This paper discusses the nature of the low-frequency seismo-acoustic waves generated by submarine earthquakes in the ocean. In a finite-depth homogeneous ocean over a semi-infinite solid crust, the derivation of the acoustic equations shows that waves propagate as modes. The waves propagating with the speed of sound in water (T waves) are preceded by waves with frequencies below the Airy phase. Furthermore, the group speeds of these modes are sensitive to the environmental setting. As a test, we applied the spectral finite-element code SPECFEM2D in a simplified configuration with an ocean layer overlaying a solid crust, and a seismic source below a Gaussian seamount surrounded by a flat seafloor. The simulations confirm that the generated T waves and their precursors follow the theoretical dispersion curves. A more realistic environment with a seismically-layered crust and a sound-speed profile in the ocean is then used to predict the expected acoustic modes. Although noisy, recordings by ocean bottom seismometers from the southwest Indian Ocean show T waves preceded by ultra-low frequency waves, which display two modes comparable to the theoretical ones. They are in good agreement for mode 1, whereas, for mode 0, a slight offset in frequency has yet to be explained.
References
1.
Ardhuin
, F.
, Lavanant
, T.
, Obrebski
, M.
, Mari
, L.
, Royer
, J.-Y.
, d'Eu
, J.-F.
, Howe
, B. M.
, Lukas
, R.
, and Aucan
, J.
(2013
). “A numerical model for ocean ultra-low frequency noise: Wave-generated acoustic-gravity and Rayleigh modes
,” J. Acoust. Soc. Am.
134
(4
), 3242
–3259
.2.
Ball
, J. S.
, Godin
, O. A.
, Evers
, L. G.
, and Lv
, C.
(2016
). “Long-range correlations of microseism-band pressure fluctuations in the ocean
,” Geophys. J. Int.
206
(2
), 825
–834
.3.
Barruol
, G.
, and Sigloch
, K.
(2013
). “Investigating La Réunion hot spot from crust to core
,” Eos. Trans. AGU.
94
(23
), 205
–207
.4.
Bassin
, C.
, Laske
, G.
, and Masters
, G.
(2000
). “The current limits of resolution for surface wave tomography in North America
,” EOS Trans. Am. Geophys. Union
81
, F897
.5.
Biot
, M. A.
(1952
). “The interaction of Rayleigh and Stoneley waves in the ocean bottom
,” Bull. Seism. Soc. Am
42
(1
), 81
–93
.6.
Bottero
, A.
(2018
). “Full-wave numerical simulation of t-waves and of moving acoustic source
,” Ph.D. thesis, Université Aix-Marseille
, Marseille, France
.7.
Butler
, R.
, and Lomnitz
, C.
(2002
). “Coupled seismoacoustic modes on the seafloor
,” Geophys. Res. Lett.
29
(10
), 57-51
–57-4
, .8.
Chen
, C. W.
, Huang
, C. F.
, Lin
, C. W.
, and Kuo
, B. Y.
(2017
). “Hydroacoustic ray theory-based modeling of T wave propagation in the deep ocean basin offshore eastern Taiwan
,” Geophys. Res. Lett.
44
(10
), 4799
–4805
, .9.
Cristini
, P.
, and Komatitsch
, D.
(2012
). “Some illustrative examples of the use of a spectral-element method in ocean acoustics
,” J. Acoust. Soc. Am.
131
(3
), EL229
–EL235
.10.
de Groot-Hedlin
, C. D.
, and Orcutt
, J. A.
(1999
). “Synthesis of earthquake-generated T-waves
,” Geophys. Res. Lett.
26
(9
), 1227
–1230
, .11.
de Groot-Hedlin
, C. D.
, and Orcutt
, J. A.
(2001
). “Excitation of T-phases by a seafloor scattering
,” J. Acoust. Soc. Am.
109
(5
), 1944
–1954
.12.
Divins
, D. L.
(2003
). Total Sediment Thickness of the World's Oceans & Marginal Seas
(NOAA National Geophysical Data Center
, Boulder, CO
).13.
D'Spain
, G. L.
, Berger
, L. P.
, Kuperman
, W. A.
, Stevens
, J. L.
