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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