Research Article| December 24, 2013 Estimation of Source Parameters, Quality Factor (QS), and Site Characteristics Using Accelerograms: Uttarakhand Himalaya Region Jyoti Sharma; Jyoti Sharma aInstitute of Seismological Research (ISR), Department of Science and Technology, Government of Gujarat, Village—Raisan, Gandhinagar, Gujarat 382009, Indiajyotisharmaiitkgp@gmail.com Search for other works by this author on: GSW Google Scholar Sumer Chopra; Sumer Chopra bMinistry of Earth Sciences (MoES), Government of India, Prithvi Bhavan, Seismology Division, Lodhi Road, New Delhi 110003, India Search for other works by this author on: GSW Google Scholar Ketan Singha Roy Ketan Singha Roy aInstitute of Seismological Research (ISR), Department of Science and Technology, Government of Gujarat, Village—Raisan, Gandhinagar, Gujarat 382009, Indiajyotisharmaiitkgp@gmail.com Search for other works by this author on: GSW Google Scholar Author and Article Information Jyoti Sharma aInstitute of Seismological Research (ISR), Department of Science and Technology, Government of Gujarat, Village—Raisan, Gandhinagar, Gujarat 382009, Indiajyotisharmaiitkgp@gmail.com Sumer Chopra bMinistry of Earth Sciences (MoES), Government of India, Prithvi Bhavan, Seismology Division, Lodhi Road, New Delhi 110003, India Ketan Singha Roy aInstitute of Seismological Research (ISR), Department of Science and Technology, Government of Gujarat, Village—Raisan, Gandhinagar, Gujarat 382009, Indiajyotisharmaiitkgp@gmail.com Publisher: Seismological Society of America First Online: 14 Jul 2017 Online ISSN: 1943-3573 Print ISSN: 0037-1106 Bulletin of the Seismological Society of America (2014) 104 (1): 360–380. https://doi.org/10.1785/0120120304 Article history First Online: 14 Jul 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Jyoti Sharma, Sumer Chopra, Ketan Singha Roy; Estimation of Source Parameters, Quality Factor (QS), and Site Characteristics Using Accelerograms: Uttarakhand Himalaya Region. Bulletin of the Seismological Society of America 2013;; 104 (1): 360–380. doi: https://doi.org/10.1785/0120120304 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin of the Seismological Society of America Search Advanced Search Abstract A study of source, path, and site characteristics was conducted for the Uttarakhand Himalaya region using accelerogram data from 15 earthquakes (ML≥3.5). These earthquakes were recorded at the 16‐station accelerograph network operated by the Indian Institute of Technology, Roorkee, during 2005–2011. The average seismic moment (M0) of the studied earthquakes ranges between 1.20×1022 and 1.02×1024 dyn·cm, and the average moment magnitude (Mw) is between 4.0 and 5.3. The estimated corner frequency (fc) varies from 1.1 to 3.3 Hz, radius of rupture (rd) from 0.5 to 1.4 km, and stress drop (Δσ) from 6 to 172 bars, indicating continuous seismic energy release in the Uttarakhand region. The interdependence between estimated source parameters is shown by determining scaling laws for the studied region. The constant Q0 of the shear‐wave quality factor (QS=Q0fn) varies between 40 and 300 and exponent n varies between 0.85 and 1.5, providing an average relation of QS=174f1.27. However, least‐square fitting of the observed data set in the frequency range 0.1–20 Hz gives QS as 159f1.16. The value of QS demonstrates that the region is heterogeneous, seismically active, and attenuative. The high‐frequency spectral fall‐off factor (γ) varies from 1.3 to 2.1 and the upper crustal attenuation factor (κ) from 0.023 to 0.07 s at different sites, with an average of 0.044 s. The site response characteristics are estimated by horizontal‐to‐vertical spectral ratio (HVSR) and generalized inversion (GINV) techniques; results obtained from both the techniques show 1:1 correspondence. The site amplification factor varies between 2.3 and 9.4 using HVSR and between 2.6 and 10.9 using GINV among different stations. The predominant frequency ranges from 1.3 to 8.3 Hz with HVSR and from 1.3 to and 9.0 Hz with GINV.Online Material: Tables of source, path, and site parameters with associated errors at different sites for the earthquakes recorded from December 2005 to March 2011. Figures represent accelerogram records, source spectra matching, and site amplification patterns. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
