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CROATIAN EARTHQUAKE CATALOG
Ines IvančićCroatian Seismological Survey, Department of
Geophysics, Faculty of Science, University of Zagreb, Zagreb
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
Croatian earthquake
catalog 373BC – 2011
Croatia and the surrounding areas
41.7 – 46.7 N12.7 – 19.7 E
47524 earthquakes
Croatian earthquake catalogEstimating the completeness
Vertical lines indicate
change in catalogue completeness
Historical earthquakes
76 ye
ars
30 years
7 ye
ars
Time distribution of seismic events (mainshocks) by year, (ML ≥ 2.0)
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)
Frequency-magnitude distribution
Noncum. FMD
• 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
373BC-1907975 earthquakes
Croatian earthquake catalog
1908-19742680 earthquakes
Continuous instrumentalrecording of earthquakes since 1908.
Year1908 Small horizontal
mass 80 kg
Year 1909Large horizontalmass 1000 kg
Wiechert mechanical seismographs:
Andrija Mohorovičić
Seismographic stations
1908
Seismographic stations
Croatian earthquake catalog
1975-2004 18718 earthquakes
1975 –seismographic network improvements
1975 2005Seismographic stations
Croatian earthquake catalog
2005 - 201125151 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
Croatian earthquake catalog
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
• 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 – 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
Magnitude determination
Indi
vidu
al (s
tatio
n) m
agni
tude
sEa
rthq
uake
mag
nitu
des
MW vs. MWA MW vs. ML ML vs. MWA
Magnitude determination
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 500000 phase readings)•Macroseismic data (380 events) and maps archive •Digital seismograms•Strong-motion data
relational database
relational database enables easy acces and management of data
Croatian Earthquake Database – Queries
Earthquake catalogue
Table of relations
Macroseismic catalogue
Query1: Finding the macroseismic intensity in Samobor for the Pokupsko earthquake in 1909Query2: corresponding macroseismic map
Earthquakes felt in Samobor
STON – SLANO
1996.
Imax = VIII MCS
M = 6.0
Croatian Earthquake Database – Queries
ML-max per year (1900-2011)
Croatian earthquake catalogueSome statistics…
Kni
n
Bio
kovo
Mon
te N
egro
Jabu
ka
Isla
ndSto
n
Number of earthquakes(M ≥ 3.0) per year
Significant earthquake sequencies
The most seismically active areas in Croatia are:-Greater Zagreb area (NW Croatia)
- Croatian Primorje
- Dalmatia (SE Croatia)
The strongest earthquakes in CroatiaML ≥ 6.0
Red dots: events after 1850Yellow dots: 373BC - 1850
Croatian earthquake catalogue
BSHAPEpicenter Map for
Croatia and Adjacent
Areas
373 BC – 2011
•3398 earthquakes ML ≥ 3.0
•D ≤ 15 km of the Croatian border
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
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.