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Automatic solutions (compression quadrants in red)

Automatic solutions are obtained with the FMNEAR method (Delouis, 2014) which inverts the bandpass filtered displacement waveforms of broadband and strong motion records at local to regional distance searching for the double couple focal mechanism. Depending on magnitude, the source is represented either by a point source (M < 5.5) or by a linear extended source model oriented along fault strike (M > 5.5). The use of an extended source model allows us to model the waveforms of large earthquakes using near source strong motion records. The parameter space for the strike, dip, and rake parameters of the focal mechanism is explored in a nonlinear way allowing the evaluation of the degree of uniqueness of the solution, which is quantified through a 'confidence index'. Source depth and moment magnitude (Mw) are also recomputed. The overall quality of the solution is indicated by a letter, A, B, C based on the index of confidence and the number of components used. ‘A’ means that the focal mechanism is strongly constrained, ‘B’ well constrained, ‘C’ moderately constrained. Solutions too poorly constrained are not shown.

FMNEAR inversion is triggered when a new event is located, either by sismoazur (focused on south-east France and neighboring areas), or by the EMSC (global scale). Different trigger magnitude thresholds are used depending on the geographical area. If too few records at local to regional distance are available from the open data centers, no solution will be provided. This catalogue of focal mechanisms will be far from exhaustive. The moment magnitude Mw results from the waveform inversion.

These solutions are published in a fully automated way, without revision.

Manually revised solutions (compression quadrants in blue)

These solutions have been obtained with a methodology which may have evolved through time but were manually determined. They were obtained by waveform inversion and/or by using the first motion data (P wave polarities). A value of Mw is provided only in the case of waveform inversion.

Reference: Delouis, B., 2014. FMNEAR: determination of focal mechanism and first estimate of rupture directivity using near source records and a linear distribution of point sources, Bulletin of the Seismological Society of America, 104 (3), 1479-1500, doi:10.1785/0120130151.