MARINE HAZARD ASSESSMENT IN THE BLACK SEA BASIN. CASE STUDY-THE TSUNAMI PHENOMENON

Limited by active fault systems and showing a high regional seismicity, the Black Sea basin represents a suitable area for the occurrence of natural hazards, including the tsunami-type waves. The characteristic features of the Romanian seashore, bordered by a very large shelf area with low water depths and seashore topography, make it vulnerable to such phenomenon. Historical recordings of extreme natural events is almost lacking in Romania. Other circum-Black Sea countries (Turkey, Bulgaria, Ukraine), benefit from a large amount of historical evidence and have performed studies strictly focused on the tsunami-type natural hazard.

In Romania, the tsunami phenomenon, as marine natural hazard, is poorly documented. Along the Romanian coast anomalous hydrodynamic events occurred, usually described by eye-witnesses and rarely measured by instruments or mentioned in written documents. In several cases, subsequently to their occurrence, such phenomena are documented by visual or instrumental measurements, but their causes are difficult to interpret.

Geological investigations along the Romanian Black Sea shoreline reveal discontinuous occurrences of rocks with features recorded in “tsunamites”: strata with variable geometry and irregular boundaries resembling a sedimentary breccia, showing large clasts removed from the bedrock and containing a mixture of fossils of different geological ages (Pleistocene, Pliocene, Holocene) derived from different environments (marine, brackish, lacustrine).

Seismological studies identified active hypocenters around the Black Sea basin, high magnitude seismic events being considered as triggering the tsunami-type waves. Starting with 1945 the earthquakes were instrumentally recorded, the interpreted hypocenters depths ranging between 10 and 60 km. Most of these events occurred in the northern and north-eastern parts of the sea basin.

The complexity of the subject and lack of systematic data at national level require collecting new data, updating the existing information and increasing the data base with information from the circum-Black Sea countries. The appearance of such an event anywhere in the Black Sea basin would have significant effects on the coastal area, so a system of warning in real time and a manual with instructions in case of danger are in progress.