COMPUTATION OF SEISMOGRAMS AND ATMOSPHERIC OSCILLATIONS BY NORMAL-MODE SUMMATION FOR A SPHERICAL EARTH MODEL WITH REALISTIC ATMOSPHERE

We describe a theory to compute seismograms and atmospheric disturbances such as ionospheric oscillations or pressure variations in a realistic spherical earth model with atmosphere. This theory is valid for a source located either in the solid earth or in the atmosphere. Solid earth and atmospheric normal modes are computed for a radiation boundary condition that models the dissipation of acoustic signals in the high atmosphere of the Earth. We show that the coupling between ground and atmosphere occurs at a set of frequencies related to fundamentals and harmonics of atmospheric modes. Spheroidal modes near these frequencies have up to 0.04 per cent of their energy in the atmosphere, and thus may be strongly excited by atmospheric sources. This theory can be used for more accurate modelling of the seismic data from meteoritic events or volcanic eruptions as well as for the analysis of barograms or ionograms recorded after large earthquakes.

[1]  J. Tromp,et al.  Free oscillations of a spherical anelastic earth , 1990 .

[2]  J. Bernard Minster,et al.  GPS detection of ionospheric perturbations following the January 17, 1994, Northridge Earthquake , 1995 .

[3]  V. Ferrari.  Non-radial oscillations of stars in general relativity: a scattering problem , 1992, Philosophical Transactions of the Royal Society of London. Series A: Physical and Engineering Sciences.

[4]  Fukao,et al.  Earth's background free oscillations , 1998, Science.

[5]  Freeman Gilbert,et al.  Coupled free oscillations of an aspherical, dissipative, rotating Earth: Galerkin theory , 1986 .

[6]  P. Lognonné.  Normal modes and seismograms in an anelastic rotating Earth , 1991 .

[7]  B. Mosser,et al.  Excitation of Jovian Seismic Waves by the Shoemaker-Levy 9 Cometary Impact , 1994 .

[8]  F. A. Dahlen,et al.  The Effect of A General Aspherical Perturbation on the Free Oscillations of the Earth , 1978 .

[9]  Don L. Anderson,et al.  Velocity dispersion due to anelasticity; implications for seismology and mantle composition , 1976 .

[10]  A. Furumoto,et al.  Acoustic Coupling into the Ionosphere from Seismic Waves of the Earthquake at Kurile Islands on August 11, 1969 , 1970, Nature.

[11]  M. Sauvage,et al.  Impact Seismology: A Search for Primary Pressure Waves Following Impacts A and H , 1996 .

[12]  H. Kanamori,et al.  Atmospheric gravity waves from the impact of comet Shoemaker‐Levy 9 with Jupiter , 1994 .

[13]  B. S. Garbow,et al.  Matrix Eigensystem Routines — EISPACK Guide , 1974, Lecture Notes in Computer Science.

[14]  A. Deschamps,et al.  High-frequency seismo-electromagnetic effects , 1993 .

[15]  A. Furumoto,et al.  Continuous, traveling coupling between seismic waves and the ionosphere evident in May 1968 Japan earthquake data , 1969 .

[16]  T. Tanimoto.  Excitation of normal modes by atmospheric turbulence: source of long-period seismic noise , 1999 .

[17]  Ari Ben-Menahem,et al.  Source parameters of the siberian explosion of June 30, 1908, from analysis and synthesis of seismic signals at four stations , 1975 .

[18]  B. Romanowicz,et al.  Modelling of coupled normal modes of the Earth: the spectral method , 1990 .

[19]  H. Kanamori,et al.  Harmonic excitation of mantle Rayleigh waves by the 1991 eruption of Mount Pinatubo, Philippines , 1992 .

[20]  T. Georges.  Infrasound from convective storms: Examining the evidence , 1973 .

[21]  W. Zürn,et al.  Bichromatic excitation of long‐period Rayleigh and air waves by the Mount Pinatubo and El Chichon volcanic eruptions , 1992 .

[22]  H. Kanamori.  Excitation of Jovian normal modes by an impact source , 1993 .

[23]  Brian T. Smith,et al.  Matrix Eigensystem Routines — EISPACK Guide , 1974, Lecture Notes in Computer Science.

[24]  H. Kanamori,et al.  Excitation of atmospheric oscillations by volcanic eruptions , 1994 .

[25]  George E. Backus,et al.  Moment Tensors and other Phenomenological Descriptions of Seismic Sources—I. Continuous Displacements , 1976 .

[26]  T. Dowling,et al.  HST imaging of atmospheric phenomena created by the impact of comet Shoemaker-Levy 9 , 1995, Science.

[27]  G. Cevolani.  The explosion of the bolide over Lugo di Romagna (Italy) on 19 January 1993 , 1994 .

[28]  Naoki Kobayashi,et al.  Earth's continuous oscillations observed on seismically quiet days , 1998 .

[29]  E. Lavely,et al.  The effect of global-scale, steady-state convection and elastic-gravitational asphericities on helioseismic oscillations , 1992, Philosophical Transactions of the Royal Society of London. Series A: Physical and Engineering Sciences.

[30]  D. L. Anderson,et al.  Preliminary reference earth model , 1981 .

[31]  H. Kanamori,et al.  Waves from the collisions of comet Shoemaker–Levy 9 with Jupiter , 1995, Nature.

[32]  H. Takeuchi,et al.  Seismic Surface Waves , 1972 .

[33]  M. Parrot,et al.  Response of the ionosphere to natural and man-made acoustic sources , 1995 .

[34]  Kazunari Nawa,et al.  Incessant excitation of the Earth’s free oscillations , 1998 .