The low-frequency (4–40 Hz) acoustic waves generated by undersea earthquakes are of great importance to monitor the low-level seismic activity associated with seafloor spreading ridges. To better understand the near-source interaction of seismic waves with the seafloor and the resulting generation of low-frequency acoustic waves, the wave propagation in a solid medium (the Earth's crust) and in the overlaying fluid medium (the ocean) were jointly simulated using a three-dimensional (3D) spectral finite-element code (SPECFEM3D). Due to numerical limitations of 3D simulations, the focus was on simple model configurations with a 1 Hz source located below a Gaussian seamount or ridge. The simulated acoustic waves (0–2.5 Hz) propagate as Rayleigh modes and are affected by modal dispersion; their horizontal speed increases away from the source and reaches the sound speed about 140 km away. The amplitude of the generated acoustic waves is affected by the shape of the seafloor topography above the seismic source, as well as their travel times to hydrophones. Consequently, localization of the acoustic sources by trilateration from arrival times may be biased by 3D-effects, and thus the seismic/acoustic conversion zone may not match the epicenter.
References
1.
Abramovici
, F.
(1968
). “Diagnostic diagrams and transfer functions for ocean waveguides
,” Bull. Seismol. Soc. Am.
58
(1
), 427
–456
.2.
Ardhuin
, F.
, and Herbers
, T. H. C.
(2013
). “Noise generation in the solid Earth, oceans and atmosphere, from nonlinear interacting surface gravity waves in finite depth
,” J. Fluid Mech.
716
, 316
–348
.3.
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
.4.
Bohnenstiehl
, D.
, Tolstoy
, M.
, Dziak
, R.
, Fox
, C.
, and Smith
, D.
(2002
). “Aftershock sequences in the mid-ocean ridge environment: An analysis using hydroacoustic data
,” Tectonophysics
354
(1-2
):49
–70
.5.
Bottero
, A.
(2018
). “Full-wave numerical simulation of T-waves and of moving acoustic sources
,” Ph.D. thesis, Université Aix Marseille, available at https://tel.archives-ouvertes.fr/tel-01893011 (Last viewed 9/9/2019).6.
Bottero
, A.
, Cristini
, P.
, Komatitsch
, D.
, and Asch
M.
(2016
). “An axisymmetric time-domain spectral-element method for full-wave simulations: Application to ocean acoustics
,” J. Acoust. Soc. Am.
140
(5
), 3520
–3530
.7.
Chapman
, N. R.
, and Marrett
, R.
(2006
). “The directionality of acoustic T-phase signals from small magnitude submarine earthquakes
,” J. Acoust. Soc. Am.
119
(6
), 3669
–3675
.8.
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
), 229
–235
.9.
de Groot-Hedlin
, C. D.
, and Orcutt
, J. A.
(1999
). “Synthesis of earthquake-generated T-waves
,” Geophys. Res. Lett.
26
(9
), 1227
–1230
, .10.
Fox
, C. G.
, Matsumoto
, H.
, and Lau
, T.-K. A.
(2001
). “Monitoring Pacific Ocean seismicity from an autonomous hydrophone array
,” J. Geophys. Res.: Solid Earth
106
(B3
), 4183
–4206
, .11.
Geuzaine
, C.
, and Remacle
, J.-F.
(2009
). “Gmsh: A 3-D finite element mesh generator with built-in pre- and post-processing facilities
,” Int. J. Numer. Meth. Eng.
79
(11
), 1309
–1331
.12.
Giusti
, M.
, Perrot
, J.
, Dziak
, R. P.
, Sukhovich
, A.
, and Maia
, M.
(2018
). “The August 2010 earthquake swarm at North FAMOUSFAMOUS segments, Mid-Atlantic Ridge: Geophysical evidence of dike intrusion
,” Geophys. J. Int.
215
(1
), 181
–195
.13.
Jamet
, G.
(2014
). “Modélisation d'ondes sismo-acoustiques par la méthode des éléments spectraux. Application à un séisme dans l'Atlantique Nord” (“Modeling of sismo-acoustic waves by a spectral element method. Application to an earthquake in the North Atlantic”)
, Ph.D. thesis, Université de Bretagne Occidentale, Brest, available in French at https://tel.archives-ouvertes.fr/tel-01091245 (Last viewed 9/9/2019).14.
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
.15.
Jensen
, F. B.
, Kuperman
, W. A.
, Porter
, M. B.
, and Schmidt
, H.
