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 N 12.7 – 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
: MC ≥ 4.0, (bML = –0.86); : MC ≥ 3.0, (bML = –0.94);
: MC ≥ 2.0, (bML = –0.90);
(max.-likelihood b-value, after Gutenberg-Richter relationship)
Historical earthquakes
76 years
30 years
7 years
Vertical lines indicate change in catalogue completeness

5. Croatian earthquake catalog
373BC 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
earthquakes
Andrija Mohorovičić
Wiechert mechanical seismographs:
Year1908
Small horizontal
mass 80 kg
1908
Year 1909
Large horizontal
mass 1000 kg
Continuous instrumental
recording of earthquakes since 1908.
Seismographic stations
Seismographic stations

7. Croatian earthquake catalog
earthquakes
1975 – seismographic network improvements
Seismographic stations
1975
2005

8. Croatian earthquake catalog
25151 earthquakes
2005 – …
increasing the number of seismographic stations
further upgrading of seismographic stations with the installation of digital equipment
All stations are transmiting the data to Zagreb in real-time
Seismographic stations
Croatian seismographic network

9. Magnitude determination
For earthquakes before 1908 catalog lists magnitude Mm computed from intensity
The magnitude ML formula applied by our Department was derived 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 ML is determined from station ZAG until the year 2005.
After the year 2005 magnitude ML is the median magnitude from Croatian stations
Magnitudes ML were recalculated for each Croatian station with new calibrated function for local magnitudes in the period 2005 – 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
MW vs. ML
ML vs. MWA

12. Croatian Earthquake Database
Accumulation of all kinds of seismicity-related data in various files and shapes:
Earthquake records (> 55,000 in 2012)
Fault-plane solutions (>200 earthquakes)
Phase readings for all analysed earthquakes (>35,000 files with over phase readings)
Macroseismic data (380 events) and maps archive
Digital seismograms
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 catalogue Some statistics…
ML-max per year ( )
Number of earthquakes (M ≥ 3.0) per year
Knin
Biokovo
Monte Negro
Jabuka Island
Ston
Significant earthquake sequencies

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

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 ML determined from station ZAG. After 2005, this is the median magnitude from Croatian stations
Magnitude ML determined from other sources
Reference list is verified and updated with respect to BSHAP source codes

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, enabling easy 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.