Publication Date:
2009-03-03
Description:
Large data sets covering large areas and time spans and composed of many different independent sources raise the question of the obtained degree of harmonization. The present study is an analysis of the harmonization with respect to the moment magnitude Mw within the earthquake catalogue for central, northern, and northwestern Europe (CENEC). The CENEC earthquake catalogue (Grünthal et al., J Seismol, 2009) contains parameters for over 8,000 events in the time period 1000-2004 with magnitude Mw ≥ 3.5. Only about 2% of the data used for CENEC have original Mw magnitudes derived directly from digital data. Some of the local catalogues and data files providing data give Mw, but calculated by the respective agency from other magnitude measures or intensity. About 60% of the local data give strength measures other than Mw, and these have to be transformed by us using available formulae or new regressions based on original Mw data. Although all events are thus unified to Mw magnitude, inhomogeneity in the Mw obtained from over 40 local catalogues and data files and 50 special studies is inevitable. Two different approaches have been followed to investigate the compatibility of the different Mw sets throughout CENEC. The first harmonization check is performed using Mw from moment tensor solutions from SMTS and Pondrelli et al. (Phys Earth Planet Inter 130:71-0101, 2002; Phys Earth Planet Inter 164:90-112, 2007). The method to derive the SMTS is described, e.g., by Braunmiller et al. (Tectonophysics 356:5-22, 2002) and Bernardi et al. (Geophys J Int 157:703-716, 2004), and the data are available in greater extent since 1997. One check is made against the Mw given in national catalogues and another against the Mw derived by applying different empirical relations developed for CENEC. The second harmonization check concerns the vast majority of data in CENEC related to earthquakes prior to 1997 or where no moment tensor based Mw exists. In this case, an empirical relation for the Mw dependence on epicentral intensity (I0) and focal depth (h) was derived for 41 master events, i.e., earthquakes, located all over central Europe, with high-quality data. To include also the data lacking h, the corresponding depth-independent relation for these 41 events was also derived. These equations are compared with the different sets of data from which CENEC has been composed, and the goodness of fit is demonstrated for each set. The vast majority of the events are very well or reasonably consistent with the respective relation so that the data can be said to be harmonized with respect to Mw, but there are exceptions, which are discussed in detail. © Springer Science+Business Media B.V. 2009.
Print ISSN:
1383-4649
Electronic ISSN:
1573-157X
Topics:
Geosciences
,
Physics
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