Lateral variations of the local magnitude at Ebre station,Northeastern Iberian Peninsula |
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Authors: | Josep Vila Josep Batllo Antoni M. Correig |
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Affiliation: | (1) Department d'Astronomia i Meteorologia, Facultat de Fisica, Universitat de Barcelona, Martí i Franquès, 1, E-08028 Barcelona, Spain;(2) Laboratori d'Estudis Geofisics Eduard Fontserè, Institut d'Estudis Catalans, Facultat de Física, Martí i Franquès, 1, E-08028 Barcelona, Spain;(3) Observatori de l'Ebre, CSIC, E-43520 Roquetes, Tarragona, Spain |
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Abstract: | Since 1984, a seismic surveillance at the Baix Ebre Region (NE of the Iberian Peninsula) has been carried out from a seismic network consisting of two digital and one analog stations. Large discrepancies between the recorded amplitudes and the magnitude estimates given by different agencies have been observed. To explain these discrepancies, that consist of a large reduction of amplitude and a strong dependence of the azimuth, a local magnitude formula for the area has been computed, using the analog records obtained at EBR short-period station. Global results show an average station correction factor between the computed local magnitude and the reported magnitude of the order of 1, presenting large variations around the mean value with a clear dependence on the azimuth. A detailed analysis of this variation around the mean value reveals that earthquakes can be classified according to their location in different geological units, thus obtaining for each zone a distinct station correction factor that can fluctuate as much as 0.6 around the average. These large lateral variations of the magnitude are in good agreement with previous studies of coda-Q attenuation. |
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Keywords: | Local magnitude lateral variations station correction term |
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