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Assessment of the Relative Largest Earthquake Hazard Level in the NW Himalaya and its Adjacent Region

Tsapanos T. M., Yadav R. B. S., Olasoglou E. M., Singh M.

Acta Geophysica

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2016

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Vol. 64, no. 2

362--378

EN

In the present study, the level of the largest earthquake hazard is assessed in 28 seismic zones of the NW Himalaya and its vicinity, which is a highly seismically active region of the world. Gumbel’s third asymptotic distribution (hereafter as GIII) is adopted for the evaluation of the largest earthquake magnitudes in these seismic zones. Instead of taking in account any type of Mmax, in the present study we consider the ω value which is the largest earthquake magnitude that a region can experience according to the GIII statistics. A function of the form Θ(ω, RP6.0) is providing in this way a relatively largest earthquake hazard scale defined by the letter K (K index). The return periods for the ω values (earthquake magnitudes) 6 or larger (RP6.0) are also calculated. According to this index, the investigated seismic zones are classified into five groups and it is shown that seismic zones 3 (Quetta of Pakistan), 11 (Hindukush), 15 (northern Pamirs), and 23 (Kangra, Himachal Pradesh of India) correspond to a “very high” K index which is 6.

2

Crustal thickness and poisson’s ratio variations across the northwest Himalaya and eastern Ladakh

Hazarika D., Kumar N., Yadav D.

Acta Geophysica

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2013

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Vol. 61, no. 4

905--922

EN

Crustal thickness and PoissonPoisson's ratios are estimated across the northwest (NW) Himalaya and eastern Ladakh applying H-k stacking method on receiver functions of teleseismic earthquakes recorded at 16 broadband seismological stations. The results show significant lateral variation of crustal thickness from the Lesser and Higher Himalaya (~50 km thick) to Ladakh (~80 km thick) through the Indus Tsangpo Suture Zone (ITSZ). The Indian Moho is continuously traceable across the ITSZ which is consistent with the underthrusting of the Indian plate beyond the surface collision boundary. The estimated Poisson's ratio is intermediate in the Tethyan Himalaya (0.269-0.273) and high beneath Ladakh (0.280-0.303), indicating the effect of aqueous fluid/partial melt present in the crust.

3

Estimation of crustal Qβ in the NW Himalaya using teleseismic broadband SH waveforms of the 8 October 2005 South Asian earthquake

Kumar S.

Acta Geophysica

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2010

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Vol. 58, no. 4

645-660

EN

The average value of the intrinsic shear wave quality factor, Qβ, for the 15 km of the upper crust in the NW Himalaya is estimated. Thirty-two teleseismic broadband SH and sSH waveforms of 8 October 2005 South Asian earthquake (Mw = 7.6), from sixteen Global Seismographic Network stations of the National Earthquake Information Center network have been used. The selected windows of the direct and depth phases have been Fourier transformed and smoothed using the Hamming and Tuckey technique. Ratio of the smoothed spectra of depth and direct phases are obtained in the frequency range 0.2-1.5 Hz. A straight line is fitted in the least-square sense to the spectral ratio versus frequency. The value of Q ß is estimated from the slope of the line. The frequency independent average value of Q ß is estimated to be 218±56.

4

Feasibility of the SAR technique on quartz sand of terraces of NW Himalaya: a case study from Devprayag

Jaiswal M. K., Srivastava P., Tripathi J. K.

Geochronometria

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2008

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Vol. 31

45-52

EN

Optically Stimulated Luminescence (OSL) dating technique based on the Single Aliquot Regenerative dose (SAR) protocol is being used increasingly as a means of establishing sediment burial age in the late Quaternary studies. Thermal transfer, low and changing luminescence sensitivity of quartz grains of young sedimentary belts of the New Zealand Alps and the north-east Himalaya poses problems in using SAR protocol. Records of active tectonics and signatures of palaeo-climate are preserved in the Quaternary – Holocene terrace sediments. Therefore, to unfold the history of successive tectonic and palaeo-climate events, robust chronological technique is needed. Palaeoflood deposits in NW Lesser Himalayan region receive quartz from the weathering of various rock types such as quartzite and phyllite in the Alaknanda Basin. A series of tests e.g. dose recovery, preheat plateau, thermal recuperation and change in sensitivity, were performed to check the suitability of quartz grains collected from the terrace sediment of Devprayag of the NW Himalaya, for OSL studies. Inferences were drawn regarding the source of the quartz grains on the basis of the geochemistry and luminescence intensity of the terrace sediment. The study shows that though quartz from the North West Himalaya are low in luminescence intensity but the reproducibility of De value makes the quartz sand suitable for SAR dating technique. Relation between luminescence intensity with CIA values help to predict the provenance of quartz sand. Tests show that the quartz from NW Himalaya is suitable for SAR protocol in OSL.