EARTH’S FREE OSCILLATIONS EXCITED BY THE 2013
SEA OF OKHOTSK EARTHQUAKE

V.K. Milyukov1, 2, M.P. Vinogradov1, A.P. Mironov1, A.V. Myasnikov1

1 Sternberg Astronomical Institute, Lomonosov Moscow State University, Moscow, Russia

2 Vladikavkaz Scientific Center of RAS, Vladikavkaz, Republic of North Ossetia – Alania, Russia

Abstract. Based on the deformation data measured by the Baksan laser interferometer-strainmeter, the analysis of the Earth’s Free Oscillations (EFO) excited by the deep-focus Sea of Okhotsk earthquake on May 24, 2013, the largest recorded deep-focus earthquake, has been performed. The periods of
50 fundamental modes of EFO in the range 1.2–5.0 mHz with an error of 3–12 μHz are determined.  
A comparison of the EFO spectra for the deep-focus Okhotomorsky earthquake on May 24, 2013 and the Simushir crust earthquake on November 15, 2006 revealed a number of features of excitation of EFO by the deep-focus earthquake. It is established that for the deep-focus earthquake, more overtones (both spheroidal and toroidal) are observed. The amplitude values ​​of the EFO modes observed from the deep-focus earthquake are greater than from the crustal earthquake, with a smaller observed deformation. The presence of interacting spheroidal and toroidal modes close in frequency (the coupling effect) is revealed. A method is proposed that makes it possible to obtain an estimate of the EFO modes over the beat period between close frequencies, which are not observed explicitly in the spectrum. The application of the method to the deformation data made it possible to find the frequencies of nine pairs of close EFO modes.

Keywords: Earth’s free oscillations, deep-focus earthquake, deformation.

About the authors

MILYUKOV Vadim K. – Dr.  Sci. (Phys.-Math.), head of laboratory, Sternberg Astronomical Institute, Lomonosov Moscow State University. Moscow, Russia; senior researcher, Vladikavkaz Scientific Center of RAS, Vladikavkaz, Republic of North Ossetia – Alania, Russia.
Tel.: +7 (495) 939-16-34. E-mail: vmilyukov@yandex.ru

VINOGRADOV Mikhail P. – leading engineer, Sternberg Astronomical Institute, Lomonosov Moscow State University. Moscow, Russia. Tel.: +7 (495) 939-16-34. E-mail: rospak@inbox.ru

MIRONOV Alexey P. – science researcher, Sternberg Astronomical Institute, Lomonosov Moscow State University. Moscow, Russia. Tel.: +7 (495) 939-16-34. E-mail: almir@physics.msu.ru

MYASNIKOV Andrey V. – Cand. Sci. (Phys. and Math.), science researcher, Sternberg Astronomical Institute, Lomonosov Moscow State University. Moscow, Russia. Tel.: +7 (495) 939-16-34.
E-mail: andrey0405@mail.ru