Andrei Bala

National Institute for Earth Physics · Department Geophysics Seismology and Seismotectonics

A significant growth in seismicity was recorded in 2023 in the Southern Carpa-thians and northern Banat region in Romania. The two earthquake sequences oc-curred close to Tg. Jiu (Gorj area) and Arad cities are the strongest episodes of seismicity ever recorded in these areas. The relocation of the hypocenters using Joint Hypocenter Method outlines...

The evaluation of seismic hazard at local scale, with the contribution of strong-motion data from a dense seismic network and insightful geological and geophysical data, is one of the key components in seismic risk mitigation. Significant efforts were made to record and predict the highly variable peak spectral amplification values of strong seismi...

In the past decades, the necessity for detailed earthquake microzonation studies was recognized for Bucharest city first because significant damage occurred here during the last major earthquakes, as well as for other densely populated cities in Romania exposed to major seismic risk due to the intermediate-depth earthquakes occurring in Vrancea zon...

Crustal structure and Neogene to Quarternary deformation in the southeastern Carpathians of Romania

A significant seismic sequence started on 13 Feb. 2023 at 14:58 GMT with a mainshock of 5.2 ML located at 17 km depth and at 14 km distance NW from Targu Jiu city. The first shock was followed by 16 aftershocks with magnitudes between 2.1 and 3.4 after which a second mainshock of magnitude 5.7 was triggered next day, 14 Feb., at 13:16 GMT. The larg...

Especially after the March 4, 1977 disastrous Vrancea earthquake (Mw 7.4), the necessity for a detailed local seismic hazard map for Bucharest, the capital city of Romania, was recognized. The distribution of earthquake effects as well as subsequent earthquake recordings throughout the city revealed a high variability of seismic ground motion, not...

In local seismic hazard studies, a first step is to have a precise local determination of the parameters of shallow soil layers which are very important input data in order to determine the local response under various seismic scenarios. The results will determine the local variability of the soil package down to a level that may induce significant...

Vrancea seismogenic zone in the South-Eastern Carpathians is characterized by localized intermediate-depth seismicity. Due to its complex geodynamics and large strain release, Vrancea represents a key element in the Carpatho-Pannonian system. Data from a recently compiled catalogue of fault plane solutions (REFMC) are inverted to evaluate stress re...

The mechanisms involved in the geodynamic evolution and the links with present day seismicity in and around an active orogenic area such as Vrancea area, located at the arc bend of the SouthEastern Carpathians in Romania, are of fundamental importance for studies concerning the seismic hazard assessment in Romania. The task is attempted through the...

Bucharest, the capital of Romania with about 2.5 million inhabitants, is frequently struck by intense, damaging earthquakes (2–3 events per century). The Collaborative Research Center 461 (CRC-461) entitled: “Strong Earthquakes - a Challenge of Geosciences and Civil Engineering” was established in July 1996 and ended in December 2007, but some proj...

REFMC 1929 - 2012 (Romanian Earthquake Focal Mechanism Catalogue) was compiled by Mircea Radulian, Andrei Bălă and Dragoș Toma-Dănilă from the National Institute for Earth Physics (INFP), Romania (http://www.infp.ro/) and comprises of earthquakes in Romania, in the 1929 - 2012 period, for which we were able to compute or retrieve focal mechanism pa...

Analyzing the partitioning of stress and deformation in active orogenic settings is of fundamental importance for understanding the mechanisms driving the geodynamic evolution and seismicity, particularly in complex orogenic settings. In this respect, a quantitative understanding is obtained by coupling the large-scale geodynamic evolution with par...

The studies for Recent Crustal Movements by the aid of space geodesy techniques are integrated into the researches on the Earth’s crust dynamics, as a reflection of the complex geodynamic phenomena that occur in the crust and in the subcrustal lithosphere. In addition to the fundamental nature, the research in this field presents a practical charac...

Fault plane solutions for earthquakes recorded in Romania (1929–2012) are analysed on three depth levels: crust (0–50 km), upper (50–110 km) and lower segment (110–201 km). For the Vrancea intermediate-depth source reverse faulting is predominant. However, local-scale variations occur at the upper and lower limits of the active volume: normal fault...

