Modeling of Nonlinear Passing of Acoustic Waves Caused by Underground Fracturing Through the Lithosphere

Details Modeling of Nonlinear Passing of Acoustic Waves Caused by Underground Fracturing Through the Lithosphere Modeling of Nonlinear Passing of Acoustic Waves Caused by Underground Fracturing Through the Lithosphere

Apr 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja.....4504k&link_type=abstract

EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #4504

Physics

Scientific paper

During earthquakes and strong underground explosions, nonlinear propagation of acoustic waves through the lithosphere to the Earth's surface takes place. This occurs due to elastic nonlinearity. The waves are excited by underground sources at the earthquake epicenter. The acoustic waves propagating almost vertically upwards change their spectra. A wide spectrum of the acoustic waves till the radio frequency range caused by fracturing the rock on the surface is observed by means of satellite measurements and radio telescope investigations of meteor showers bombing the Moon. If deep underground fracturing occurs, high frequencies due to the nonlinear interaction transform into higher and lower parts of the spectrum. Higher frequencies are subject to strong dissipation. Extremely low and ultra low frequency elastic waves may reach the Earth's surface and excite a response in seismograms. In the report, the theory of this nonlinear interaction and the results of simulations are presented. The effect is analogous to the nonlinear interaction and a frequency conversion of atmospheric acoustic and acoustic gravity waves so that only ultra low frequency acoustic waves can propagate through the ionosphere. For releasing ultra low frequency acoustic wave in the lithosphere, it is possible to consider the interaction of two acoustic waves with frequencies Ω_1, Ω_2 and wave vectors K_1, K_2 excited by fracturing with elastic displacements in the rock by means of the elasticity theory. Due to nonlinear interaction in the lithosphere, it is possible to release an ultra low frequency acoustic wave (at a frequency Ω = Ω_1 - Ω_2). The analysis of the nonlinear interaction of two acoustic waves is based on the slowly varying profile method, and analytical and numerical modeling is given for the case of frequencies Ω1,2 ≈ 2 pi \cdot 500s-1, Ω ≈ 2 pi \cdot 3s-1.

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