Inverting full waveforms into 1D seismic velocity model of the upper crust by neighborhood algorithm - Corinth Gulf, Greece
Abstract
We investigated inversion of full waveforms into formal 1D velocity models. 'Formal' means that the models are primarily intended to simulate complete seismograms close to real records, rather than to reflect the true crustal structure from the geological point of view. The method is demonstrated for a magnitude M-w 5.3 earthquake (centroid depth of 4.5 km), recorded at 8 three-component stations in the Corinth Gulf region, Greece, spanning the epicentral distance range from 15 to 102 km, and frequency range from 0.05 to 0.2 Hz.
The forward problem was solved by the discrete wavenumber method, while the inversion was performed with the neighborhood algorithm. As such, not only the best-fit models, but also suites of the models almost equally well satisfying data were obtained.
The best resolution was found in the topmost similar to 10 km. Extensive testing of the model parametrization enabled identification of the most robust features of the solution.
The P- and S-wave velocities are characterized by a strong increase with depth in the topmost similar to 4-5 km. This part of the model can be approximated by a layer with constant velocity gradient.
Compared to a previously existing model of the region, the satisfactory waveform match was extended from the maximum frequency of 0.1 Hz up to 0.2 Hz. This extension will improve calculation of the seismic source parameters in the region, e.g. determination of source time functions and slip distributions of potential future M-w > 6 events.