(2011
). Computational Ocean Acoustics
, 2nd ed., in Modern Acoustics and Signal Processing (Springer
, New York
).16.
Johnson
, R. H.
, and Norris
, R. A.
(1968
). “T-phase radiators in the western Aleutians
,” Bull. Seismol. Soc. Am.
58
(1
), 1
–10
.17.
Johnson
, R. H.
, Norris
, R. A.
, and Duennebier
, F. K.
(1968
). “Abyssally Generated T Phases
,” in The Crust and Upper Mantle of the Pacific Area, Geophys. Monogr. Series
, edited by L.
Knopoff
, C. L.
Drake
, and P. J.
Hart
(American Geophysical Union
, Washington, D.C
.) Vol. 12, pp. 70
–78
.18.
Lecoulant
, J.
, Guennou
, C.
, Guillon
, L.
, and Royer
, J.-Y.
(2018
). “Modélisation 3D des ondes acoustiques (ondes T) générées par les séismes sous-marins” [“3D modeling of acoustic waves (T waves) generated by submarine earthquakes”]
, in Actes du 14e Congrès Français d'Acoustique (Proceedings of the 14th French Congress of Acoustics) (Le Havre, France), pp. 339
–343
, available in French at https://www.conforg.fr/cfa2018/output_directory2/data/articles/000136.pdf (Last viewed 9/19/2019).19.
Magnoni
, F.
, Casarotti
, E.
, Michelini
, A.
, Piersanti
, A.
, Komatitsch
, D.
, Peter
, D.
, and Tromp
, J.
(2014
). “Spectral-element simulations of seismic waves generated by the 2009 L'Aquila earthquake
,” Bull. Seismol. Soc. Am.
104
(1
), 73
–94
.20.
Okal
, E. A.
(2008
). “The generation of T waves by earthquakes
,” in Advanced Geophysics
(Elsevier
, Amsterdam
), Vol. 49
, pp. 1
–65
.21.
Peter
, D.
, Komatitsch
, D.
, Luo
, Y.
, Martin
, R.
, Le Goff
, N.
, Casarotti
, E.
, Le Loher
, P.
, Magnoni
, F.
, Liu
, Q.
, Blitz
, C.
, Nissen-Meyer
, T.
, Basini
, P.
, and Tromp
, J.
(2011
). “Forward and adjoint simulations of seismic wave propagation on fully unstructured hexahedral meshes: SPECFEM3d Version Sesame
,” Geophys. J. Int.
186
(2
), 721
––739
.22.
Royer
, J.-Y.
, Chateau
, R.
, Dziak
, R.
, and Bohnenstiehl
, D.
(2015
). “Seafloor seismicity, Antarctic ice-sounds, cetacean vocalizations and long-term ambient sound in the Indian Ocean basin
,” Geophys. J. Int.
202
(2
), 748
–762
.23.
Searle
, R.
(2013
). Mid-Ocean Ridges
(Cambridge University Press
, Cambridge, UK)
.24.
Shearer
, P. M.
(2009
). Introduction to Seismology
, 2nd ed. (Cambridge University Press
, Cambridge, UK)
.25.
Smith
, D. K.
, Escartin
, J.
, Cannat
, M.
, Tolstoy
, M.
, Fox
, C. G.
, Bohnenstiehl
, D. R.
, and Bazin
, S.
(2003
). “Spatial and temporal distribution of seismicity along the northern Mid-Atlantic Ridge (15°–35°N)
,” J. Geophys. Res.: Solid Earth
108
(B3
), 2167
–2188
, .26.
Tarantola
, A.
(2005
). Inverse Problem Theory and Methods for Model Parameter Estimation
(Society for Industrial and Applied Mathematics
, Philadelphia, PA
).27.
Tromp
, J.
, Komatitsch
, D.
, and Qinya
, L.
(2008
). “Spectral-element and adjoint methods in seismology
,” Commun. Comput. Phys.
3
(1
), 1
–32
.28.
Tsang-Hin-Sun
, E.
, Royer
, J.-Y.
, and Perrot
, J.
(2016
). “Seismicity and active accretion processes at the ultraslow-spreading Southwest and intermediate-spreading Southeast Indian ridges from hydroacoustic data
,” Geophys. J. Int.
206
(2
), 1232
–1245
.29.
Viktorov
, I. A.
(1967
). Rayleigh and Lamb Waves Physical Theory and Applications
(Springer
, New York
).30.
Xie
, Z.
, Matzen
, R.
, Cristini
, P.
, D.
Komatitsch
, 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
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