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.