Employees of the Department of Physics of Sea and Terrestrial Waters of the Faculty of Physics, Moscow State University, together with colleagues from the Japan Agency for Marine and Terrestrial Research and Technology (JAMSTEC) and Kagawa University (Japan), discovered and studied in detail the effect of the generation of gravitational waves in the ocean by surface seismic waves running along the bottom. The research results are published in the Journal of Geophysical Research.
Scientists from the Physics Department of Moscow State University discovered a new phenomenon - free gravitational waves excited in the ocean by seismic surface waves. There is no short name for the discovered phenomenon that would correctly reflect its physical essence. In the article, scientists suggest the abbreviation "FGSS waves" (Free Gravity waves excited in the ocean by Seismic Surface waves - free gravitational waves excited in the ocean by seismic surface waves). “We deliberately avoid the possible term“tsunami harbinger”, since the presence or absence of FGSS waves does not allow us to unambiguously judge the approaching catastrophe (tsunami),” says the author of the article, head of the geophysics department, professor of the physics of sea and land waters of Moscow State University, Mikhail Nosov.
The relative position of the epicenters of the March 11, 2011 earthquake and the main aftershock (asterisks) and deep-sea observatories DONET (black triangles). The inset shows the bottom topography in the area of the DONET system. The red squares show the GPS stations used to restore the bottom movement.
However, minor fluctuations in sea level near the coast, due to FGSS waves, in principle, can serve as a kind of natural warning signal of a tsunami. In addition, the seismic waves themselves are such a warning signal. In some cases, FGSS waves are likely to have a significant amplitude and pose a threat to life and property. However, this issue requires special study.
“Based on the analysis of the records obtained by the network of deep-sea observatories DONET during the catastrophic earthquake and tsunami of March 11, 2011 off the coast of Japan, it was established that when Love and Rayleigh waves pass along the ocean floor, free gravitational waves arise in the water layer, the appearance of which is more than an hour ahead of the arrival of tsunami waves,”says Professor Mikhail Nosov.
The effect is reproduced numerically using the CPTM (Combined Potential Tsunami Model) 3D model developed at the Department of Physics of Sea and Land Water. Numerical experiments made it possible to establish that free gravitational waves are excited only by low-frequency components of surface seismic waves and exclusively in areas of steep underwater slopes. At the same time, horizontal seismic movements play a key role in the generation of these waves.