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instability occurs when increasing R reaches unity. A classical pulse-propagatlon problem in geophysics has been used to demonstrate a technique of the differential transform over that of Cagniard (183). Adapth/e prediction has been applled (184) to detect smali seismic events in microseismic background nolse.

WAVES DUE TO EX?LOSION

The seismic waves from large explosion$ (185) have been studied. and source models for underground nuclear exploslons have been reviewed (186). Low-frequency components of the near-field ground motions (187) produced by surface explosions and Rayleigh waves from atmospheric explosions (7) have been discussed. The kinematic and dynamie parameters of transverse waves resulting from explo-sions have been analyzed (188), and the P- and S-wave velocity variations from some explosions (281) have been determined.

The waves generated by explosions have been studied for the crustal structure in the western Kanto district (190). Ground shock propagation in a layered Earth produced by near-surface airburst explosions has been considered (191) using Cagniard elastic propagation theory. Forma! Solutions for ocean bottom disturbances due to underwater explosions have been derh/ed using the Haskell matrix formulation (192). A nonstationary model has been proposed (193. 194) for seismic records of P waves from underground nuclear explosion$ and natural earthquakes.

The teleseismic P-wave travel-time residuals of shal-low eerthquakes and nuclear expłosions (195). the propagation of signals from an underground source through a seismically active zonę (196). and the radiation of waves during an explosion in a porous medium (197) have been studied. Surface-wave observations from underground explosion$ have been attributed to the phenomenon of spali (198). Spec-tral analysis of explosion earthquakes associated with single eruptions of the Asama Volcano in 1973 were considered (199); a model mechanism of a single explosive eruption was described.

H WAVES

Examinatk>n of seismic records due to explosion of an atomie bomb resulted in recognition of a new type of wave called a hydrodynamic wave and tenta-tively labelled H (200. 201). These H waves are surface wave$ and can be seen in unconsolidated sediments (202).

It is possible in certaln circumstances for two Rayleigh waves to propagate over the free surface of a semi-infinite linear viscoelastic solid (203, 204). When two such waves propagate, one is essentially of the elastic type; the other wave is prograde 8t the surface with the axis tilted at an angle to the free surface. The essentlal features of H waves have been described (202J; these waves are probabły Rayleigh waves propagating in a viscoel8$tic medium.

OSCILLATION AND ROTATION 0F THE EARTH WITH SOME MODELS

Normal (205) and toroidal (206) modes of a later-ally heterogeneous body. axisymmetric free oscllla-tions of a fluid-filled spherical Shell (207). and radial oscillations of a uniform gravitating sphere with a materiał boundary (208) have been discussed. A method of spectral decomposition for linear opera-tors. formulated in Dirac's bracket notation. provides excitation formulas for normal modes of infłniteslmal oscillations of a nonrotating Earth (209); the formal-ism has been extended to obtaln corresponding formulas for a rotating Earth.

The ray method has been used (210) to study free oscillations of an incompressible. inviscid, perfectly conducting fluid of constant density contalned in a rotating Shell in the presence of a constant toroidal magnetic field. The excitation of oscillation of an elastic rotating Earth has been examined for the case when internat point sources and external sources of stresses vary with time according to a given law

(211) . The linearized equation of motion for a slightly elliptical rotating Earth has been obtained

(212) ; the variational principle was derived for normal modę oscillations of Earth. A normal modę spectrum of Earth (213) as a generalized 8urgers' body and a normal-mode solutlon for spherical Earth models (7) have been discussed. Equatlonsfor spheroidal (214-216) and radial oscillations of Earth and for a multilayered spherical Earth (218) have been discussed. The effect of modal coupling for torsional eigenvibratlons of an anelastic Earth with oceanie and Continental structures has been examined (219).