Paper:

# Analysis of Pressure and Acceleration Signals from the 2011 Tohoku Earthquake Observed by the DONET Seafloor Network

## Hiroyuki Matsumoto^{*,†}, Mikhail A. Nosov^{**}, Sergey V. Kolesov^{**}, and Yoshiyuki Kaneda^{*,***}

^{*}Research and Development Center for Earthquake and Tsunami, Japan Agency for Marine-Earth Science and Technology

2-15 Natsushima, Yokosuka, Kanagawa 237-0061, Japan

^{**}Faculty of Physics, M. V. Lomonosov Moscow State University

Leninskie Gory, Moscow 119991, Russia

^{***}Institute of Education, Research and Regional Cooperation for Crisis Management Shikoku, Kagawa University

1-1 Saiwai-cho, Takamatsu, Kagawa 760-8521, Japan

^{†}Corresponding author

Ocean-bottom pressure and acceleration data simultaneously recorded by the DONET seafloor network during the 2011 Tohoku earthquake approximately 800 km from the earthquake epicenter are processed and analyzed. The close location of pressure and acceleration sensors together with the high data-sampling rate enable us to quantitatively examine and interpret pressure variations together with ocean-bottom acceleration for the first time to our knowledge. To interpret observed data, we introduce a set of characteristic frequencies that enable us to identify physical processes responsible for water layer behaviour dependent on the frequency of ocean-bottom oscillations. Explicit formulas are given for calculating all of the characteristic frequencies, which are the basis for introducing nonoverlapping frequency bands, i.e., hydroacoustic waves, forced oscillations, and gravity waves. The physical correctness of such a subdivision is confirmed by the high coherence and nearly zero phase difference between in-situ measured pressure and acceleration variations observed in the forced oscillation frequency band – a band neither hydroacoustic nor gravity waves are generated by ocean-bottom oscillation because the water layer simply follows the ocean bottom, generating forced oscillations. The dominant, long-lasting pressure fluctuations recorded by DONET during the 2011 earthquake are associated with the forced oscillation, or, more precisely, with water and sedimentary layer coupling oscillation. DONET clearly observed the 2011 Tohoku tsunami signal during more than 24 hours following the earthquake. In contrast to DART records, phase dispersion was not manifested in the tsunami signals registered by DONET.

*J. Disaster Res.*, Vol.12, No.1, pp. 163-175, 2017.

