When locating globally, the program uses the IASPEI91 travel time software described by Buland and Chapman (1983) and Kennett and Engdahl (1991). The global model is used if the distance indicator in the S-file is D. If the distance idicator is R, the local model is used unless there are distant stations (distance larger then TEST(57) in which case the global model is used.
HYP evaluates all the IASPEI91 phases (up to 60) at each delta, and searches for the phase specified in the 4-character phase identifier. If no phase is found, the phase is given a weight of -1, which effectively removes it from the phase set. If a phase is labeled as 'P ', 'S ', 'PKP ' or 'SKS ', and this phase is not in the IASPEI91 list, the first arrival phase having P or S as its first letter is used, or PKP, SKS as its first 3 letters. In addition, include the PKiK phases in this search for 'PKP ' and 'SKiK' phases in the search for 'SKP '. The IASPEI91 phase set currently includes: P, Pdiff, PKP, PKiKP, pP, pPdiff, pPKP, pPKiKP, Sp, sPdiff, sPKP, sPKiKP, PP, P'P', S, Sdiff, SKS, sP, pSdiff, pSKS, Ss, sSdiff, sSKS, SS, S'S', PS, PKS, SP, SKP, SKiKP, PcP, PcS, ScP, ScS, PKKP, PKKS, SKKP, and SKKS.
Long phase names:
Normally SEISAN and the Nordic format assume up to 4 character phase names. However, when working with global phases, the phase name length can in a few cases be up to the ISC standard of 8 characters. The program then uses column 9 for weight (normally blank) and column 11-18 for the phase. In this case it is not possible to give a polarity.