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Improvement and Harmonization of Albania BSHAP Earthquake Catalogue Neki Kuka

2 nd WORKSHOP OF THE NATO SfP 984374 PROJECT “Improvements in the Harmonized Seismic Hazard Maps for the Western Balkan Countries” April 25-26, 2013 Belgrade, Serbia. Improvement and Harmonization of Albania BSHAP Earthquake Catalogue Neki Kuka

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Improvement and Harmonization of Albania BSHAP Earthquake Catalogue Neki Kuka

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  1. 2nd WORKSHOP OF THENATO SfP 984374 PROJECT“Improvements in the Harmonized SeismicHazard Maps for the Western Balkan Countries”April 25-26, 2013Belgrade, Serbia Improvement and Harmonization of Albania BSHAP Earthquake CatalogueNeki Kuka Institute of Geosciences, Energy, Water and Environment Polytechnic University of Tirana

  2. UPGRADING earthquake Catalogues Investigating the data for the earthquakes occurred within Albania, examining for missing or duplicated events, as well as improvement of their location and magnitudecharacterization.Two catalogues of earthquakes are prepared:1) Catalogue of Albanian earthquakes with MS≥4.5, for the time period 58BC-2012. This catalogue comprises earthquakes occurred within the area with geographical coordinates 39.00-43.00N and 18.50-21.50E. The catalogue includes in total 715 earthquakes, from which 585 are main shocks, and 130 are for/aftershocks.2) Catalogue of the Albanian earthquakes with ML≥3.0, for the time period 1964-31/12/2011. The catalogue contains 21536 events, occurred within the area with geographical coordinates [38.00-43.85N; 18.00-22.00E]. Reported magnitudes and the relevant references are given for this earthquake catalogue. I G E W E, P U Twww.geo.edu.al

  3. UPGRADING earthquake Catalogues A final comparison and verification with the earthquakes catalogues made public in 2012, is planned for the next six-month:1) SHARE European Earthquake Catalogue (SHEEC) 1000-1899, for the historical earthquakes (http://emidius.eu/SHEEC/).Location is generally obtained from Macroseismic Data Points (MDPs) processing. MW has been calculated as the weighted mean of MW from MDPs, and the epicentral intensity IO.2) ISC-GEM Global Instrumental Earthquake Catalogue (1900-2009), created on the request and with sponsorship of GEM Foundation.With a few exceptions, parameters of this catalogue are the result of computations based on the original reports of seismic stations and observatories, using uniform location and magnitude determination procedures during the entire period of the catalogue. I G E W E, P U Twww.geo.edu.al

  4. Unification of the magnitude scales To obtain the most homogenous record of earthquakes for consequent hazard assessment, the unified earthquake catalogueshould be in terms of MW. We propose to use the following strategy:1) Where possible, to use existing direct measurements of MW from Global CMT (Harvard) and RCMT (INGV, ETHZ) projects for the period 1976-2013, giving a priority to them. For earthquakes in the period 1900-1979, the new ISC-GEM catalogue (2012) contains also estimations of M0 (and consequently MW) based on a comprehensive search of quality scientific articles.2) In all other instances, we should compute MW proxy values based on the available data (macroseismic intensities for historical period, ML and/or MS, mb for the instrumental period), using updated regression models. I G E W E, P U Twww.geo.edu.al

  5. Unification of the magnitude scales The procedure followed in BSHAP needs to be improved:1) The events used to derive the empirical relations for ML to MW conversion, for every country must be verified, especially the local magnitude. For Albania and Serbia, the data used are verified.2) Updating the regression relations using new data (CMT+RCMT, and the relevant local magnitudes) for the period 2010-2013.3) Defining an alternative procedure (M. Herak) to convert local magnitudes for small events (M<4.0), because MW determinations used to derive the relevant empirical relations were available only for moderate size and strong earthquakes (MW≥4.0). E xtrapolation of empiric relations beyond the magnitude range of events used for their deriving should be avoided. I G E W E, P U Twww.geo.edu.al

  6. Unification of the magnitude scales 4) There are o lot of eqs in the early instrumental period (and before beginning of GCMT catalogue in 1976), where no direct measurements of seismic moments are available, especially for strong eqs. The MWproxy values can be obtained using regression relations between MW and MS, or between MW and mbfrom the ISC-GEM catalogue.4a)The surface wave magnitude MSisproven to be a good estimator of MW, since it scales rather well in a wide range of magnitudes. 4a1) In the BSHAP we have derived and used the relation (Fig. 1):MW = 1/(0.31304 – 0. 024282MS)n=293, se=0.176,3.0 ≤ MS ≤ 7.0 I G E W E, P U Twww.geo.edu.al

  7. Unification of the magnitude scales Figure 1. Regression relation between MW and MS (BSHAP)

  8. Unification of the magnitude scales . 4a2) In the ISC-GEM catalogue, an exponential model is used:MW = exp(-0.22+0.23MS) + 2.864b)Differently from MS, the short-period body-wave mag. mb has a larger scatter with MW, especially for eqswith mag. above 6.4b1) In the framework of BSHAP we have derived the relation (Fig. 2):MW = 1/(0. 40266 – 0. 041342mb) n=367, se=0.198, 3.5≤mb≤6.24b2)In the ISC-GEM catalogue, an exponential model is used:MW = exp(-4.66+0.86MS) + 4.56, 3.5≤mb≤6.8Both models suffer from the saturation of mb for larger eqs, and tend to underestimate the MW value. Therefore mbcan be used only when MS is not available to obtain a proxy MW . I G E W E, P U Twww.geo.edu.al

  9. Unification of the magnitude scales Figure 2. Relationship between MWand the mb(BSHAP)

  10. Unification of the magnitude scales In order to provide the most reliable magnitude value for every earthquake in the catalogue, in case of several magnitude estimates available for a single earthquake, we propose to give priority to MW values in the following order:1) MW GCMT (Harvard catalogue) or RCMT (INGV, ETHZ).2) MW from bibliographic search (included in the ISC-GEM catalogue).3) MW proxy based on ML and regression/procedure of the country where the earthquake occurred.4) MW proxy based on MS found in the ISC bulletins.5) MW proxy based on mbfound in the ISC bulletins.In case of MW proxy based on ML and MS, or ML and mb, the weighted mean of these estimates may be a good choice.For the next six months:1) A new update of the relevant relations is planned to be done.2) Defining the procedure to convert ML for the small events (M<4.0), I G E W E, P U Twww.geo.edu.al

  11. Thank You !

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