Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003geoji.152f...1n&link_type=abstract
Geophysical Journal International, Volume 152, Issue 2, pp. F1-F7.
Astronomy and Astrophysics
Astronomy
2
Crust, Nuclear Explosions, Refraction Seismology, Scattering, Seismic-Wave Propagation, Upper-Mantle
Scientific paper
Teleseismic Pn phases with a long, high-amplitude coda, are observed to offsets >3000 km along the Peaceful Nuclear Explosion seismic profiles Quartz and Ruby. For the high-frequency (>5 Hz) part of the Quartz data, which is shown here, coda lengths of more than 10 s can be visually observed in the seismic sections. We interpret the teleseismic Pn arrivals as multiple sub-Moho refractions (whispering-gallery phases), which travel over large distances due to a positive upper-mantle velocity gradient. The coda of these arrivals is explained by lower crustal scattering of the whispering-gallery phases from the mantle. The modelling is based on calculation of reflectivity and 2-D visco-elastic finite-difference synthetic seismograms. Our models are in agreement with other deep seismic data from continental areas, which typically show a reflective lower crust and an almost transparent uppermost mantle. The lower crustal heterogeneity is described by von Karman distribution with a standard deviation of 0.5 km s-1 for the P-wave velocity and correlation lengths of 2.4 km (horizontally) and 0.6 km (vertically). The positive vertical upper-mantle velocity gradient of ~0.004 km s-1 km-1, which is characteristic for profile Quartz, forms a waveguide which gives rise to the teleseismic Pn. It is not necessary to include upper-mantle heterogeneity in order to explain the characteristics of this arrival.
Morozov Igor B.
Nielsen Lance
Smithson Scott B.
Solodilov Leonid
Thybo Hans
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