CROATIAN EARTHQUAKE
CATALOG
Ines Ivančić
Croatian 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 N
12.7 – 19.7 E
47524 earthquakes
Croatian earthquake catalog
Estimating the completeness
Time distribution of
seismic events
(mainshocks) by year,
(ML ≥ 2.0)
Frequency-magnitude
distribution
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)
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
Croatian earthquake catalog
1908-1974
2680 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
Croatian earthquake catalog
1975-2004
18718 earthquakes
1975 –
seismographic
network
improvements
Seismographic stations
1975
2005
Croatian earthquake catalog
2005 - 2011
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
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 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 – 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
Earthquake magnitudes
Individual (station) magnitudes
Magnitude determination
MW vs. MWA
MW vs. ML
ML vs. MWA
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 enables easy
acces and management of data
relational database
Croatian Earthquake Database – Queries
Macroseismic
catalogue
Earthquake
catalogue
Table of
relations
Earthquakes felt in Samobor
Query1: Finding the macroseismic intensity in
Samobor for the Pokupsko earthquake in 1909
Query2: corresponding macroseismic map
Croatian Earthquake Database – Queries
STON –
SLANO
1996.
M = 6.0
Imax = VIII MCS
Croatian earthquake catalogue
Some statistics…
ML-max per year (1900-2011)
Number of earthquakes
(M ≥ 3.0) per year
Croatian earthquake catalogue
The most seismically active
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
BSHAP
Epicenter 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.