2 nd WORKSHOP OF THE NATO SfP 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 Institute of Geosciences, Energy, Water and Environment Polytechnic University of Tirana

Investigating the data for the earthquakes occurred within Albania, examining for missing or duplicated events, as well as improvement of their location and magnitude characterization. Two catalogues of earthquakes are prepared: 1) Catalogue of Albanian earthquakes with M S ≥4.5, for the time period 58BC This catalogue comprises earthquakes occurred within the area with geographical coordinates N and E. 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 M L ≥3.0, for the time period /12/2011. The catalogue contains events, occurred within the area with geographical coordinates [ N; E]. Reported magnitudes and the relevant references are given for this earthquake catalogue. UPGRADING EARTHQUAKE CATALOGUES I G E W E, P U T

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) , for the historical earthquakes ( Location is generally obtained from Macroseismic Data Points (MDPs) processing. M W has been calculated as the weighted mean of M W from MDPs, and the epicentral intensity I O. 2) ISC-GEM Global Instrumental Earthquake Catalogue ( ), 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. UPGRADING EARTHQUAKE CATALOGUES I G E W E, P U T

he unified earthquake catalogue should be in terms of M W. We propose to use the following strategy: 1) Where possible, to use existing direct measurements of M W from Global CMT (Harvard) and RCMT (INGV, ETHZ) projects for the period , giving a priority to them. For earthquakes in the period , the new ISC-GEM catalogue (2012) contains also estimations of M 0 (and consequently M W ) based on a comprehensive search of quality scientific articles. 2) In all other instances, we should compute M W proxy values based on the available data (macroseismic intensities for historical period, M L and/or M S, m b for the instrumental period), using updated regression models. To obtain the most homogenous record of earthquakes for consequent hazard assessment, the unified earthquake catalogue should be in terms of M W. We propose to use the following strategy: 1) Where possible, to use existing direct measurements of M W from Global CMT (Harvard) and RCMT (INGV, ETHZ) projects for the period , giving a priority to them. For earthquakes in the period , the new ISC-GEM catalogue (2012) contains also estimations of M 0 (and consequently M W ) based on a comprehensive search of quality scientific articles. 2) In all other instances, we should compute M W proxy values based on the available data (macroseismic intensities for historical period, M L and/or M S, m b for the instrumental period), using updated regression models. UNIFICATION OF THE MAGNITUDE SCALES I G E W E, P U T

The procedure followed in BSHAP needs to be improved: 1) The events used to derive the empirical relations for M L to M W 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 ) Defining an alternative procedure (M. Herak) to convert local magnitudes for small events (M<4.0), because M W determinations used to derive the relevant empirical relations were available only for moderate size and strong earthquakes (M W ≥4.0). E xtrapolation of empiric relations beyond the magnitude range of events used for their deriving should be avoided. The procedure followed in BSHAP needs to be improved: 1) The events used to derive the empirical relations for M L to M W 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 ) Defining an alternative procedure (M. Herak) to convert local magnitudes for small events (M<4.0), because M W determinations used to derive the relevant empirical relations were available only for moderate size and strong earthquakes (M W ≥4.0). E xtrapolation of empiric relations beyond the magnitude range of events used for their deriving should be avoided. UNIFICATION OF THE MAGNITUDE SCALES I G E W E, P U T

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 M W proxy values can be obtained using regression relations between M W and M S, or between M W and m b from the ISC-GEM catalogue. 4a) The surface wave magnitude M S is proven to be a good estimator of M W, since it scales rather well in a wide range of magnitudes. 4a1) In the BSHAP we have derived and used the relation (Fig. 1): 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 M W proxy values can be obtained using regression relations between M W and M S, or between M W and m b from the ISC-GEM catalogue. 4a) The surface wave magnitude M S is proven to be a good estimator of M W, since it scales rather well in a wide range of magnitudes. 4a1) In the BSHAP we have derived and used the relation (Fig. 1): M W = 1/( – M S ) n=293, s e =0.176, 3.0 ≤ M S ≤ 7.0 UNIFICATION OF THE MAGNITUDE SCALES I G E W E, P U T

Figure 1. Regression relation between M W and M S (BSHAP) UNIFICATION OF THE MAGNITUDE SCALES

4a2) In the ISC-GEM catalogue, an exponential model is used: M W = exp ( M S ) b) Differently from M S, the short-period body-wave mag. m b has a larger scatter with M W, especially for eqs with mag. above 6. 4b1) In the framework of BSHAP we have derived the relation (Fig. 2): n=367, s e =0.198, In the ISC-GEM catalogue, an exponential model is used: M W = exp ( M S ) , Both models suffer from the saturation of m b for larger eqs, and tend to underestimate the M W value. Therefore m b can be used only when M S is not available to obtain a proxy M W. 4a2) In the ISC-GEM catalogue, an exponential model is used: M W = exp ( M S ) b) Differently from M S, the short-period body-wave mag. m b has a larger scatter with M W, especially for eqs with mag. above 6. 4b1) In the framework of BSHAP we have derived the relation (Fig. 2): M W = 1/( – M B ) n=367, s e =0.198, 3.5≤m b ≤6.2 4b2) In the ISC-GEM catalogue, an exponential model is used: M W = exp ( M S ) , 3.5≤m b ≤6.8 Both models suffer from the saturation of m b for larger eqs, and tend to underestimate the M W value. Therefore m b can be used only when M S is not available to obtain a proxy M W.. UNIFICATION OF THE MAGNITUDE SCALES I G E W E, P U T

Figure 2. Relationship between M W and the mb (BSHAP) 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 M W values in the following order: 1) M W GCMT (Harvard catalogue) or RCMT (INGV, ETHZ). 2) M W from bibliographic search (included in the ISC-GEM catalogue). 3) M W proxy based on M L and regression/procedure of the country where the earthquake occurred. 4) M W proxy based on M S found in the ISC bulletins. 5) M W proxy based on m b found in the ISC bulletins. In case of M W proxy based on M L and M S, or M L and m b, the weighted mean of these estimates may be a good choice. to convert M L for the small events (M<4.0), 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 M W values in the following order: 1) M W GCMT (Harvard catalogue) or RCMT (INGV, ETHZ). 2) M W from bibliographic search (included in the ISC-GEM catalogue). 3) M W proxy based on M L and regression/procedure of the country where the earthquake occurred. 4) M W proxy based on M S found in the ISC bulletins. 5) M W proxy based on m b found in the ISC bulletins. In case of M W proxy based on M L and M S, or M L and m b, 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 M L for the small events (M<4.0), UNIFICATION OF THE MAGNITUDE SCALES I G E W E, P U T

Thank You !