Sn 1


Sn 1 :

Early use of the designation Sn was in reference to short-period S waves that were presumed to propagate as head waves along the top of the mantle. The new IASPEI standard phase names define Sn as any S wave bottoming in the uppermost mantle or an upgoing S wave from a source in the uppermost mantle, see also the discussion about the analogues defined phase Pn. Quite commonly, the term is now also applied to a prominent arrival of short-period shear waves that may be observed (with a straight-line travel-time curve) at epicentral distances as great as 40o. Although Sn arrives at regional distances larger some 100 km usually as the first S-wave arrival its amplitudes are, as compared to the later Sg, SmS, Lg arrivals, relatively small and often covered in the signal generated noise after Pg. For record examples see, e.g., Figs. 1a, 3a, 4a, 6a, and 6c in DS 11.1 of this Manual and Kulhánek (2002). For this and other such symbols used in seismic phase names see IS 2.1 in this Manual and Storchak et al. (2003 and 1011)

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