Nomenclature of Seismic Phases

Contents

• Near-earthquake phases
• Phases of distant shallow earthquakes
• Phases of deep-focus earthquakes
• Surface waves
• Free oscillations
• Onsets

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.

PK^jP

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.

R_j, G_j (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

_nS_l

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

_nT_l

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.)

Date created: 8/27/97
Last modified: 9/9/97
Copyright © 1997, Global Seismological Services
Maintained by: Eric Bergman
bergman@seismo.com