The changes in the state of a geophysical medium before a strong earthquake can be found by studying of 3D seismic velocity images constructed for consecutive time windows. A preliminary step is to see changes with time in a minimum 1D model. In this paper we develop a method that finds the parameters of the minimum linear gradient model by applying a two-dimensional Taylor series of the observed data for the seismic ray and by performing least-square minimization for all seismic rays. This allows us to obtain the mean value of the discrete observed variable, close to zero value.
The modification of Gaussian elimination is described here as numerical method to determine the physically adequate solution of the linear equations system that is affected by complexity of the data error (measurements, parameterization et. al.). Other modifications and algorithms are mainly established to efficiently overcome calculating issues. In order to avoid influence of errors in the data the proposed technique selects a set of invertible sub-matrixes. Developing the Tikhonov regularization theory the regularized subsequence is determined for each unknown under consideration. Application of the method to local seismicity data derived high resolution areas and revealed that the hydrothermal field of high concentration CH4 and CO2 is surrounded by rock having high seismic velocity. Based on this result we conclude that nature protects the gas flow due to special structure, which is likely presented by dense basalt. Decrypt of satellite images shows that the zone of lowest elevation does not intersect this structure. Particularities of background seismicity are examined for the gas area being studied. Factors learned from nature experience permit us to formulate conditions to select a place for underground gas storage.
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