, and Baker
, G. E.
(2001
). “Normal mode composition of earthquake T phases
,” Pure Appl. Geophys.
28
(13
), 2537
–2540
.14.
Dushaw
, B.
(2011
). “Worldwide sound speed, temperature, salinity, and buoyancy from the NOAA World Ocean Atlas
,” https://staff.washington.edu/dushaw/WOA/ (Last viewed March 3, 2022).15.
Dziak
, R. P.
(2001
). “Empirical relationship of T-waves energy and fault parameters of northeast Pacific Ocean earthquakes
,” Geophys. Res. Lett.
28
(13
), 2537
–2540
, .17.
Ewing
, M.
, Jardetzky
, W. S.
, and Press
, F.
(1957
). Elastic Waves in Layer Media
(McGraw-Hill
, New York
).16.
Ewing
, M.
, Tolstoy
, I.
, and Press
, F.
(1950
). “Propose use of the T phase in tsunami warning systems
,” Bull. Seism. Soc. Am.
40
(1
), 53
–58
.18.
Fox
, C. G.
, Dziak
, R. P.
, Matsumoto
, H.
, and Schreiner
, A. E.
(1994
). “Potential for monitoring low-level seismicity on the Juan de Fuca Ridge using military hydrophone arrays
,” Mar. Tech. Soc. J.
27
(4
), 22
–30
.19.
Fox
, C. G.
, Matsumoto
, H.
, and Lau
, T.-K. A.
(2001
). “Monitoring Pacific Ocean seismicity from an autonomous hydrophone array
,” J. Geophys. Res.
106
(B3
), 4183
–4206
, .20.
Franck
, S. D.
, Collis
, J. M.
, and Odom
, R. I.
(2015
). “Elastic parabolic equation solutions for oceanic T-waves generation and propagation from deep seismic sources
,” J. Acoust. Soc. Am.
137
, 3534
–3543
.27.
21.
Jamet
, G.
, Guennou
, C.
, Guillon
, L.
, Mazoyer
, C.
, and Royer
, J.-Y.
(2013
). “T-wave generation and propagation: A comparison between data and spectral element modeling
,” J. Acoust. Soc. Am.
134
(4
), 3376
–3385
.23.
Johnson
, R. H.
(1966
). “Routine location of T-phase sources in the Pacific
,” Bull. Seism. Soc. Am.
56
(1
), 109
–118
.24.
Johnson
, R. H.
, Norris
, R. A.
, and Dunnebier
, F. K.
(1968
). “Abyssal generated T phase
,” in Crust Upper Mantle Pacific Area
(AGU
, Washington, DC
), Vol. 12
.22.
Johnson
, R. H.
, Northrop
, J.
, and Eppley
, R.
(1963
). “Source of Pacific T waves
,” J. Geophys. Res.
68
(14
), 4251
–4260
, .25.
Lecoulant
, J.
, Guennou
, C.
, Guillon
, L.
, and Royer
, J.-Y.
(2019
). “Three-dimensional-modeling of earthquake generated acoustic waves in the ocean in simplified configurations
,” J. Acoust. Soc. Am.
146
(3
), 2113
–2123
.26.
Milne
, A. R.
(1959
). “Comparison of spectra of an earthquake T phase with similar signals from nuclear explosions
,” Bull. Seism. Soc. Am.
49
(4
), 317
–329
.27.
Network YV
(2011
). “Résif: Network YV (2011)
,” (Last viewed May 10, 2022).27.
NOAA
(2015
). “WOA09: NOAA World Ocean Atlas 2009
,” https://www.nodc.noaa.gov/OC5/WOA09/pr_woa09.html (Last viewed March 3, 2022).28.
Officer
, C. B.
(1958
). Introduction to the Theory of Sound Transmission, with Application to the Ocean
(McGraw-Hill
, New York
).29.
Oliveira
, T.
, and Lin
, Y.-T.
(2019
). “Three-dimensional global scale underwater sound modeling: The T-phase wave propagation of a Southern Mid-Atlantic Ridge earthquake
,” J. Acoust. Soc. Am.
146
(3
), 2124
–2135
.30.
