Nikolai Dobrev

• Professor
• Bulgarian Academy of Sciences

With this study, we are launching a project "Geological risk assessment on rock cultural monuments on the territory of the Eastern Rhodopes" supported by the Bulgarian National Science Fund (2025–2027). The project aims to develop a methodology for assessing the geological risks threatening the rock cultural monuments in the Eastern Rhodopes, Bulga...

The present study examines the change in landslide susceptibility under climate change conditions. The Landslide Susceptibility Index for the territory of Bulgaria was determined using the Mora and Vahrson method, based on the weighted assessment of various adverse conditions and destabilizing factors on slope stability. The input data include prec...

Sedimentological and geotechnical studies of Kaliakra Cape reveal the presence of specific sediments, carbonate tempestites, which are not found elsewhere in Northеastern Bulgaria. This fact allows a reinterpretation of the geological situation at the cape, suggesting a new structural model. The Sarmatian carbonate tempestites belong to a separate...

The aims of the publication are to provide a brief overview of research in Bulgaria to search for earthquake precursors related to gas/methane manifestations mainly in the water area in front of the Bulgarian coast and of known Bulgarian devices for monitoring gas emissions, as well as to propose a new monitoring site of underwater gas sources, and...

In recent years, society become much more interested in nature disasters that cause damage. The consequences of these destructive processes of a meteorological, hydrological and geological nature sometimes remain for years until the affected areas are recultivated, restored and recovered. These natural processes work together, often following each...

The medieval fortress Asenova Krepost (Asen’s Fortress) is built on a rocky massif of metamorphic rocks in south-central Bulgaria. The rock hill, on which the fortress was built, stands about 100 m above the Chepelarska River and the road Asenovgrad–Bachkovo Monastery, which passes at the foot of the slope. The slopes of the hill are steep and over...

As part of the Reimbursable Advisory Services on Accelerating Resilience to Disaster Risks, the World Bank worked with the Interior Ministry of Bulgaria to develop a proposal for the National Disaster Risk Profile of Bulgaria. The purpose of this document, which is the fourth technical annex to the proposal for the National Disaster Risk Profile, i...

The most northeastern part of the territory of Bulgaria is characterized by high seismicity. In 2019, archeoseismological studies of traces of strong earthquakes were carried out in the oldest architectural monument in Europe – Durankulak. There are reports of earthquakes in these places in the Middle Ages and in Аntiquity, but the data on the loca...

As a part of the Reimbursable Advisory Services on Accelerating Resilience to Disaster Risks, the World Bank has supported the Ministry of Interior, General Directorate for Fire Safety and Civil Protection in developing a proposal for the National Disaster Risk Profile of Bulgaria. The article presents initial data, methodologies, and results used...

Debris flow events periodically occur in the northern part of the Kresna Gorge, SW Bulgaria. Most of them damage the infrastructure and block the traffic along the National Route E79. In the present paper, we analyze the physical properties of the materials involved in debris flow transportation and sedimentation. Samples taken from events in 2017...

An assessment of the landslide risk (Rls) for the territory of Bulgaria by administrative districts has been made by combining the vulnerability (V) and landslide hazard (Hls) maps. Landslides are a significant part of geological hazards and are widespread throughout the country. In order to assess the landslide risk for the territory of Bulgaria,...

This article aims to present the results of geotechnical studies of the main rock complexes that compose the periphery of the Dobrudzha Plateau in the area from Cape Kaliakra to Cape Shabla (Bulgarian Black Sea Coast), directly related to the development of hazardous geological processes. Sediments of the Sarmatian age were studied: carbonate tempe...

This study presents the results of 227 tested specimens of the Sarmatian age taken from the rock complexes that build Kaliakra Cape: these are carbonate tempestites, as well as the limestones from the Karvuna Formation lying above them. Sedimentological and geotechnical tests have been performed. The micropetrographic analysis of the carbonate temp...

The article presents the results of the landslide mapping in the area of the town of Polski Trambesh, central Northern Bulgaria. A total of 37 new landslides have been described, which have not been included in the landslide register so far. Landslides are classified by area, type and activity. Their location is mapped in a GIS environment.

In October 2019, a 3D extensometer was installed to monitor slow landslide movements, affecting the slope of Cape Emine north of the lighthouse. For almost 2 years of observations, a tendency of shrinkage of the zone as a result of lateral pressure from the southern landslide was established. The movements are divided into two stages: the first – u...

We propose a new possible earthquake precursor, a coastal water jet originating from shallow water gas seeps and colored by sediments, lifted from increased gas seeps emissions, preceding some earthquakes with offshore epicenters along the Bulgarian Black Sea coast and M ≥ 3. The new possible earthquake precursor is site specific and may be observe...

Landslides are one of the most destructive natural processes. The Loire landslide seems to be the reference object in this regard, it has absorbed all the extreme features of landslide structures known in the Central Caucasus, but has not revealed the secrets of its static state, the determination of which is the most important task of the scientif...

Plastic soil-cement is a mixture of soil and cement prepared at water content W much higher than the optimum one Wopt, usually at or slightly above liquid limit WL of soil. Recently extensive investigations of plastic loess cement mixtures have been performed for assessment of various options for their using as engineering barriers in safe waste di...

