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  • Nomenclature of Seismic Phases

    Contents


    Near-earthquake phases

    Pn, Sn
    Longitudinal and transverse waves refracted below the Mohorovicic discontinuity (head waves).
    Pg, Sg (or p, s)
    Waves in the upper crust.
    Pb, Sb (or P*, S*)
    Waves in the lower crust or along the Conrad discontinuity.
    PmP, SmS
    Waves reflected from the Mohorovicic discontinuity.

    Phases of distant shallow earthquakes

    P, S
    Direct longitudinal or transverse waves.
    PKP (or P')
    Direct longitudinal waves traversing the Earth's core without detailed identification.
    PKIKP (or P')
    Core P phase through the inner core.
    PKhKP
    Core phase due to reflections or scattering arriving before PKIKP.
    PKJKP
    Core phase with an S-wave portion of the path through the inner core.
    PKiKP
    Core wave reflected from the inner core.
    PP, PPP, SS, SSS
    P or S waves reflected once or twice at the Earth's surface.
    PcP, ScS
    P or S waves reflected at the Earth's core boundary.
    PcS, ScP
    P or S waves transformed on reflection at the Earth's core.
    PKKP (PK2P)
    P waves reflected from the inside surface of the core, thereby passing twice through the core.
    PKjP
    P waves reflected j-1 times from the inner surface of the core, thus passing j times within the core.
    P'P' (PKPPKP)
    PKP waves reflected from the Earth's surface, passing twice through the core.
    SKS
    S waves passing through the core as P waves, transformed back into S waves on emergence.
    SKKS (SK2S)
    S waves transformed on refraction at the core boundary into P waves, reflected from the inside surface of the core and finally transformed back into S waves at the core boundary.
    PS, SP, PPS, SPP, PSPS, PPSS, SPSP, etc.
    P and S waves reflected and transformed at the Earth's surface.
    SKP
    S wave transformed into P on refraction into the core.
    PKS
    P wave transformed into S on refraction when leaving the core. The principle of classification may be extended to cover many other sequences of reflection and transformation, as in SKKP, PcPP, ScSScS, etc.
    PdP
    A wave of PP type reflected or scattered at the underside of a discontinuity at depth d in the Earth's mantle (Bolt, 1970).
    Pc
    P waves diffracted around the Earth's core.
    Sc
    S waves diffracted around the Earth's core.

    Phases of deep-focus earthquakes

    The major branches of the travel-time curves carry the same descriptions as for shallow-focus events. Waves leaving the focus in an upward direction, and reflected at the surface are described by the letters p, s, as follows:

    pP, pPKP, sP, sPP, etc.
    P or S waves reflected from the surface as P waves.
    pS, sS, pSS, etc.
    P or S waves reflected from the surface as S waves.

    Surface waves

    L
    Long waves, unidentified, the beginning of the surface wave group.
    G
    A group of long-period Love waves often in the form of a large pulse for transoceanic paths.
    LQ
    Love waves.
    LR
    Rayleigh waves.
    Lg
    Crustal channel wave with characteristics similar to surface waves, it travels only along continental paths; in research papers the subdivision is more detailed (Lg1, Lg2, Li, Rg) (Bath, Oliver).
    Lm, Qm, Rm
    Waves of maximum amplitudes in the surface wave group.
    Rj, Gj (j = 1, 2, …)
    Trains of Rayleigh or mantle Love waves that have travelled successive arcs around the great circle to the station. R1, R3, …, etc., denote the direct or minor arc; R2, R4, …,etc., denote the major arc.

    Free oscillations

    nSl
    Spheroidal mode (related to mantle Rayleigh waves) of angular order l and overtone degree n (number of radial nodal surfaces).
    nTl
    Torsional mode (related to mantle Love waves) of angular order l and overtone degree n (number of radial nodal surfaces).

    Onsets

    i
    impetus or sharp onset (e.g., iP, iPKP, etc.)
    e
    emersio or gentle onset (e.g., eS, ePP, etc.)

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    Last modified: 9/9/97
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