- [1] Y. Hayashi, H. Tsushima, K. Hirata, K. Kimura, and K. Maeda, “Tsunami source area of the 2011 off the Pacific coast of Tohoku Earthquake determined from tsunami arrival times at offshore observation stations,” Earth Planets Space, Vol.63, pp. 809-813, 2011.
- [2] T. Ozaki, “Outline of the 2011 off the Pacific coast of Tohoku Earthquake (Mw 9.0) – Tsunami warnings/advisories and observations –,” Earth Plants Space, Vol.63, pp. 827-830, 2011.
- [3] T. Maeda, T. Furumura, S. Sakai, and M. Shinohara, “Significant tsunami observed at ocean-bottom pressure gauges during the 2011 off the Pacific coast of Tohoku Earthquake,” Earth Planets Space, Vol.63, pp. 803-808, 2011.
- [4] T. Maeda, T. Furumura, S. Noguchi, S. Takemura, S. Sakai, M. Shinohara, K. Iwai, and S. J. Lee, “Seismic and tsunami wave propagation of the 2011 off the Pacific Coast of Tohoku earthquake as inferred from the tsunami-coupled finite difference simulation,” Bull. Seism. Soc. Am., Vol.103, pp. 1456-1472, 2013.
- [5] J. E. Kozdon and E. M. Dunham, “Constraining shallow slip and tsunami excitation in megathrust ruptures using seismic and ocean acoustic waves recorded on ocean-bottom sensor networks,” Earth Planet. Sci. Lett., Vol.396, pp. 56-65, 2014.
- [6] K. Satake, Y. Fujii, T. Harada, and Y. Namegaya, “Time and space distribution of coseismic slip of the 2011 Tohoku earthquake as inferred from tsunami waveform data,” Bull. Seism. Soc. Am., Vol.103, pp. 1473-1492, 2013.
- [7] S. L. Soloviev, “The tsunami problem and its importance for Kamchatka and the Kuril Islands,” Collected Papers ‘Tsunami Problem’, Nauka, 1968 (in Russian).
- [8] V. M. Jacques and S. L. Soloviev, “Distant registration of small waves of tsunami type on the shelf of the Kuril Islands,” Doklady Akademii Nauk SSR, Vol.198, No.4, 1971 (in Russian).
- [9] B. D. Dykhan, V. M. Jaque, E. A. Kulikov, S. S. Lappo, V. N. Mitrofanov, A. A. Poplavsky, A. V. Rodionov, A. A. Shishkin, and S. L. Soloviev, “Registration of tsunamis in the open ocean,” Marine Geodesy, Vol.6, No.3-4, pp. 303-310, 1983.
- [10] V. V. Titov, F. I. González, E. N. Bernard, M. C. Eble, H. O. Mofjeld, J. C. Newman, and A. J. Venturato, “Real-time tsunami forecasting: Challenges and solutions,” Nat. Hazards, Vol.35, No.1, pp. 41-58, 2005.
- [11] E. Bernard and C. Meinig, “History and future of deep-ocean tsunami measurements,” Proc. Oceans’ 11 MTS/IEEE, No.6106894, 7, 2011. 2011.
- [12] A. Rudloff, J. Lauterjung, U. Münch, and S. Tinti, “The GITEWS Project (German-Indonesian Tsunami Early Warning System),” Nat. Hazards Earth Syst. Sci., Vol.9, pp. 1381-1882, 2009.
- [13] U. Münch, A. Rudoloff, and J. Lauterjung, “The GITEWS Project: Results, summary and outlook,” Nat. Hazards Earth Syst. Sci., Vol.11, pp. 765-769, 2011.
- [14] R. Thomson, I. Fine, A. Rabinovich, S. Mihály, E. Davis, M. Heesemann, and M. Krassovski, “Observation of the 2009 Samoa tsunami by the NEPTUNE-Canada cabled observatory: Test data for an operational regional tsunami forecast model,” Geophys. Res. Lett., Vol.38, L11701, 2011.
- [15] P. Favali and L. Beranzoli, “EMSO: European multidisciplinary seafloor observatory,” Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment., Vol.602, No.1, pp. 21-27, 2009.
- [16] H. Matsumoto and Y. Kaneda, “Review of recent tsunami observation by offshore cabled observatory,” J. Disaster Res., Vol.4, pp. 489-497, 2009.
- [17] B. W. Levin and M. A. Nosov, “Physics of Tsunamis,” Springer, 2016.
- [18] S. C. Webb, “Broadband seismology and noise under the ocean,” Rev. Geophys., Vol.36, No.1, pp. 105-142, 1998.
- [19] J. H. Filloux, “Tsunami record on the open ocean floor,” Geophys. Res. Lett., Vol.9, pp. 25-28, 1982.
- [20] J. H. Filloux, “Pressure fluctuations on the open-ocean floor off the Gulf of California: Tides, earthquakes, tsunamis,” J. Phys. Oceanogr., Vol.13, pp. 783-796, 1983.
- [21] F. E. M. Lilley, P. J. Mulhearn, J. H. Filloux, N. L. Bindoff, and I. J. Ferguson, “Pressure fluctuation on the open-ocean floor: Mid-Tasman Sea at 38
^{circ}3’S, 162^{circ}38’E, near the Lord Howe Rise,” Aust. J. Mar. Freshwat. Res., Vol.37, pp. 27-37, 1986. - [22] A. B. Rabinovich and M. C. Eble, “Deep-ocean measurements of tsunami waves,” Pure Appl. Geopys., 2015.
- [23] J. A. Hanson and J. R. Bowman, “Dispersive and reflected tsunami signals from the 2004 Indian Ocean tsunami observed on hydrophones and seismic stations,” Geophys. Res. Lett., Vol.32, L17606, 2005.
- [24] E. A. Okal, J. Talandier, and D. Reymond, “Quantification of hydrophone records of the 2004 Sumatra tsunami,” Pure Appl. Geophys., Vol.164, pp. 309-323, 2007.
