermontane valley. Here, in this article we emphasize that the absence of intermontane valleys in the Nahan sector gives rise to a distinctive geomorphic expression of the active tectonic boundary. In the Nahan sector, active slip along the underlying thrust faults and splays has resulted in the accumulation of high relief spread over a relatively smaller area. This led to the absence of the duns in this area. Also, the topographic boundary closely corresponds to a number of drainage anomalies establishing the active tectonic nature of the HFT. The drainage anomalies mainly include the deflection of streams, widening of channels and increase in their sinuosity as they approach the mountain front. The increase in the sinuosity of the channels is also marked by degradation activity and presence of broad flat terrace surface that confirm to the tectonic uplift in this area.

9

Authors: Farzad Shirzaditabar, Somaye Shahab

An inversion method based on Occam's inversion algorithm was developed to recover the resistivity and thickness of a layered ground. Synthetic data was obtained via Res1Dinv software and values of noise were added to them. Then, 1D forward and inverse algorithms were used to recover the main model from noisy data. Applying the Occam’s inversion to synthetic data created over some 1D model with multiple sequences of resistive and conductive layers. The results showed that this method works well and the predicted models can be good approximations of synthetic models. On the other hand, the intrinsic limitations of DC resistivity method, e.g. the principle of equivalence, cannot be resolved. Besides, the Occam's inversion procedure cannot estimate the depth of real interface of adjacent layers.

9

Authors: Roya Khaleghi, Seyed Reza Mehrnia

This research is based on the interpretations seismic, gravity and magnetic data it has been proceed on perusal of hidden faults in the north Qazvin area with radius 40 km of Qazvin city center. Contour maps processed by using of Geosoft, Surfer and Matlab specialized software and magnetic and gravity lineaments have been prepared by using filter of first vertical derivative. This study shown that locus of magnetic and gravity lineaments are consistent together with geological surface structure. Research method is based on a local analysis to the 56432 points interpolation in isometric grids. Also, we have discussed in facies changes and it’s relation with linear process of gravity gradients by geological map of region and interpolation tectonic considerations (observed faults by Berberian and gravity lineaments related to seismic events). Accessing to such a model, prepare to analysis of mechanisms of seismic attributed to north Qazvin fault (NQF) and it is prepared basis of new research for exploration model of hidden seismic faults which is provable their identity in terms of geophysical.

11

Authors: Mehdi Eshagh, Mohammad Bagherbandi

In this study, we developed three estimators to optimally combine seismic and gravimetric models of Moho surface. The first estimator combines them by their special harmonic coefficients; the second one uses the spherical harmonic coefficients of the seismic model and use integral formula for the gravimetric one. The kernel of the integral terms of this estimator shows that a cap size of 20◦ is required for the integration, but since this integral is presented to combine the low frequencies of the gravimetric model, a low resolution model is enough for the integration. The third estimator uses the gravity anomaly and converts its low frequencies to those of the gravimetric Moho model, meanwhile combining them with those of seismic one. This integral requires an integration domain of 30◦ for the gravity anomalies but since the maximum degree of this kernel is limited to a specific degree, the use of its spectral form is recommended. The kernel of the integral involving the gravity anomalies, developed for recovering high frequencies of Moho, is written in a closed-from formula and its singularity is investigated. This kernel is well-behaving and decreases fast, meaning that it is suitable for recovering the high frequencies of the Moho surface

13

Authors: Zhensheng Wang, Timothy M. Kusky, Xianmin Wang, Hui Li, Jie Lin

An algorithm for removing unreasonable closed depressions from raster Digital Elevation Models (DEM’s) is proposed. This algorithm is based on the basic feature points (entrance, nadir and outlet) of topographic depressions and a directional erosion mechanism. The main process is a pixel-by-pixel elevation-reducing method that allows water to flow and erode obstacles iteratively from a depression entrance to a depression nadir, and then to a depression outlet. Therefore, unreasonable closed depressions can be removed from DEM’s without the need of any other auxiliary information. We applied the method to some real areas in the Yangtze and Yellow River watersheds and the results demonstrate that our approach can keep more original DEM information in depression areas than the traditional filling idea, thus it provides a better method to extract more accurate drainage lines in topographic depressions.

16

Authors: Arash Bakhshi Pour Sedaposhte, Saeed Javaherzade

In the underground tunnels after the excavation and temporary support system, the most important factor in the behavior survey of the ground and temporary supporting system (Including Ltys and shotcrete) is to use instruments that have been used in the study of Convergence Meter. The results of monitoring are useful to make sure of the accuracy of the numbers presented. In this paper, all factors affecting Qom underground tunnel monitoring and the modified results were investigated. The effect of each error and factors affecting the monitoring results were extracted as numbers. Among the factors affecting the monitoring results are import correction factors, (Calibration and temperature) machinery operation while reading, Cement slurry injection into falling sites, tunnel excavation method (TOP and BENCH), Convergence pin installation method (before or after shotcrete), Kafband Installation, repairs and meter cutting, one or two push working with the afore-mentioned machine. The purpose of this paper was to enhance the precision of the instrument that we expected from convergence meter with regard to the influential factors. Considering the listed problems and their solutions presented in this paper, best results are obtained by the analysis of the instrument.