CROATIAN EARTHQUAKE CATALOG

1. CROATIAN EARTHQUAKE CATALOG Ines Ivančić Croatian Seismological Survey, Department of Geophysics, Faculty of Science, University of Zagreb, Zagreb

2. CROATIAN EARTHQUAKE CATALOG (CEC) • The gathering of seismological data in Croatia has a history longer than a century • continuous instrumental observations since 1908 (Zagreb seismological station) • The CEC has been compiled using all data on earthquakes from the archives of the Department of Geophysics, Faculty of Science, University of Zagreb(the catalogues, macroseismic reports, seismograms, and other related documents…) • Its first revision was described by Herak, M., Herak, D. and Markusic, S. (1996) • The catalogue is routinely updated • hypocentral locations and magnitudes are obtained through location procedure using all data from Croatian stations as well as those reported by other regional networks

3. Croatian earthquake catalog 373BC – 2011 Croatia and the surrounding areas 41.7 – 46.7 N12.7 – 19.7 E 47524 earthquakes

4. Croatian earthquake catalog Estimating the completeness Frequency-magnitude distribution Time distribution of seismic events (mainshocks) by year, (ML≥ 2.0) Noncum. FMD 1908-1974: MC ≥ 4.0, (bML = –0.86); 1975-2004: MC ≥ 3.0, (bML= –0.94); 2005-2011: MC ≥ 2.0, (bML= –0.90); (max.-likelihood b-value, after Gutenberg-Richter relationship) Historical earthquakes 76 years Vertical lines indicate change in catalogue completeness 30 years 7 years

5. Croatian earthquake catalog 373BC-1907 975 earthquakes • 1879 – Dr. Mijo Kišpatić: First comprehensive chronicle of earthquakes (from 1502 – 1879) • 1880 – the major Zagreb earthquake was the main impetus for the scientific study of earthquakes in Croatia

6. Croatian earthquake catalog Andrija Mohorovičić 1908-1974 2680 earthquakes Wiechert mechanical seismographs: Year1908 Small horizontal mass 80 kg 1908 Year 1909 Largehorizontal mass1000 kg Continuous instrumental recording of earthquakes since 1908. Seismographicstations Seismographicstations

7. Croatian earthquake catalog 1975 –seismographicnetworkimprovements 1975-2004 18718 earthquakes Seismographicstations 1975 2005

8. Croatian earthquake catalog • 2005 - 2011 • 25151 earthquakes • 2005 – … • increasing the number of seismographicstations • furtherupgrading of seismographic stations with the installation of digital equipment • All stations are transmiting the data to Zagreb in real-time Seismographicstations Croatian seismographic network

9. Magnitude determination • For earthquakes before 1908 cataloglists magnitude Mm computed from intensity • The magnitude MLformulaapplied by our Departmentwasderived in the ‘Balkan project’ (1974). It was retained even after introduction of electromagnetic and digital seismographs: • Magnitude revision for the events after the installation of digital seismographs yielded new calibrating functions for local magnitudes (ML and MWA) which produce distance-independent estimates • Amax is the trace amplitude in nm on the simulated Wood-Anderson seismograph (magnification 2080); • SC is station correction

10. Magnitude determination • Magnitude MLis determined from station ZAG until the year 2005. • After the year 2005 magnitude MLis the median magnitude from Croatian stations • Magnitudes MLwere recalculated for each Croatian station with new calibrated function for local magnitudes in the period 2005 – 2011 and the median magnitude was determined for each event • The correspondence between the three magnitudes is close to 1:1 relationship – enabling an easy conversion from ML to MW

11. Magnitude determination Individual (station) magnitudes Earthquake magnitudes MW vs. MWA ML vs. MWA MW vs. ML

12. CroatianEarthquakeDatabase Accumulationof all kindsofseismicity-relateddata invariousfilesandshapes: • Earthquakerecords(> 55,000 in 2012) • Fault-plane solutions(>200 earthquakes) • Phasereadings for all analysedearthquakes(>35,000 fileswithover500000 phasereadings) • Macroseismic data (380 events) andmapsarchive • Digitalseismograms • Strong-motion data relational database enables easy acces and management of data relational database

13. Croatian Earthquake Database – Queries Query1: Finding the macroseismic intensity in Samobor for the Pokupsko earthquake in 1909 Query2: corresponding macroseismic map Macroseismic catalogue Table of relations Earthquake catalogue Earthquakes felt in Samobor

14. Croatian Earthquake Database – Queries STON – SLANO 1996. M = 6.0 Imax = VIII MCS

15. Croatian earthquake catalogueSome statistics… ML-max per year (1900-2011) Number of earthquakes(M≥ 3.0) per year Significant earthquake sequencies Jabuka Island Ston Monte Negro Knin Biokovo

16. Croatian earthquake catalogue The most seismicallyactive areas in Croatia are: • Greater Zagreb area (NW Croatia) • Croatian Primorje • Dalmatia(SE Croatia) The strongest earthquakes in Croatia ML≥ 6.0 Red dots: events after 1850 Yellow dots: 373BC - 1850

17. BSHAP Epicenter Map for Croatia and Adjacent Areas 373 BC – 2011 3398 earthquakes ML≥ 3.0 D ≤ 15 km of the Croatian border

18. Croatian earthquake catalogue BSHAP format • Magnitude MLdeterminedfrom station ZAG. After 2005, this is themedian magnitude fromCroatianstations • Magnitude MLdeterminedfromothersources • Reference list is verifiedandupdatedwithrespect to BSHAP sourcecodes

19. Conclusions • Magnitude revision yielded new calibrating functions for local magnitudes (ML and MWA). Magnitudes were recalculated with new calibrated function for local magnitudes in the period 2005 – 2011. • The correspondence between the three magnitudes is close to 1:1 relationship, enablingeasy conversion from ML to MW. • A procedure for routine computation of moment magnitude using spectra of local and regional earthquakes has been established. • Croatian Earthquake Database is a significant effort towards data organization and usability. • The completeness of the Croatian earthquake catalog has been investigated. • Duplicate events were removed. • Reference list was verified and updated with respect to BSHAP source codes.