First-arriving P-type phases (P, Pn, Pb, Pg) are picked more accurately than later phases, so their measurement error estimates are the smallest, 0.8 s.
The measurement error for first-arriving S-phases (S, Sn, Sb, Sg) is set to 1.5 s.
Phases traversing through or reflecting from the inner/outer core of the Earth have somewhat larger (1.3 s for PKP, PKS, PKKP, PKKS and P’P’ branches as well as PKiKP, PcP and PcS and 1.8 s for SKP, SKS, SKKP, SKKS and S’S’ branches as well as SKiKP, ScP and ScS) measurement error estimates to account for possible identification errors among the various branches.
Free-surface reflections and conversions (PnPn, PbPb, PgPg, PS, PnS, PgS and SnSn, SbSb, SgSg, SP, SPn and SPg) are observed less frequently and with larger uncertainty,
and therefore suffer from large, 2.5 s, measurement errors. Similarly, a measurement error of 2.5 s is assigned to the longer period and typically emergent diffracted phases (Pdif, Sdif and PKPdif).
The a priori measurement error for the commonly observed depth phases (pP, sP, pS, sS and pwP) is set to 1.3 s, while for the rest of depth phases(pPKP,sPKP,pSKS,sSKSbranchesandpPb,sPb,sSb,pPn, sPn, sSn)
the measurement error estimate is set to 1.8 s. We set the measurementerrorestimateto2.5sforthelessreliabledepthphases (pPg, sPg, sSg, pPdif, pSdif, sPdif and sSdif).
Note that we also allow for distance-dependent measurement errors. For instance, to account for possible phase identification errors at far-regional distances the a priorimeasurement error for Pn and P is increased from 0.8 to 1.2 s and for Sn and S from 1.5 to 1.8 s between 15 and 28◦
. The measurement errors between 40 and 180◦ are set to 1.3 and 1.8 s for the prominent PP and SS arrivals, respectively, but they are increased to 1.8 and 2.5 s between 25 and 40◦.
