Informatics Publishing Limited

Malay Mukul ¹, Sridevi Jade ², Kutubuddin Ansari ¹, Abdul Matin ³

Affiliations
1 Department of Earth Sciences, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, IN
2 CSIR-4PI, Formerly CSIR-CMMACS, Wind Tunnel Road, Bangalore 560 037, IN
3 Department of Geology, University of Calcutta, 35 Ballygunge Circular Road, Kolkata 700 019, IN

Abstract

The Darjiling-Sikkim Himalaya (DSH) is located over the Dharan-Gorubathan salient-recess pair and moderate thrust and strike-slip earthquake occur here. The hypocentres cluster not only near the location of the Main Himalayan Thrust (MHT) or the basal decollement of the Himalayan wedge, but also well above and below it. The epicentres cluster over the mapped location of the Lesser Himalayan Duplex (LHD), suggesting that both MHT and LHD are active structures in DSH. The earthquakes below MHT can be related to transverse strike-slip faulting in DSH associated with salient-recess transition on both flanks of the Dharan salient. The 18 September 2011 (Mw 6.9) strike-slip event suggests that the western flank of the Dharan salient is also likely to contain an active transverse strike-slip fault like the Gish Transverse Fault (GTF) on its eastern flank. High-precision Global Positioning System measurements (1997-2006) indicate that a maximum of ∼4 mm/year convergence is being accommodated in the Tista Half-Window or LHD west of the surface trace of GTF and DSH is locked south of 27°N both east and west of GTF about 10 km north of the Himalayan mountain front. About 3-4 mm/year sinistral strike-slip is postulated on GTF north of 27°N. Dislocation based forward modelling using two thrust dislocations with oblique slip and a sinistral strike-slip dislocation generated velocities that were closest to the measured back-slip velocity field in DSH.

Keywords

Darjiling–Sikkim Himalaya, Dislocation Modelling, Global Positioning System, Gish Transverse Fault, Recess, Salient, Seismicity.

Full Text

   

Malay Mukul ¹, Sridevi Jade ¹, Anjan Kumar Bhattacharyya ², Kuntala Bhusan ³

Affiliations
1 CSIR Centre for Mathematical Modelling and Computer Simulation, Bangalore - 560 037, IN
2 Department of Physics, Tezpur University, Tezpur - 784 028, IN
3 North East Space Application Centre, Umiam - 793 103, Meghalaya, IN

Abstract

Deformation in active mountain belts like the Himalaya is manifested over several spatial and temporal scales and collation of information across these scales is crucial to an integrated understanding of the overall deformation process in mountain belts. Computation and integration of geological shortening rates from retrodeformable balanced cross-sections and present-day convergent rates from deforming mountain belts is one way of integrating information across time-scales. The results from GPS measurements carried out in NE India indicate that about 15-20 mm/yr of convergence is being accommodated there. Balanced-cross sections from the NE Himalaya indicate about 350-500 km of shortening south of the South Tibet Detachment (STD). Geothermobarometry suggest that the rocks south of the STD deformed under peak metamorphic conditions at ~ 22 Ma. This indicates a geological convergence rate of ∼ 16-22 mm/ yr which appears to be fairly consistent with the GPS derived convergence rates. Approximately 1.5 to 3.5 mm/yr (∼ 10- 20 %) of the total N-S of the present-day convergence in the NE Himalaya is accommodated in the Shillong Plateau. In addition, ∼ 8-9 mm/yr of E-W convergence is observed in the eastern and central parts of the Shillong Plateau relative to the Indo-Burman fold-thrust belt. Balanced cross-sections in the Indo-Burman wedge together with higher resolution GPS measurements are required in the future to build on the first-order results presented here.

Keywords

GPS Geodesy, North East Himalaya, Geological Shortening, Convergence, Active Tectonics.

Full Text

     

Chiranjeevi G. Vivek ¹, T. S. Shrungeshwara ¹, Sridevi Jade ²

Affiliations
1 CSIR-Fourth Paradigm Institute (CSIR-4PI), Wind Tunnel Road, Bengaluru 560 037,, IN
2 Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201 002, IN

Abstract

This study evaluates the impact of multi-GNSS (Glob-al Navigation Satellite System) signals on the estima-tion of precise position with millimetre accuracy. Compared to standalone satellite systems like the Global Positioning System (GPS), multi-GNSS im-proves start-up time, performance, satellite visibility, accuracy, spatial geometry and reliability. However, on the flip side it increases the noise, signal inter-ference, hardware complexity of the receiver, inter-system interference and computation complexity which may degrade its performance. Though GNSS is similar at fundamental levels, differences exist in sig-nal structures, reference frames and timing standards. Compatibility and interoperability between the differ-ent constellations of the highest order is required to achieve the best results. At present, GPS and Glonass navigation systems are fully functional with global coverage and comparable precision. Glonass satellite constellation, signal structure is slightly different when compared to GPS, whereas major differences exist in the reference frame and epoch time. Com-bined GPS–Glonass solution significantly improves the accuracy in navigation applications with increased satellite signal observations and spatial distribution of visible satellites. For precise geodetic studies using static post-processing, combined solution may degrade the accuracy, if these differences are not handled care-fully. Currently for geodetic studies, only GPS obser-vations are majorly used worldwide. For the first time, daily precise position is estimated for continuous GNSS stations located in India using static post-processing with standalone GPS, Glonass as well as combined GPS–Glonass to study the impact of multi-GNSS signals for geodetic studies.

Keywords

Glonass, GNSS Signals, GPS, Multi-GNSS Data Analysis, Position.

Full Text