The recent Indian nuclear tests - a seismic overview

Abstract

This paper reviews the seismic analysis of the close-in, regional and teleseismic data corresponding to May 1998 Indian nuclear tests. Strong Lg and Rayleigh waves (period 3.5–7 s) were observed at several incountry stations from the two large explosions of 11 May 1998 (POK2). The magnitude of POK2 based on regional Lg wave data was obtained as 5.47 ± 0.06. A comparison of Lg waves at Gauribidanur array (GBA), India corresponding to POK2 with that of the Indian explosion of May 1974 (POK1) gave a yield ratio of 4.83 between these events, which is very near to the value of 4.46 obtained from the differences in m_b values between POK2 and POK1. Analysis of regional Rayleigh waves provided a M_s value of 3.56 for POK2 and also revealed that Nuttli’s relation for estimation of surface wave magnitude based on eastern North American data is also applicable to Indian region. The yield estimates of POK2 from the teleseismic, regional and close-in seismic data, were found to be consistent with those obtained from the post-shot radio-chemical measurements. The analysis of spectrograms generated from seismograms of POK2 and Pakistan explosion of 28 May 1998 showed that the ratio of source energies between these events is higher than what was obtained from global m_b values.