We estimated ground motions at 12 selected sites in the Kachchh rift basin of Gujarat in the western peninsular shield area of India, where the damaging 1956 Anjar earthquake ( M w 6.0) was experienced. The ground motions are estimated by applying the empirical Green’s function approach using an earthquake of M w 4.5, which occurred on the inferred rupture plane of the Anjar earthquake with a nearly similar fault mechanism. The estimated peak ground acceleration (PGA) varies between 114 and 22 cm/s2 at these sites, located at distances of 21–127 km from the epicenter, respectively. The maximum accelerations are correlated with the modified Mercalli intensity reported for the Anjar earthquake using the empirical relationship between the PGA and intensity. At most of the sites, the level of acceleration could explain the reported damage. At a few sites, the instrumental intensity estimated using the acceleration values obtained from the synthesis is larger than the felt intensity. The ground‐motion prediction equation (GMPE) developed for the region estimates the maximum PGA near the epicenter area in the 250–300 cm/s2 range, and the acceleration obtained by our analysis is found to be closer to the predicted acceleration obtained by GMPE. Our analysis assesses the level of ground motion that was experienced during the 1956 Anjar earthquake fairly well and corroborates that reasonable prediction of the ground motion of a historical earthquake is achievable, if strong‐motion recordings are available from the rupture plane of the historical earthquake.
Abstract In the present study the attenuation of seismic-wave energy in and around the source area of the Chamoli Earthquake of 29 March 1999 is estimated using 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. The method of a single backscattering model is employed to calculate frequency dependent values of coda Q ( Q c ). A total of 30 aftershock events are used for Q c estimation at central frequencies 1.5, 3, 6, 9, 12, 18, and 24 Hz through five lapse-time windows from 10 to 50 sec starting at double the travel time of the S wave. The observed Q c is strongly dependent on frequency, which indicates that the region is seismically and tectonically active with high heterogeneities. The variation of Q c has also been estimated at different lapse times to observe its effect with depth. The variation of Q c with frequency and lapse time shows that the lithosphere becomes more homogeneous with depth. Q c -values for higher frequencies increase very fast with depth within about the top 63 km of the lithosphere and then become more or less constant beyond this depth. This indicates that turbidity at higher frequency decays very fast with depth, and the mantle may be transparent to high-frequency waves. The variation of Q c at 1.5 Hz with lapse time matches quite well with those predicted by Gusev (1995). However, the frequency parameter n in the relation Q c = Q 0 f n , where Q 0 = Q c at 1 Hz, does not follow the expected pattern given in his model. This could be due to faster depth decay of turbidity as mentioned previously.
The existing seismological network in the Kangra-Chamba sector has been upgraded with 12 three-component digital seismometers to obtain new insight on the nature and sources of continued clustered seismicity in this part of northwest Himalaya. A combination of travel-time-distance plots and travel-time inversion of P and S phases have been used to derive a 1D velocity model for the region. The mini- mum 1D velocity model divides the average 44 km thick crust into four layers. The top ∼10 km thick layer represents the metamorphosed sediments of the Chamba nappe that dominates the surface geology of the study area. Suggestion of a thin low-velocity layer at 15 km depth possibly marks the detachment zone separating the downgoing Indian plate from the overriding wedge. The improved locations of epicenters show close clustering of seismic events immediately northeast of the epicenter of the 1905 Kangra earthquake, while away from this zone the seismicity in the Chamba sector has more even distribution. In the later sector, space-depth distribution of hypocenters suggests that strain resulting from the ongoing collision of the Indian plate with Asia is being consumed by reverse-fault movement on the Chamba thrust. The clustered seismicity in the Kangra sector has three distinct source regions and mechanisms: (1) southward displacement of the thick Chamba nappe sheet over the Panjal imbricate zone along the Panjal thrust accounts for the seismicity at shallow depths of less than 7 km, (2) the nucleation of strains where the northeast dipping main boundary thrust (MBT) merges with the detachment plane produces focused seismicity near this junc- tion, and (3) the seismicity in a small pocket below the plane of detachment appears to be a consequence of stresses generated at the base of the northeast dipping detachment plane by the transverse structure.
