CHARACTERISTICS OF SHORT-PERIOD S-WAVE ATTENUATION FIELD IN THE RUPTURE ZONE OF THE GREAT TOHOKU EARTHQUAKE OF 11/03/2011 (Mw 9.0)

1 Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, Moscow, Russia

2 Institute of Geophysical Research of Ministry of Energy of Republic Kazakhstan, Almaty, Kazakhstan

* e-mail: yufk777@mail.ru

Abstract. We have been considering characteristics of short-period S-wave attenuation field in the rupture zone of the great Tohoku earthquake of 11.03.2011. Recordings of shallow local earthquakes by station MAJO at distances of ~250–700 km were processed. We used a method based on an analysis of maximum amplitudes in Sn and Pn waves (parameter Sn/Pn). The rupture zone was divided into 4 areas bounded by coordinates of 36°–37°, 37°–38°, 38°–39° и 39°–40°18ʹ N; 140°30ʹ–145° E. It was established that sections of rapid Sn/Pn values decay are picked out at small epicentral distances in all the areas, which follow by sections of their spasmodic growth. One more section of rapid Sn/Pn parameter decay is picked out in all the areas at relatively big distances. It is supposed that the first sections of rapid Sn/Pn values decay are connected with gradual sinking of S-wave rays into the mantle wedge. In this case minimal parameter values correspond to rays partly going along the wedge foot. Such an effect can be explained by the biggest content of deep-seated fluids ascending due to oceanic crust dehydration. The sections of sharp Sn/Pn values increase most probably correspond to rays propagation within the upper part of the sinking plate, which has very weak attenuation. The second sections of the rapid Sn/Pn values decay probably correspond to the ray penetration into waveguide within the plate, which has been formed as a result of mantle rocks dehydration. The mean values Sn/Pn(Δ) in the four areas are essentially lower than in the rupture zone of the great Maule earthquake of 27.02.2010 (Chile, Mw 8.8). This effect agrees with an earlier supposition on bigger fluid content within subduction zones at the west of Pacific in comparison with the east of it. Besides that, this allows us to explain peculiarities of the aftershock processes in the two enormous regions of the Pacific ring.

Keywords: S-waves, attenuation, the Great Tohoku earthquake, deep-seated fluids.

Cite this article as: Kopnichev Yu.F., Sokolova I.N. Characteristics of short-period S-wave attenuation field in the rupture zone of the Great Tohoku earthquake of 11/03/2011 (Mw 9.0), Geofizicheskie Protsessy i Biosfera (Geophysical Processes and Biosphere), 2019, vol. 18, no. 2, pp. 16–27 (in Russian). https://doi.org/10.21455/gpb2019.2-2

English version: Izvestiya, Atmospheric and Oceanic Physics, 2019, vol. 55, iss. 8. ISSN: 0001-4338 (Print), 1555-628X (Online). https://link.springer.com/journal/volumesAndIssues/11485

About the authors

KOPNICHEV Yuri F. – Dr. Sci. (Phys. and Math.), professor, chief researcher, Schmidt Institute of Physics of the Earth, Russian Academy of Sciences. Russia, 123242, Moscow, Bolshaya Gruzinskaya st., 10-1. Tel.: +7 (7272) 956-350. E-mail: yufk777@mail.ru

SOKOLOVA Inna N. – Dr. Sci. (Phys. and Math.), leading researcher, Institute of Geophysical Research of Ministry of Energy of Republic Kazakhstan. Kazakhstan, 050020, Almaty, Chaykinoy st., 4. Tel.: +7 (7272) 631-330. E-mail: sokolova.inessa@mail.ru