Bulletin of the Seismological Society of America
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Bulletin of the Seismological Society of America; April 2009; v. 99; no. 2A; p. 705-725; DOI: 10.1785/0120080025
© 2009 Seismological Society of America
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Modeling of Strong-Motion Data in Northeastern India: Q, Stress Drop, and Site Amplification

S. T. G. Raghukanth* and Surendra Nadh Somala

Department of Civil Engineering, Indian Institute of Technology, Guwahati Assam, India rk{at}iitg.ernet.in

* Present address: Department of Civil Engineering, Indian Institute of Technology, Madras, Chennai, India; raghukanth@iitm.ac.in.

In this article point source seismological model is used to model the available strong-motion accelerograms in northeastern India. Key seismic parameters such as Quality factor (Q-value), kappa factor ({kappa}0), site amplification, and stress drop are derived from the strong-motion data. A total of 111 three-component records coming from seven earthquakes with magnitudes ranging from Mw 5.2 to 7.2 are used in obtaining the source and path parameters. The Q-value of the Indo–Burma tectonic domain, which is a subduction zone, is obtained as 431f0.7. For the Bengal basin–Shillong plateau region the Quality factor is estimated as 224f0.93. The kappa factors for vertical and horizontal components are obtained as 0.013 and 0.033 for soft rock type sites. For firm ground sites {kappa}0 is estimated as 0.025 for vertical and 0.041 for horizontal components, respectively. The site amplification functions for soft rock and firm ground conditions are found from the horizontal-to-vertical ratio. The obtained stress drops of the seven events lie between 128 and 282 bars. The source parameters obtained in this study provide a useful framework for working out ground-motion relations in northeastern India.






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