RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 8, ES1001, doi:10.2205/2005ES000195, 2006

Conclusions

[19]  There are different concepts of macroseismic intensity. Some seismologists suppose, that there are so many uncontrollable factors influencing the intensity of shaking in a given locality, that it makes no sense to look for any regularity in spatial distribution of intensities. In other words, it doesn't matter how big is discrepancy between intensities expected from equation (1) and reported in a locality. Especially, if the reported intensity referrers to original questionnaires, which, supposed, automatically ensures high accuracy of intensity assessments. Others assume that, though intensity is a complex phenomenon indeed, anyway, it is not a kind of miracle: mostly source magnitude, depth, and source-locality distance govern spatial distribution of intensities. Local ground effects are very important, too, but they cannot completely alter in general regular character of intensity distribution. The second concept being physically reasonable seems more preferable.

[20]  An obvious inconsistency between the reported parameters for the 2 June, 1930 earthquake in southern Catalonia in the IGN catalogue and the already published isoseismal maps for this seismic event provoked revision of the available data. The fact, that instrumental records, being absolutely independent from macroseismic ones, also prove a larger magnitude, than previously evaluated one, support the assumption that intensity of shaking is controlled (at least in general) by regular physical laws.

[21]  Comprehensive analysis of macroseismic and instrumental data leads to a remarkably good agreement in magnitude re-evaluation. Results show that the earthquake magnitude MS is within interval 4.5-4.8, which is significantly larger than the value previously reported in the IGN catalogue ( MS=3.9 ). The relatively accurate magnitude evaluation allows us also to assess the hypocenter depth to be at 20-30 km. On the other hand, the instrumental data analysis gives values of moment magnitudes Mw=4.4 for P waves and Mw=4.2 for S waves, also larger than the MS value previously reported. However, MS values should be larger than Mw, for Mw less than about 6 [Utsu, 2002]. Finally, results of the isoseismal map analysis of the 13 February, 1949 earthquake are in agreement with the previously reported magnitude and relatively shallow depth (10-15 km). Thus, it can be concluded that the occurrence of large earthquakes in southern Catalonia at various depths (from 10 km to 30 km) reflects presence of seismogenic structures there that are able to produce earthquakes with magnitudes at least as large as 4.5-4.8. The orientation of isoseismals lets us also to suggest that these seismogenic structures are oriented almost perpendicular to strike of elevations, which follow along the seashore. The modern topography does not inherit deep (low crust) structures. The same situation was observed near the western termination of the Caucasus near the Black Sea shore, as revealed by the Lower Kuban, November 9th, 2002 earthquake [Tatevossian et al., 2003]. In the latter case this conclusion was also supported by the fault plane solution: its strike was in remarkable agreement with the elongation of isoseismals.

\acknowledgements We are very indebted to José Manuel Mart nez-Solares and M. Aránzazu Izquierdo of the Instituto Geográfico Nacional (IGN), Madrid, Spain, for giving us all the macroseismic information of the IGN Database and for making us available digitally the IGN Seismic Catalogue. We also thank to Teresa Susagna, of the Catalonian Cartographic Institute and Fabra Observatory, who provided us with seismograms and macroseismic information on the southern Catalonia earthquakes. This work has been partially supported by a Scientific Program NATO grant, the RFBR grant 04-05-65004, and the MEC Projects HUM2004-04259/HIST and CGL2004-20332-E.


RJES

Citation: Tatevossian, R., A. Ugalde, J. Batlló, and R. Maciá (2006), Macroseismic and instrumental data comprehensive analysis: Earthquake of June 2, 1930 in Catalonia (Spain), Russ. J. Earth Sci., 8, ES1001, doi:10.2205/2005ES000195.

Copyright 2006 by the Russian Journal of Earth Sciences

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