Heterogeneities of short-period S-wave attenuation field in lithosphere of the Himalaya, Indian Plate and South Tibet and their relation to seismicity

Yu.F. Kopnichev¹, I.N. Sokolova²

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

² Branch Institute of Geophysical Research, RSE National Nuclear Center of the Republic of Kazakhstan, Kurchatov, Kazakhstan

Corresponding author: I.N. Sokolova, e-mail: sokolova@kndc.kz

Abstract. We have been studying characteristics of the attenuation field in the lithosphere of the South Asia. Recordings of local earthquakes, obtained by station NIL were analyzed. We considered ratios of maximum amplitudes of S_n and P_n waves within the distance range of ~300–1900 km. A total number of ~200 earthquake seismograms were processed. It was established that as a whole lower attenuation is observed in the uppermost mantle under the Indian Plate (for meridian profile oriented in direction to the source zone of large Bhuj earthquake of 26/01/2001, M_W = 7.7). Considerably higher attenuation corresponds to the regions of the Himalaya and especially South Tibet. It was shown that increased attenuation is observed in the source zone of the recent large Nepal earthquake of 25/04/2015 (M_W = 7.8). At the same time lower and intermediate attenuation takes place in the source zones of large and great interplate events (M_W = 7.0–8.1), occurred in the Himalaya region in 1897–1930. From the other hand, essentially lowered attenuation corresponds to the source zone of the intraplate Bhuj earthquake. New results agree with earlier obtained data, which testify to mantle fluids concentration below source zones prior to large interplate earthquakes, and also to fluids ascending into the earth’s crust after these events. Zones of high attenuation were picked out in the regions of West Himalaya and central Pakistan, where large earthquakes did not occur for a long time. It is supposed that processes of preparation of large seismic events can proceed there.

Keywords: attenuation, S-waves, uppermost mantle, large earthquakes

About the authors:

KOPNICHEV Yuri Fedorovich – Schmidt Institute of Physics of the Earth, Russian Academy of Sciences. Russia, 123242, Moscow, Bolshaya Gruzinskaya st., 10-1. E-mail: yufk777@mail.ru

SOKOLOVA Inna Nikolayevna – Branch Institute of Geophysical Research, RSE National Nuclear Center of the Republic of Kazakhstan. Kazakhstan, 071100, Kurchatov, Meridian site. E-mail: sokolova@kndc.kz

Cite this article as: Kopnichev Yu.F., Sokolova I.N. Heterogeneities of short-period S-wave attenuation field in lithosphere of the Himalaya, Indian Plate and South Tibet and their relation to seismicity, Voprosy Inzhenernoi Seismologii (Problems of Engineering Seismology). 2021. V. 48, No. 2. P. 47–61. [in Russian]. https://doi.org/10.21455/VIS2021.2-3

English translation of the article will be published in Seismic Instruments, ISSN: 0747-9239 (Print) 1934-7871 (Online), https://link.springer.com/journal/11990