The purpose of this paper is to present the most comprehensive catalogue of focal mechanisms for Romanian earthquakes which occurred between 1929 and 2000 in the Carpathian Orogen, the Moesian and Moldavian Platforms, and the Transylvanian Basin. The present catalogue (REFMC) is a first step toward creating a centralized and continuous database of...

Earthquake mechanism information is fundamental to determine the stress field and to define seismogenic zones. At the same time, it is a basic input to compute seismic hazard by deterministic approach. The present paper extends the catalogue of the fault plane solutions for the earthquakes in Romania, previously completed until 1997, for 1998-2012...

Strong motion data are essential for seismic hazard assessment. To correctly understand and use this kind of data is necessary to have a good knowledge of local site conditions. Romania has one of the largest strong motion networks in Europe with 134 real-time stations. In this work, we aim to do a comprehensive site characterization for eight of t...

Earthquake mechanism information is fundamental to determine the stress field and to define seismogenic zones. At the same time, it is a basic input to compute seismic hazard by deterministic approach. The present paper extends the catalogue of the fault plane solutions for the earthquakes in Romania, previously completed until 1997, for 1998-2012...

Earthquake mechanism and fault plane solution information is fundamental to determine the stress field and to define seismogenic and active tectonic zones. At the same time, it is a basic input to compute seismic hazard by deterministic approach. The purpose of this paper is to update the catalogue of the fault plane solutions for Romanian earthqua...

Earthquake mechanism information is fundamental to determine the stress field and to define seismogenic zones. At the same time, it is a basic input to compute seismic hazard by deterministic approach. The present paper extends the catalogue of the fault plane solutions for the earthquakes in Romania, previously completed until 1997, for 1998 – 201...

Strong motion data are essential for seismic hazard assessment. To correctly understand and use this kind of data is necessary to have a good knowledge of local site conditions. Romania has one of the largest strong motion networks in Europe with 134 real-time stations. In this work, we aim to do a comprehensive site characterization for eight of t...

First results about cmstal models were obtained from various geophysical and seismological methods applied in Romania in the last part of XX centmy. A thorough interpretation of these data lead to the firs:t paitial models of cmstal stm cture in the western pa1t of Romania. In the first years after 2000 two regional seismic refraction lines were pe...

Tectonic of Romania includes both pre-alpine platforms and Alpine orogenic structures. The pre-alpine platforms are: Eastern European Platform, with its western margin in Romania—Moldavian platform; Scythian platform; Moesian platform.

Abstract Earthquake mechanism and fault plane solution information is fundamental to determine the stress field and to define seismogenic and active tectonic zones. At the same time, it is a basic input to compute seismic hazard by deterministic approach. The purpose of this paper is to update the catalogue of the fault plane solutions for Romanian...

In the years 1999 - 2000 two regional seismic refraction lines were performed within a close cooperation with German partners from University of Karlsruhe. One of these lines is Vrancea 2001, with 420 km in length, almost half of them recorded in Transylvanian Basin. The structure of the crust along the seismic line revealed a very complicated crus...

Earthquake mechanism and fault plane solution information is fundamental to determine the stress field and to define seismogenic zones and it is a basic input to compute seismic hazard by deterministic approach. The purpose of this paper is to update the catalogue of the fault plane solutions for Romanian earthquakes for the time interval 1998 - 20...

First results about crustal models resulted from various geophysical and seismological methods applied in Romania in the last part of XX century. A thorough interpretation of this data leads to the first partial models of crustal structure in the western part of Romania. In the first years after 2000 two regional seismic refraction lines were perfo...

Besides the intermediate depth earthquakes (Mw>7.0), in the SE Carpathians and its foreland a crustal seismicity (Mw<=5.6) is as well present. A correlation of the crustal hypocenter distribution with the deep structure displayed by the deep seismic lines is done. Some deep crustal faults extended down to the upper mantle are found out both in the...

Seismicity in western part of Romania is the result of tectonic evolution, which created a fragmented structure at the crystalline basement level, with blocks that have suffered differential movements due to general tectonic stress in the area, and due to secondary factors such as erosion or lateral variations in density. Some of the faults formed...

A joint inversion method of receiver function and Rayleigh wave dispersion is employed in order to derive the 1D seismic velocity models for several seismic station locations in western part of Romania. The study use new data emerged from permanent network of broadband stations in Romania, as well as data from temporary networks established during...

