Pn wave velocity and Moho geometry in north eastern India

  • S. S. Rai
  • K. S. Prakasam
  • N. Agrawal


Pn velocity has been computed across the NE India and Moho geometry constrained, using regional earthquake travel times recorded by a network of 30 seismological stations operated during February-May 1993. Using an appropriate velocity model and the arrival times at the network stations, preliminary hypocentres of 16 regional earthquakes provided by NEIC were also improved. The average Pn wave velocity in NE India has been found to be 8.5 ±0.2 km/s. It varies from 8.3 to 8.5 km/s beneath the Shillong Plateau, Mikhir hills and Assam valley, which is significantly higher than those in other parts of India. The crustal thickness in NE India is also high, varying from 45–49 km under the Shillong plateau and the adjoining region to 55–65 km in the convergence zone. The presence of a thick crust and high Pn velocity suggests that the lithosphere in NE India is colder, as also indicated by the observed deeper level (45-51 km) seismicity of the region.


NE India seismicity crust travel time time term 


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  1. Braile L W, Hinze W J, Van Frese and Keller G R 1989 Seismic properties of crust and uppermost mantle of the conterminous United States and adjoining Canada, in Geophysical Framework of United States (ed.) L C Parkiser and W D MooneyMem. Geological Soc. Am. 172 655–680Google Scholar
  2. Chen W P and Molnar P 1990 Source parameters of earthquakes and intraplate deformation beneath the Shillong plateau and the northern Indo Burmese ranges;J. Geophys. Res. 95 12527–12552CrossRefGoogle Scholar
  3. Evans P 1964 The tectonic framework of Assam;J. Geol. Soc. India 5 80–96Google Scholar
  4. Gaur V K and Bhattacharji J C 1983 Gravimetric determination of the shape of Moho in peninsular and NE India, IUGG Assembly, Hamburg, Germany, August, 15–27Google Scholar
  5. Gupta H K, Singh S C, Dutta T K and Saikia M M 1984 Recent investigation in NE Indian Seismicity, inProc. Intl. Symp. on continental seismicity and earthquake prediction, (Beijing: Seismological Press) 63–71Google Scholar
  6. Hearn T M 1984 Pn travel times in south California;J. Geophys. Res. 89 1843–1855CrossRefGoogle Scholar
  7. Kayal J R and De R 1987 Pn velocity study using a temporary seismographic network in the Shillong plateau, NE India;Bull. Seism. Soc. Am. 77 1718–1727Google Scholar
  8. Kind R 1972 Residual and velocity of Pn waves recorded by the San Andreas seismograph network;Bull. Seism. Soc. Am. 62 85–100Google Scholar
  9. Mukhopadhyay S, Khattri K N and Chander R 1995 Seismic velocity and related elastic parameters of the crust in the Shillong massif;J. Himalayan Geology 6 1–8Google Scholar
  10. Nandy D R 1980 Tectonic patterns in northeastern India;Indian J. Earth Sci. 7 103–107Google Scholar
  11. Openheimer D H and Eaton J P 1984 Moho orientation beneath central California from region earthquake travel times;J. Geophys. Res. 89 10267–10282CrossRefGoogle Scholar
  12. Ravi Shankar 1988 Heat flow map of India and discussion on its geological and economic significance;Indian Minerals 42 89–110Google Scholar
  13. Scheidegger A E and Willmore P L 1957 The use of least squares method for the interpretation of data from seismic surveys;Geophysics 22 9–22CrossRefGoogle Scholar
  14. Shearer P M and Openheimer D H 1982 A dipping Moho and crustal low velocity zone from Pn arrivals at Geysers, Clear lake, California;Bull. Seism. Soc. Am. 72 1557–1566Google Scholar
  15. Sitaram M V D and Saikia M M 1992 Results of a seismic network in NE India;Curr. Sci. 62 177–182Google Scholar
  16. Tandon A N 1954 A study of Assam earthquake of August 1950 and its aftershocks;Indian J. Meteorol. Geophys 5 95–137Google Scholar
  17. Verma R K and Mukhopadhyay M 1977 An analysis of the gravity field in northeastern India;Tectonophysics 42 283–317CrossRefGoogle Scholar

Copyright information

© Indian Academy of Sciences 1999

Authors and Affiliations

  • S. S. Rai
    • 1
  • K. S. Prakasam
    • 1
  • N. Agrawal
    • 2
  1. 1.National Geophysical Research InstituteHyderabad
  2. 2.Pan India Consultants Pvt. Ltd.Gurgaon, Haryana

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