Spectral characteristics of the 11 May 1998 Pokhran and 28 May 1998 Changhai nuclear explosions

摘要

The concept of spectral magnitudes and spectral seismograms, recently developed utilizing broadband seismic data permits finer insight into the seismie-source processes. It has been observed that on a spectral seismogram display, nuclear explosions have peak energy content in higher frequencies compared to earthquakes of the same magnitude at similar distances. The broad-band GEOSCOPE seismic station (HYB) at NGRI, Hyderabad, recorded the Pokhran explosion of 11 May 1998 as well as the Chaghai explosion of 28 May, 1998. These two explosive sources exhibit a distinct difference in the energy contents in various frequency ranges. The Chaghai source had more energy in lower frequencies compared to the Pokhran sources. To ensure that this observation is not specific to the recording site, we analysed records of the newly established broad-band seismic stations of the India Meteorological Department. The intrinsic differences in their spectral characteristics are confirmed by this comparative study. We note that energy from the Pokhran event peaked in the frequency range of 3.5 to 6 Hz compared to a range of 1 to 3 Hz for the Chaghai explosion.