Abstract Scapolite occurrences are widely observed in the metasedimentary rocks exposed around the Khetri Copper Belt and adjoining Nim ka Thana copper mineralized area in western India. Amoeboidal to well-developed and rounded/elliptical-shaped marialitic scapolite (Na-rich end-member) rich zones with variable Cl contents ranging from 1.0 wt % to 2.9 wt % have been identified in proximity to the ore-bearing hydrothermal fluid activity zones. Although scapolite is formed as a product of regional metamorphism in many places, in this study, we propose a strong possibility that scapolite was formed by hydrothermal ore-bearing fluid interaction with metasediments. The evidence of hydrothermal activity and Cl sourcing is attributed to (i) the absence of evaporite beds in the area and no Na-rich plagioclase as inclusions within the scapolite suggesting the formation of marialitic scapolite from sodic plagioclase in the metasediments with the interacting hydrothermal fluid; (ii) an epithermal to mesothermal hydrothermal fluid with moderate salinity responsible for the Cu mineralization that is ascribed to be the source of Cl for the formation of marialitic scapolite; (iii) diffusion of SO 2 in the scapolite in close association with the sulfide mineral phase (chalcopyrite) supporting the involvement of ore-bearing fluid in the development of scapolite; (iv) the absence of zoned scapolite, the spatial distribution of scapolite in a particular lithology, the occasional incorporation of sulfur into marialitic scapolite and the texture/geometry in the scapolite suggesting a broad hydrothermal linkage instead of a pure metamorphic origin.
Abstract The Deccan volcanic province (DVP) witnessed a massive outpouring of flood basalts of ∼2 million km 3 volume, at ∼65 Ma, in less than a Myr. The volcanic eruption is concomitant with crustal extension, lithospheric thinning and magma influx beneath the major rift systems namely Cambay, Narmada, and Kutch. In this study, we investigate the anisotropic and isotropic variations within the crust and upper mantle beneath the northwestern DVP by estimating the shear wave velocity ( V SV , V SH , and V Soigt ) and radial anisotropy ( ξ oigt ) models using the Surface Wave Tomography technique. A joint inversion of the regionalized Rayleigh and Love wave group velocities is performed, using the genetic algorithm approach. Our results reveal different intracrustal layers, lid, and a low‐velocity zone (LVZ). This LVZ comprises of a uniform asthenospheric low‐velocity layer (LVL) of average V SV 4.44 km/s and V SH 4.47 km/s, and another LVL below, of average V SV 4.45 km/s and V SH 4.41 km/s. Furthermore, the LVZ represents a negative anomaly with reference to different global models (AK135, STW105, PREM, and S2.9EA). A negative ξ oigt is observed in the LVZ, indicating dominance of vertical flow. This could be related to presence of partials melts, volatile materials and/or a thermal anomaly. We also identified the Moho (∼34–40 km) and lithosphere‐asthenosphere boundary (∼84–123 km). The low V S values, negative ξ oigt and a thin lithosphere (∼84 km) in the vicinity of Gulf of Cambay affirm the presence of a plume head beneath it, in concurrence with the hypothesis of Indian Plate‐Reunion plume interaction.
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