Crustal seismic anisotropy beneath Shillong plateau - Assam valley in North East India: Shear-wave splitting analysis using local earthquakes

Sharma, Antara; Baruah, Santanu; Piccinini, D.; Saikia, Sowrav; Phukan, Manoj K.; Chetia, Monisha; Kayal, J. R.

doi:10.1016/j.tecto.2017.08.027

Cited by 14 publications

(14 citation statements)

References 66 publications

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“…Anisotropy is also observed in the crust as inferred from analysis of shear waves of local earthquakes. Few interesting findings include those obtained from aftershock records of the 2001 Bhuj earthquake in western India (Padhy and Crampin, 2006;Mandal, 2009) and data recorded by a cluster broadband network in northeast India region (Sharma et al, 2017). The crustal anisotropy may be stress induced or structure related.…”

Section: Seismic Anisotropymentioning

confidence: 95%

Seismicity and structure of the Indian subcontin

Kayal

2020

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Instrumentally recorded tectonic earthquakes The 1897 great Shillong plateau earthquake (M w 8.1) in NE India region is the first instrumentally recorded Indian earthquake that was registered outside India by a few global seismic stations. After this great event, the first Indian seismological observatory was established in Alipore (Kolkata) in 1899 under auspices of the India Meteorological Department (IMD) (Kayal, 2008). Since then the national seismological network is developed; today it consists of some 115 broadband seismic observatories including some cluster-networks in NE India and in different segments of the Himalayas. In addition to these, a cluster of some 21 broadband stations is in operation in Koyna-Warna region and a cluster of some 50 broadband and 50 strong-motion stations is in operation in Gujarat state under the auspices of the Institute of Seismological Research (ISR), a newly established Institute in 2006. With the upgraded national network, earthquakes down to magnitude M w 3.5 are fairly well located, and down to M w 2.0 by the cluster networks. Recently, the Ministry of Earth Sciences (MoES) established the National Centre for

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Section: Seismic Anisotropymentioning

confidence: 95%

Seismicity and structure of the Indian subcontin

Kayal

2020

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“…We have discussed the detailed analysis of crustal shear wave splitting in our earlier work (Sharma et al 2017). Out of 215 well located events, 163 events fulfilled the criteria for the analysis.…”

Section: Anisotropy Analysismentioning

confidence: 99%

“…A time window length of about 0.3 s was selected, fixing the start of the windows 0.1 s before the S arrival pick. To ensure consistency of the results we considered only those measurements that showed a CC coefficient larger than or equal to 0.7 (Sharma et al 2017). Figure 2 illustrates the average fast polarization of shear-wave and time delay of slow shear waves.…”

Section: Anisotropy Analysismentioning

confidence: 99%

“…In a recent work on crustal seismic anisotropy, Sharma et al (2017) reported local crustal anisotropic characteristics in Shillong-Mikir plateau but shedding no light on the stress tensor behavior. In the present study, we try to investigate the localized seismic stress pattern around 17 seismic stations by Stress Tensor Inversion (STI) technique.…”

Section: Introductionmentioning

confidence: 99%

“…Shear wave splitting helps to understand characteristics of anisotropy in the crust below seismic stations. A detailed description of the method, analysis and results is given in our earlier work (Sharma et al 2017).…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Correlation between crustal anisotropy and seismogenic stress field beneath Shillong–Mikir Plateau and its vicinity in North East India

Baruah

Sharma

Dey

et al. 2021

Geomatics, Natural Hazards and Risk

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A systematic study towards understanding the correlation between polarization direction of crustal anisotropy with seismogenic stress field at different locations of the Shillong-Mikir Plateau and its vicinity in North East India is attempted. We used data from a 17-station broadband seismic network. In our earlier work , crustal anisotropic parameters were determined using ANISOMAT þ for the 17 seismic stations. In this study, we have estimated stress field around the stations using focal mechanism solutions (FMS). Some 215 FMS are obtained by waveform inversion. These solutions are used for stress tensor inversion to estimate stress field around each location. It is observed that polarization direction of crustal anisotropy is consistent with that of the maximum horizontal stress ( Ơmax ) as well as the minimum horizontal stress ( Ơ min ). In addition to this, two orthogonal fast polarizations in some locations are also noted. The bivariate nature of correlations helps us to understand that the major mechanisms of seismic crustal anisotropy are not only due to the regional stress, but active faults and other geological conditions play a significant role in contemporary orientation of seismic crustal anisotropy and seismogenic stress field.

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Along‐strike variation in the shear wave crustal structure of the NE Himalayan and Indo‐Burmese arc: Evidence based on surface wave dispersion analysis

Chanu

Kumar

Kumar³

et al. 2022

Geological Journal

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Surface wave dispersion data is used to infer the shear wave velocity structure variation in the north‐east Himalaya and Indo‐Burmese arc regions. We have used 25 earthquakes data from four groups with a magnitude range of 5.0–6.7, epicentral distance range 368–800 km, and focal depth less than 50 km. Ray paths from the earthquake location to the seismic station are transversely passing different geotectonic units of the Himalayas, Indo‐Gangetic plains, and Indo‐Burma collision zones. The weighted average dispersion curve and the path averaged shear wave velocity models are computed for the four groups located at different azimuths around Shillong seismic station. Non‐linear least‐square inversion is performed to obtain the shear wave velocity structure of the crust and uppermost mantle from joint inversion of Rayleigh and Love waves group velocities. Subsequently, Rayleigh and Love waves group velocities are inverted separately to obtain vertical and horizontal components of S‐wave velocity. Next, using these components anisotropy coefficient values at different depths for each path are also estimated. A high variation of dispersion curves and the shear wave velocity models from one group to another indicates that the region is geotectonically very complex. An approximately 80 km‐thick zone beneath the study region has shear wave velocity as low as 1.7 km/s in the uppermost crust in the southern part and ~4.7 km in the uppermost mantle beneath the Eastern Himalayan Syntaxis (EHS). Inferred velocity is also lower than that of PREM and AK135 global models with a much thicker crust beneath the study region. Radial anisotropy varies even within the northern part from the Indo‐Eurasian collision zone to EHS and northern to southern Indo‐Burma ranges. Anisotropy is comparatively stronger in the deeper part below ~40 km for the three paths, except for the EHS, where the result is contrary.

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Crustal seismic anisotropy beneath Shillong plateau - Assam valley in North East India: Shear-wave splitting analysis using local earthquakes

Cited by 14 publications

References 66 publications

Seismicity and structure of the Indian subcontin

Seismicity and structure of the Indian subcontin

Correlation between crustal anisotropy and seismogenic stress field beneath Shillong–Mikir Plateau and its vicinity in North East India

Along‐strike variation in the shear wave crustal structure of the NE Himalayan and Indo‐Burmese arc: Evidence based on surface wave dispersion analysis

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