- [25] J. A. Hanson, C. L. Reasoner, and J. R. Bowman, “High-frequency tsunami signals of the great Indonesian earthquakes of 26 December 2004 and 28 March 2005,” Bull. Seism. Soc. Am., Vol.97, S232-S248, 2007.
- [26] E. A. Okal, “Seismic records of the 2004 Sumatra and other tsunamis: A quantitative study,” Pure Appl. Geophys., Vol.164, pp. 325-353, 2007.
- [27] A. B. Rabinovich, R. E. Thomson, and I. V. Fine, “The 2010 Chilean tsunami off the west coast of Canada and the northwest coast of United States,” Pure Appl. Geopys., Vol.170, pp. 1529-1565, 2013.
- [28] H. Matsumoto and Y. Kaneda, “Some features of bottom pressure records at the 2011 Tohoku earthquake – Interpretation of the far-field DONET data,” Proc. 11th SEGJ Int. Symp., pp. 493-496, 2013.
- [29] H. Momma, N. Fujiwara, R. Iwase, K. Kawaguchi, S. Suzuki, and H. Kinoshita, “Monitoring system for submarine earthquakes and deep sea environment,” Proc. MTS/IEEE OCEANS ’97, Vol.2, pp. 1453-1459, 1997.
- [30] H. Momma, R. Iwase, K. Mitsuzawa, Y. Kaiho, and Y. Fujiwara, “Preliminary results of a three-year continuous observation by a deep seafloor observatory in Sagami Bay, central Japan,” Phys. Earth Planet. Inter., Vol.108, pp. 263-274, 1998.
- [31] K. Hirata, M. Aoyagi, H. Mikada, K. Kawaguchi, Y. Kaiho, R. Iwase, S. Morita, I. Fujisawa, H. Sugioka, K. Mitsuzawa, K. Suyehiro, H. Kinoshita, and N. Fujiwara, “Real-time geophysical measurements on the deep seafloor using submarine cable in the southern Kurile subduction zone,” J. IEEE Ocean. Eng., Vol.27, pp. 170-181, 2002.
- [32] H. Matsumoto, S. Inoue, and T. Ohmachi, “Dynamic response of bottom water pressure due to the 2011 Tohoku earthquake,” J. Disaster Res., Vol.7, pp. 468-475, 2012.
- [33] M. A. Nosov and S. V. Kolesov, “Elastic oscillations of water column in the 2003 Tokachi-oki tsunami source: in-situ measurements and 3-D numerical modelling,” Nat. Hazards Earth Syst. Sci., Vol.7, pp. 243-249, 2007.
- [34] A. Bolshakova, S. Inoue, S. Kolesov, H. Matsumoto, M. Nosov, and T. Ohmachi, “Hydroacoustic effects in the 2003 Tokachi-oki tsunami source,” Russ. J. Earth. Sci., Vol.12, ES2005, 2011.
- [35] Y. Tamura, T. Sato, M. Ooe, and M. Ishiguro, “A procedure for tidal analysis with a Bayesian information criterion,” Geophys. J. Int., Vol.104, pp. 507-516, 1991.
- [36] E. A. Okal, P. J. Alasset, O. Hyvernaud, and F. Shinndelé, “The deficient T waves of tsunami earthquakes,” Goephys. J. Int., Vol.152, pp. 416-432, 2003.
- [37] S. Yun and W. S. Lee, “Hydroacoustic observation on the 2011 Tohoku earthquake,” Jigu-Mulli-wa-Mulli-Tamsa, Vol.16, No.4, pp. 234-239, 2013.
- [38] H. O. Mofjeld, P. M. Whitmore, M. C. Eble, F. I. González, and J. C. Newman, “Seismic-wave contributions to bottom pressure fluctuations in the North Pacific – Implications for the DART tsunami array,” Proc. Int. Tsunami Symp., pp. 633-641, 2001.
- [39] M. A. Nosov, K. A. Sementsov, S. V. Kolesov, H. Matsumoto, and B. W. Levin, “Recording of gravity waves formed in the ocean by surface seismic waves during the earthquake of March 11, 2011, off the coast of Japan,” Doklady Earth Sciences, Vol.461, No.2, pp. 408-413, 2015.
- [40] H. Lacombe, “Cours d’océanographie physique: Théories de la circulation générale,” Houles et vagues, Gauthier-Villars, 1965.
- [41] E. Eyov, A. Klar, U. Kadri, and M. Stiassnie, “Progressive waves in a compressible-ocean with an elastic bottom,” Wave Motion, Vol.50, pp. 929-939, 2013.
- [42] I. Tolstoy and C. S. Clay, “Ocean acoustics: Theory and experiment in underwater sound,” 2nd ed., American Institute of Physics, 1987.
- [43] F. Ardhuin, T. Lavanant, M. Obrebski, L. Marié, J. Y. Royer, J. F. d’Eu, B. M. Howe, R. Lukas, and J. Aucan, “A numerical model for ocean ultra-low frequency noise: Wave-generated acoustic-gravity and Rayleigh modes,” J. Acoust. Soc. Am., Vol.134, No.4, pp. 3242-3259, 2013.
- [44] M. A. Nosov, S. V. Kolesov, A. V. Ostroukhova, A. B. Alekseev, and B. W. Levin, “Elastic oscillations of the water layer in a tsunami source,” Doklady Earth Sciences, Vol.404, No.7, pp. 1097-1100, 2005.
- [45] M. A. Nosov, “Generation of tsunami by oscillations of a sea floor section,” Moscow Univ. Phys. Bull., Vol.47, No.1, pp. 110-112, 1992.
- [46] M. A. Nosov, “Tsunami generation in compressible ocean,” Physics and Chemistry of the Earth, Part B: Hydrology, Oceans and Atmosphere, Vol.24, No.5, pp. 437-441, 1999.
- [47] M. A. Nosov, “On the tsunami generation in the compressible ocean by vertical bottom displacements,” Izvestiya, Atmos. Ocean. Phys., Vol.36, No.5, pp. 718-726, 2000.
- [48] M. A. Nosov and S. V. Kolesov, “Optimal initial conditions for simulation of seismotectonic tsunamis,” Pure Appl. Geophys., Vol.168, pp. 1223-1237, 2011.