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Kayal, J. R.
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Kayal, J. R.
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- PublicationRestrictedThe attenuation mechanism of S-waves in the source zone of the 1999 Chamoli earthquake(2014)
; ; ; ; ; ;Mukhopadhyay, S.; Department of Earth Sciences, IIT Roorkee, Roorkee 247667, India ;Kumar, A.; Department of Earth Sciences, IIT Roorkee, Roorkee 247667, India ;Garg, A.; Department of Earth Sciences, IIT Roorkee, Roorkee 247667, India ;Del Pezzo, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Kayal, J. R.; School of Oceanographic Studies, Jadavpur University, Kolkata 700016, India; ; ; ; In the present study the attenuation mechanism of seismic wave energy in and around the source area of the Chamoli earthquake of 29th March 1999 is estimated using the aftershock data. Most of the analyzed events are from the vicinity of the Main Central Thrust (MCT), which is a well-defined tectonic discontinuity in the Himalayas. Separation of intrinsic (Q 1 i ) and scattering (Q 1 s ) attenuation coefficient is done over the frequencies 1, 2, 4, 8 and 16 Hz using Multiple Lapse Time Window Analysis (MLTWA) method. It is observed that S-waves and their coda are primarily attenuated due to scattering attenuation and seismic albedo is very high at all the frequencies. A comparison of attenuation characteristics obtained using these aftershock data with those obtained using data of general seismicity of this region reveal that at lower frequencies both intrinsic and scattering attenuation for Chamoli was much higher compared to those for Garwhal-Kumaun region using general seismicity data. At higher frequencies intrinsic attenuation for Chamoli is lower than and scattering attenuation is comparable to those obtained using general seismicity data of Garwhal-Kumaun region.301 64 - PublicationRestrictedCrustal seismic anisotropy beneath Shillong plateau - Assam valley in North East India: Shear-wave splitting analysis using local earthquakes(2017-08-24)
; ; ; ; ; ; ; ; ;; ; ; ;We present crustal anisotropy estimates constrained by shear wave splitting (SWS) analysis using local earthquakes in the Shillong plateau and Assam valley area, North East India (NE India) region. Splitting parameters are determined using an automated cross-correlation (CC) method. We located 330 earthquakes recorded by 17 broadband seismic stations during 2001–2014 in the study area. Out of these 330 events, seismograms of 163 events are selected for the SWS analysis. Relatively small average delay times (0.039–0.084 s) indicate existence of moderate crack density in the crust below the study area. It is found that fast polarization directions vary from station to station depending on the regional stress system as well as geological conditions. The spatial pattern of crustal anisotropy in the area is controlled mostly by tectonic movement of the Indian plate towards NE. Presence of several E-W and N-S trending active faults in the area also play an important role on the observed pattern of crustal anisotropy.201 3