Moesian Platform is an old massif in the SE Europe bordered to the north and west by the South Carpathians, to the south by the Balkans, to the east by the Black Sea and to the NE by the North Dobrogean Orogen and Scythian Platform. In the Romanian sector, placed north of the Danube river topography of platform shows elevations of 100 - 200 m. Bas...

As a result of the continuous development in the last ten years of the network of the permanent broadband stations in Romania, valuable data for seismicity and crustal structure studies is now available, especially for the western part. Complementary to this national dataset, maintained and developed in the National Institute for Earth Physics, new...

Bucharest is among the European capitals most vulnerable to earthquakes. Although located at a relatively large epicentral distance (about 140–160 km) from Vrancea area, Bucharest has suffered much destruction and loss of life during great Vrancea earthquakes. In the last century, November 10th, 1940 earthquake (Mw = 7.7) caused the completely coll...

Different studies focused on the Vrancea subcrustal source of earthquakes pointed out the strong lateral inhomogeneous distribution of the seismic radiation. This implies characteristic macroseismic distributions, extremely elongated along NE-SW direction, and sharply restraint toward NW and SE. The fault plane solutions of most Vrancea earthquakes...

The most significant seismicity in Romania is located in a relatively small area – the Vrancea seismogenic zone, where 2–3 intermediate depth strong earthquakes (Mw > 7.0) occur in a century. Although the crustal seismicity is dispersed in several zones of country, only in a few areas the observed magnitudes exceeded Mw = 6.0. Nevertheless some cru...

Different studies focused on the Vrancea subcrustal source of earthquakes pointed out the strong lateral inhomogeneous distribution of the seismic radiation. This implies characteristic macroseismic distributions, extremely elongated along NE-SW direction, and sharply restraint toward NW and SE. Many authors ascribed this particular radiation patte...

The most significant seismicity in Romania is located in a relatively small area-the Vrancea seismogenic zone, where 2-3 intermediate depth strong earthquakes (Mw>7.0) occur in a century. Although the crustal seismicity is dispersed in several zones of country, only in a few areas the observed magnitudes exceeded Mw=6.0. Nevertheless some crustal e...

As a result of the deployment of the permanent Romanian broadband stations in the last 10 years, valuable data for seismicity and crustal structure studies in Romania has become available. Complementary to this dataset, during a joint project between University of Leeds, UK and National Institute for Earth Physics, Romania (South Carpathian Project...

The evaluation of seismic hazard and mitigation of the seismic risk is one of the permanent and urgent problems facing the Romanian society, equally implying work of seismologists, geologists and engineers. Significant efforts were made to predict the peak spectral amplification values values of the strong motion in Bucharest, the capital city. At...

Bucharest, the capital city of Romania, with more than 2 million inhabitants, is considered as a natural disaster hotspot by a recent global study of the World Bank and the Columbia University (Dilley M et al. Natural disaster hotspots: a global risk analysis. International Bank for Reconstruction and Development/The World Bank and Columbia Univers...

ABSTRACT The evaluation of seismic hazard and mitigation of the seismic risk is one of the permanent and urgent problems facing the Romanian society, equally implying work of seismologists, geologists and engineers. Significant efforts were made to predict the peak values and spectral characteristics of the strong motion in large urban areas, like...

Within the NATO Science for Peace Project 981882 “Site-effect analyses for the earthquake-endangered metropolis Bucharest, Romania” we obtain a unique, homogeneous dataset of seismic, soil-mechanic and elasto-dynamic parameters. Ten 50 m deep boreholes are drilled in the metropolitan area of Bucharest in order to obtain cores for dynamic tests and...

Abstract. Ten 50 m deep boreholes are drilled in the metropolitan area of Bucharest in order to obtain a unique, homogeneous dataset of seismic, soil-mechanic and elasto-dynamic parameters. Cores for dynamic tests were extracted and vertical seismic profiles were performed to obtain an updated site amplification model related to earthquakes waves....

Bucharest, the capital of Romania, with more than 2 million inhabitants, is considered after Istanbul the second-most earthquake-endangered metropolis in Europe. It is identified as a natural disaster hotspot by a recent global study of the World Bank and the Columbia University (Dilley et al., 2005). Four major earthquakes with moment-magnitudes b...

A new crustal model for the central and north-eastern part of Romania is relying on the largest database available at this moment. In comparison with previous crustal models the new model takes into account all known data: old and new seismic refraction data, deep seismic reflection data and seismology data recorded by the broadband stations belong...

