HR: 1340h
AN: S23B-0330    [Abstracts]
TI: How do underground explosions excite regional waves: a source array analysis by virtue of a reciprocal theorem
AU: * Hong, T
EM: tkhong@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AU: Xie, J
EM: xie@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AB: There has been a long-standing question on how the regional S waves are generated by underground nuclear explosions (UNEs). Hundreds of historic UNEs were recorded by individual seismic stations at regional distances. According to the reciprocal theorem (Aki and Richards, 1980), the records can be treated as those collected from a fictitious array at the sources. Array analysis techniques can then be applied to these records to infer the phase velocity composition of regional waves in the near-source region, and constrain the excitation mechanisms. We apply a frequency-wavenumber technique for the array analysis, and analyze short-period records of Balapan explosions from the Borovoye Observatory in Kazakhstan at distances of around 690 km. Pn wave is composed of P wavelets leaving the source region with phase velocities of about 8.0 km/s. P wavelets dominate the seismograms between Pn and Sn. S wavelets with phase velocities of about 4.0 km/s start to emerge in the Sn window, where the dominant energy still originates from P. Toward later Sn coda, the influence of S wavelets increases with time. The Lg waves are built mostly by waves with velocities of about 4.0 km/s, which corresponds to the S phase velocity. The dominant phase velocity in the Rg window is 3.1 km/s. It seems that Rg scattering plays a relatively trivial role in the shear wave development by Balapan explosions. Primary phases (Pn, Sn and Lg) are composed mainly of wavelets leaving the sources along the great-circle direction, while coda waves are increasingly influenced by randomly scattered waves.
DE: 7219 Nuclear explosion seismology
DE: 7294 Instruments and techniques
DE: 7203 Body wave propagation
DE: 7205 Continental crust (1242)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting