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Array detection and location of core shadow events

NUCLEAR PHYSICS DIVISION BHABHA ATOMIC RESEARCH CENTRE, BOMBAY, India

Abstract

The spectral features and slowness vector of the PKIKP and PP signals recorded clearly at the Gauribidanur Seismic Array (GBA) from four underground explosions (m_b = 5.6, 5.9, 6.2 and 6.6) at the Nevada Test Site (NTS) were studied in detail. From the spectral similarity which characterizes their phase-summed signals, in the band 0.5 cps to 1.5 cps, it has been possible to synthesize reference signals, corresponding to these phases. By "chirping" these signals against the appropriately-phased array beams, the onset of these phases were identified for such events down to m_b = 5.3.

Application of techniques of velocity and frequency filtering to the GBA records corresponding to 16 well-recorded NTS events ( 127.7° and the San Fernando earthquake of February 9, 1971 129.9°) has failed to reveal any precursor to the principal PKP phase which corresponds to the DF branch (PKIKP) of the Bolt (1968) curve. It is found that only the PP phase shows significant spectral differences between the earthquake and the set of explosions investigated.

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				A. C. CHANG and J. R. CLEARY Precursors to PKKP Bulletin of the Seismological Society of America, August 1, 1978; 68(4): 1059 - 1079. [Abstract] [PDF]