STANDING WAVES IN EPICENTRAL AREA OF EARTHQUAKE

F.F.Aptikaev, O.O.Erteleva

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

Corresponding author: F.F. Aptikaev, e-mail: felix@ifz.ru

Abstract. Often a sharp increase or decrease in the level of seismic waves cannot be explained by existing methods of seismic microzonning. Especially the amplification of the amplitude on soft ground, when intensity is 8–9, does not occur, rather the contrary. Attenuation of seismic waves for large amplitudes isn’t determined by the properties of the medium, but the vibration level. The decrement of the absorption sharply increases, and the resonant properties of soils blunted until the complete disappearance. Moreover, the areas is located above the source area, where not only an absorption, but also the release of energy. The article discusses three processes that can explain the abnormal variation of the amplitudes of seismic waves. First, with distance from the fault, the amplitude may increase, because the gap may occur not in place of the maximum deformation but the minimum strength of the medium, i.e. in the previously formed fault. However, this model does not agree with the fact that the zones of abnormal amplitudes are often located symmetrically with respect to the fault. The second reason for the increasing amplitude with distance from the fault due to the fact that in the fault surface energy, of course, cannot be. The rift only allows the release of stored energy of deformation in the surrounding environment. Therefore, the energy of the seismic waves during the propagation from the fault would increase as long as the elements of the environment will allocate more energy than to absorb. This model is confirmed by empirical data. The scaling of the amplitudes of the accelerations during the earthquakes with different magnitudes is well executed shift along the axis of distances, not along the axis of the amplitudes, as is commonly believed. It is shown by many researchers that the maximum level of acceleration in the source area does not depend on the magnitude but depends on the type of movement along the fault. It is empirically shown that the levels of acceleration for intensities 9–11 are the same. Seismic intensity above 9 isn’t determined by the amplitude of the acceleration but of residual deformation, i.e., changes in the topography. The phenomenon of alternation of zones of gain and weakening of amplitudes under identical soil conditions observed in epicentral areas of earthquakes is not explained also by two described processes. Authors offer for discussion the idea explaining the specified phenomena - origin of standing waves in focal area. Data on appearance of the abnormal variations of amplitudes which can be explained with the theory of standing waves are provided in article. At the same time zones of the abnormal increase and reduction of amplitudes can be interpreted as zones of nodes and antinodes of standing waves. Empirical equations for distances at which zones of nodes and antinodes can appear are offered.

Keywords: earthquake magnitude, standing waves, nodes, antinodes, tectonic faults, ground conditions

About the authors

APTIKAEV Felix Fuadovich - Doctor of Physics and Mathematics, Professor, Chief Researcher. Schmidt Institute of Physics of the Earth of the Russian Academy of Sciences. 123242, Moscow, D-242, ul. Bolshaya Gruzinskaya, 10. Tel .: (499) 254-24-85. E-mail: felix@ifz.ru

ERTELEVA Olga Olegovna - Candidate of Physical and Mathematical Sciences, Leading Researcher, Schmidt Institute of Physics of the Earth of the Russian Academy of Sciences. 123242, Moscow, D-242, ul. Bolshaya Gruzinskaya, 10. Tel .: (499) 254-24-85. E-mail: ertel@ifz.ru

Cite this article as: Aptikaev F.F., Erteleva O.O. Standing waves in epicentral area of earthquake, Voprosy Inzhenernoi Seismologii (Problems of Engineering Seismology), 2018, Vol. 45, No. 3, pp. 45–56. [in Russian]. DOI: 10.21455/VIS2018.3-4

English translation of the article will be published in Seismic Instruments, ISSN: 0747-9239 (Print) 1934-7871 (Online), https://link.springer.com/journal/11990), 2019, Volume 55, Issue 3.