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Bucharest. European capital city with the most vulnerable response to a strong earthquake/ București. Capitala europeană cea mai vulnerabilă la un cutremur puternic



Although the seismic activity in Romania that represents the greatest threat to society is concentrated in a small area at the Carpathians arc bend (Vrancea source) at intermediate depth (60 – 180 km depth), the effects of the large earthquakes (Mw > 7) are unusually strong and were reported at unusually large distances on a north-east to south-west direction. In particular, the impact of Vrancea earthquakes on Bucharest city, as observed over several centuries, was so severe that Bucharest is currently considered the most vulnerable European capital city to earthquakes. For this reason, microzoning and seismic risk studies for Bucharest city have emerged after 1977 and still constitute a priority research direction in our country. The present book reviews the most significant results obtained in recent years in this field of research. These results refer to several major fields of study that are included in the nine chapters of the book:

Geographical, geomorphological and geotectonic framework of the city area;
Geological modelling in the Bucharest area;
Hydrogeology conditions in Bucharest underground and its influence upon the site effects;
Seismic hazard at regional (Romania) and local scale (Bucharest area);
Application using GNSS technology to evaluate geodynamic movements;
Geophysical measurements in the city underground;
Modelling of the local structure in the Bucharest metropolitan area using ambient vibration analysis;
A view of seismic hazard assessment in Romania and implications for associated seismic risk in Bucharest city;
Early Warning System developed and implemented for Bucharest city;
Vulnerability and seismic risk scenarios for Bucharest city.

It is worth mentioning that most of the presented results have been obtained within the last Nucleu program, “Multidisciplinary research of the seismic phenomenon in order to increase resilience to earthquakes” (MULTIRISC), financed by the Ministry of Research, Innovation and Digitization of Romania, carried out between 2019 and 2022.

At the same time, we appreciate that the results presented in this book are an accomplishment of the Romanian researchers in the National Institute for Earth Physics during 45 years of activity since 10 January 1977 when the institute was founded.

Considering the complexity of the approach, the results presented in the volume required the development of multidisciplinary researches, involving seismology, geology, geophysics, geotectonics, hydrogeology and geodesy. Basically, the investigations set out the fundamental role played by an unfavourable mixture of factors that leads to such large effects in the Bucharest city area as a result of the occurrence of Vrancea earthquakes at epicentral distances greater than 120 km. Thus, the source radiation characterized by large periods (around 1.5 s for the major earthquakes) and directivity effects towards SW of Vrancea, combined with very efficient wave propagation at depth along this direction and matching the seismic response of the local structure beneath the city and the resonance of the tall buildings to large periods, all these factors together lead to unusual amplifications of strong ground motion. And this potentially endangering situation, together with the vulnerability of the structures built before 1977, and especially those erected in the period 1920 – 1940, explains why in the case of the city of Bucharest we are talking about one of the highest levels of risk reported around the world. In addition, hydrogeological and geophysical on-site investigations regarding the characteristics of the superficial layers, bring additional elements that contribute to increasing the risk caused by the seismic motion (local amplifications, soil liquefaction and instabilities).

The thorough knowledge of all the factors and disastrous processes that lead to loss of human life and buildings and infrastructure damage is of paramount importance for the prevention and reduction of damage during future earthquakes.

We believe that this book provides an useful state-of-the-art and will bring a major contribution to the knowledge of the seismic hazard assessment and will offer useful tools and methods of action for all public organisms interested in contributing to the prevention of at least some of the catastrophic effects of earthquakes, as well as to the mitigation of the seismic risk, so that the city of Bucharest becomes a safer and favourable place for its inhabitants and a continuous sustainable development.

Prof. dr. Mircea Radulian

Member of the Academy of Romanian Scientists

Correspondent Member of the Romanian Academy

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