Seismological Characteristics
Seismological Characteristics

Seismological characteristics of Dubrovnik region

Earthquakes' data at the territory of Croatia go back to 373 B.C. when a very strong earthquake destroyed Cavtat. Two earthquakes had the intensity of X° MCS scale: the earthquake in 361 when the town Cissa at the island of Pag is stated to have fallen in the sea and by all means the earthquake in Dubrovnik from 1667. Besides those earthquakes the territory of Croatia had 21 earthquakes till today with the intensity of IX° MCS scale.

Historic data state that Dubrovnik has been severely struck by earthquakes many times through its history. In the catalogue of earthquakes in Croatia and its neighbouring regions done by the Geophysical department of the faculty of Science at the University of Zagreb (hereinafter "Catalogue") the oldest information is related to the aforesaid earthquake in 373 B.C. Strong earthquakes are stated in 376, 1471, 1482, 1504, 1516 and 1520 which caused serious damages to the City of Dubrovnik. It is the matter of historic earthquakes and their features have not been reliably proved. But the earthquake on 6th April 1667 certainly happened near Dubrovnik and its maximal intensity was X? of MCS scale. It has been the most important earthquake so far as there has been no stronger earthquake on the territory of Dubrovnik after it. The whole City was practically demolished and over 5.000 people lost their lives. After the earthquake the City was caught by fire that destroyed the remains. Over 200 people were killed in Kotor, over 70 of them in Budva and 40 in Perast. The figures indicate huge damages caused by this earthquake from Podgora to Ulcinj. In Ston half of the houses were demolished and all what was placed in the plains. During the earthquake the sea was swinging in the Venetian canals and it was felt by residents of Napoli, Smirna and Istanbul. The sea in Dubrovnik withdrew several times and then came back. The data mention many additional earthquakes that were felt every day after the main one as well as a continuous thudding from the sea side.

In the recent history two earthquakes should be mentioned, those in 1850 and 1869 which in Dubrovnik had intensity of VII° MCS scale. On 15th April 1979 the earthquake happened at the distance of some 100 km from Dubrovnik in the seabed of Montenegrin littoral. Its magnitude was 7.0 and it had disastrous impact. The earthquake manifested also in Dubrovnik with intensity of VII° MCS scale without huge impacts on the vital city buildings. Nevertheless it caused high material damages and its reconstruction lasted a long period.

In 1995 there was a series of earthquake took place around Dubrovnik with epicentre distances of Dubrovnik in range of 15 km. In the period of 6 months there were over 150 earthquakes and 108 of them were located. The strongest one was on 28th September 1995 with epicentre in the seabed between Dubrovnik and Cavtat, around 6 km far from the centre of Dubrovnik. Its magnitude was 5.0 with focus on the depth of about 5 km. The maximal intensity was VI° of MCS scale. Fortunately it caused only minor damages in Dubrovnik area.

By all means the most significant series of earthquakes in the recent history began on 9th September 1996 with the earthquake of magnitude 5.9 and the epicentre in the seabed between Ston and Slano. Depth of focus was 11 km and maximal intensity of VIII° MCS scale with single effects in the historic centre of Ston and IX° of MCS scale. That earthquake was manifested in Dubrovnik by intensity of V° MCS scale (the map showed on Picture 6). Series of additional earthquakes that followed lasted over two years. It was registered over 3.000 earthquakes and 1350 of them were located. As presented on Picture 7 (overtaken from the work of Markušić et al.) the migration of epicentres happened in the vast area with major part on the territory between Slano and Ljubinje in Bosnia and Herzegovina.

Intensities of earthquakes in the region of Dubrovnik which, according to the Seismological map of Croatia (Kuk, 1987), correspond to particular retroactive periods, are shown in the Table 2 (pursuant to definition the response period is the central interval in years that run between two successive surpasses of quoted intensities of earthquakes with probability of 63%).