Park
, M.
, Odom
, R. I.
, and Soukip
, D. J.
(2001
). “Modal scattering: A key to understanding oceanic T-waves
,” Geophys. Res. Lett.
28
(17
), 3401
–3404
.31.
Pekeris
, C. L.
(1948
). “Theory of propagation of explosive sound in shallow water
,” Geol. Soc. Am. Mem.
27
(2
), 117
.32.
Piserchia
, P.-F.
, Virieux
, J.
, Rodrigues
, D.
, Gaffet
, S.
, and Talandier
, J.
(1998
). “Hybrid numerical modelling of T-wave propagation: Application to the Midplate experiment
,” Geophys. J. Int.
133
(3
), 789
–800
.33.
Porter
, M. B.
(1991
). The Kraken Normal Mode Program, User's Manual
(SACLANT Undersa Research Centre
, La Spezia, Italy
).34.
Press
, F.
, Ewing
, M.
, and Tolstoy
, I.
(1950
). “The Airy phase of a shallow-focus submarine earthquake
,” Bull. Seism. Soc. Am.
40
(2
), 111
–148
.35.
Schreiner
, A. E.
, Fox
, C. G.
, and Dziak
, R. P.
(1995
). “Spectra and magnitudes of T-waves from the 1993 earthquake swarm on the Juan de Fuca Ridge
,” Geophys. Res. Lett.
22
(2
), 139
–142
, https://doi.o10.1029/94GL01912.36.
37.
Stähler
, S. C.
, Silgoch
, K.
, Hosseini
, K.
, Crawford
, W. C.
, Barruol
, G.
, Schmidt-Aursch
, M. C.
, Tsekhmistrenko
, M.
, Scholz
, J.-P.
, Mazzullo
, A.
, and Deen
, M.
(2016
). “Performance report of the RHUM-RUM ocean bottom seismometer network around La Réunion, western Indian Ocean
,” Adv. Geosci.
41
, 43
–63
.38.
Stevens
, J. L.
, Hanson
, J.
, Nielsen
, P.
, Zampolli
, M.
, Bras
, R. L.
, Haralabus
, G.
, and Day
, S. M.
(2020
). “Calculation of hydroacoustic propagation and conversion to seismic phases at T-stations
,” Pure Appl. Geophys.
178
, 2579
–2609
.39.
Stoneley
, R.
(1926
). “The effect of the ocean on Rayleigh waves
,” Mon. Not. R. Astron. Soc. Geophys.
1
(7
), 349
–356
.40.
Talandier
, J.
, and Okal
, E. A.
(1998
). “On the mechanism of conversion of seismic waves to and from T waves in the vicinity of island shores
,” Bull. Seism. Soc. Am.
88
(2
), 621
–632
.41.
Tolstoy
, L.
, and Ewing
, W. M.
(1950
). “The T phase of shallow-focus earthquakes
,” Bull. Seism. Soc. Am.
40
(2
), 25
–52
.42.
Tromp
, J.
, Komatitsch
, D.
, and Qinya
, L.
(2008
). “Spectral-element and adjoint methods in seismology
,” Commun. Comput. Phys.
3
(1
), 1
–32
.43.
Viktorov
, I. A.
(1967
). Rayleigh and Lamb Waves Physical Theory and Applications
(Springer
, New York
).44.
Vinh
, P. C.
(2013
). “Scholte-wave velocity formulae
,” Wave Motion
50
(2
), 180
–190
.45.
Xie
, Z.
, Matzen
, R.
, Cristini
, P.
, Komatitsch
, D.
, and Martin
, R.
(2016
). “A perfectly matched layer for fluid-solid problems: Application to ocean-acoustics simulations with solid ocean bottoms
,” J. Acoust. Soc. Am.
140
(1
), 165
–175
.46.
Yang
, Y.
, and Forsyth
, D. W.
(2003
). “Improving epicentral and magnitude estimation of earthquakes from T-phases by considering the excitation function
,” Bull. Seism. Soc. Am.
93
(5
), 2106
–2122
.© 2022 Acoustical Society of America.
2022
Acoustical Society of America
You do not currently have access to this content.