The local surface geology, the soil behaviour as well as the local hydrogeological factors have a well-known influence upon the characteristics of the earthquake ground motion and the corresponding site effects. The geological and hydrogeological setting in Bucharest, the capital of Romania, as well as relative short recurrence intervals of strong...

The purpose of our study is to investigate the ground motion characteristics in 15 sites located in the Eastern part of Romania by applying the H/V spectral ratio method to the data (S and coda waves) recorded during the CALIXTO'99 tomography experiment. The results show no significant differences as regarding the resonant frequencies of the spectr...

Within the NATO Science for Peace Project 981882 "Site-effect analyses for the earthquake-endangered metropolis Bucharest, Romania" we obtain a unique, homogeneous dataset of seismic, soil-mechanic and elasto-dynamic parameters. Ten 50 m deep boreholes are drilled in the metropolitan area of Bucharest in order to obtain cores for dynamic tests and...

In seismic microzonation we want to display the variation in seismic response of the subsurface and subsequently determine where the soil is being amplified to a level that may damage existing buildings or other structures. Frequently peak ground acceleration (PGA) is used to determine the maximum horizontal forces that can be expected. The method...

Moesian Platform is an old massif in the SE Europe bordered to the N and W by the South Carpathians, to the S of the Balkans, to the E by the Black Sea and to the NE by the North Dobrogean Orogen and Scythian Platform. In the Romanian sector, to the N of the Danube river, the topography of platform shows elevations rarely exceeding 200 m. Basement...

Bucharest, the capital of Romania, with approximately 2.5 million inhabitants, is considered after Istanbul the second-most earthquake-endangered metropolis in Europe. It is identified as a natural disaster hotspot by a global study of the World Bank and the Columbia University (Dilley et al., 2005). Four major earthquakes with moment-magnitudes be...

Within the NATO-funded Science for Peace Project 981882 "Site-effect analyses for the earthquake-endangered metropolis Bucharest, Romania" was obtained a complete and homogeneous dataset of soil-mechanic and elasto-dynamic parameters. Ten 50 m deep boreholes were drilled in the metropolitan area of Bucharest in order to obtain the necessary data (d...

In seismic microzonation we want to display the variation in seismic response of the subsurface and subsequently determine where the soil is being amplified to a level that may damage existing buildings. Although is not always adequate, frequently peak ground acceleration (PGA)is used to determine the maximum horizontal forces that can be expected....

Bucharest is one of the cities most affected by earthquakes in Europe. Situated at 150–170 km distance from Vrancea epicentral zone, Bucharest had suffered many damages due to high energy Vrancea intermediate-depth earthquakes. For example, the 4 March 1977 event produced the collapse of 32 buildings with 8–12 levels, while more than 150 old buildi...

Within the NATO Science for Peace Project 981882 “Site-effect analyses for the earthquake-endangered metropolis Bucharest, Romania” we determined a complete and homogeneous dataset of seismic, soil-mechanic and elasto-dynamic parameters. Ten 50 m deep boreholes were drilled in the metropolitan area of Bucharest in order to recover cores for dynamic...

In seismic microzonation we want to display the variation in seismic response of the subsurface and subsequently determine where the soil is being amplified to a level that may damage existing buildings or other structures. Frequently peak ground acceleration (PGA) is used to determine the maximum horizontal forces that can be expected. The method...

Introduction Within the NATO Science for Peace Project 981882 “Site-effect analyses for the earthquake- endangered metropolis Bucharest, Romania” we determined a unique, homogeneous dataset of seismic, soil-mechanic and elasto-dynamic parameters. Ten 50 m deep boreholes were drilled in the metropolitan area of Bucharest in order to recover cores fo...

Processing techniques were applied to seismic data acquired by reflection methods. The seismic methods are efficient research methods for civil engineering and environmental geology, which invite to develop specific methodologies. Therefore, soft-programs for processing data collected with refraction seismic techniques (based on head and transmitte...

Bucharest is one of the most affected cities by earthquakes in Europe. Situated at 150-170 km distance from the Vrancea epicentral zone, Bucharest has suffered many damages due to high energy Vrancea intermediate-depth earthquakes. For example, the 4 March 1977 event produced the collapse of 32 buildings with 8-12 levels, while more than 150 old bu...