Aim of this work is to show evidences for pre-earthquake processes and to set up earthquake forecasting experiments, based on two hypotheses: 1) extreme change of the activity of underwater methane seeps appears days before earthquakes; 2) effects from increase of shallow water seeps emissions are visible on satellite images.

The territory of Bulgaria has a high degree of landslide hazard with possible economic losses, social and environmental consequences. The Landslides are widespread throughout the country’s territory. They form the most serious part of the geological hazard in Bulgaria. The main factors for landslide activity (rainfall, impact of surface and ground...

The Bulgarian Black Sea coast is a region where a considerable part of the deep complex landslides in the country are distributed. More than 200 landslides affect only urban areas, resorts and villa zones. Depending on the depth range, geological and tectonical structure and the engineering geological properties of the geological units, the Bulgari...

This article presents the initial results of the 3D monitoring of West Pirin Fault in the area of the village of Brezhani, SW Bulgaria. The monitoring equipment—extensometer TM71 was installed in August 2013. The data obtained from the observations until August 2018 were processed. The results show four stages in the dynamics of this part of the fa...

Two sections from Kaliakra Cape composed of tempestites (carbonate con-glomerates and limestones) have been sedimentologically and geotechnically investigated. Probably, these storm deposits were accumulated between the late Bessarabian and early Khersonian (Sarmatian). The lack of macro-and mi-crofossils and, at the same time, the high carbonate c...

В редица публикации, както и в изявления по медиите видни чужди и наши сеизмолози признават, че сеизмологията все още не разполага със сигурни методи и технически средства за краткосрочно прогнозиране на земетресения. Излагат се редица факти, събития, обстоятелства и съображения, които мотивират необходимостта от незабавно експериментиране на бълга...

The NATIONAL GEOINFORMATION CENTER (NGIC) is a newly established scientific infrastructure for cooperation and integration of human resources, informational products and data from monitoring networks and observatories, their complex analysis and implementation into services to the community. It is part of the National road map for scientific infras...

The only early medieval rock bas-relief in Europe Madara Horseman is included in UNESCO World Heritage List. This article presents the results from an in situ monitoring of microdisplacements across fissure forming the Golyamata Tsepnatina Cave located at the edge of Madara Plateau above the Horseman, NE Bulgaria. Additionally, we studied movements...

Rock collapses phenomena are one of the main processes constituting the geological hazard. Most commonly, the concept of "collapses" covers several different types of rock deformations: rockfall (linear and wedge-shaped), rock toppling, etc. It is difficult to predict the exact moment of the occurrence of a rock collapse. For this reason, it is nec...

This article presents the initial results of the 3D monitoring of West Pirin Fault in the area of the village of Brezhani, SW Bulgaria. The monitoring equipment – extensometer TM71 was installed in August 2013. The data obtained from the observations until November 2018 were processed. The results show 5 stages in the dynamics of this part of the f...

The territory of Bulgaria is at risk of a number of unfavorable and destructive geological processes and phenomena constituting the geological hazard. The generally high hazard degree necessitates analyzing, evaluation and mapping of the geological hazard and risk processes. Evaluation and mapping of geological risk is the final stage of a long-las...

The north-western and western coast of the Black Sea, corresponding to Romania and Bulgaria, is subject of crustal deformations due to remote effects produced by geological processes ran at planetary (e.g. plate tectonics in the Atlantic and Eastern Mediterranean-Anatolia realms) and regional (e.g. the tectonic coupling of the Black Sea basin and V...

Mapping the landslides is one of the main activities in the overall spectrum of geological hazards and geological risk. Landslides form the most serious part of the geological hazard in Bulgaria after the earthquakes. They are widespread in the all country’s territory. All known landslide types of internationally accepted classification of Varnes (...

The information available of the carried out geological and geomorphological, geophysical and geodetic research on Bulgarian Black Sea coast and adjacent aquatory is not possible to identify indications of forthcoming seismic manifestations. This question remains unresolved worldwide, despite centuries of accumulated experience and the latest geoph...

1 Институт по океанология, БАН, ул. " Първи май " 40, ПК 152, 9000 Варна 2 Геологически институт " Стр. Димитров " , БАН, ул. " Акад. Г. Бончев " , бл. 24, Abstract. The present study is focused on the development of geological setting under the erosional basis of the Early Holocene regression in the upper Northwestern Black Sea continental slope....

Landslides are a major hazard causing human and large economic losses worldwide. However, the quantification of fatalities and casualties is highly underestimated and incomplete, thus, the estimation of landslide risk is rather ambitious. Hence, a spatio-temporal distribution of deadly landslides is presented for 27 European countries over the last...

Landslides are a major hazard causing human and large economic losses worldwide. However, the quantification of fatalities and casualties is highly underestimated and incomplete, thus, the estimation of landslide risk is rather ambitious. Hence, a spatio-temporal distribution of deadly landslides is presented for 27 European countries over the last...

In this article detailed sedimentological and petrographical analyses on the upper part of the core EuxRo03-3 were carried out and the regressive-transgressive events were determined. At the sapropel base in the core EuxRo 03-3 five white aragonite laminae were described. The composition of the first two laminae was determined. They are composed of...

An overview on the main hazardous geological processes endangered the Romanian-Bulgarian Black Sea coast with emphasize on hazards related to Bulgarian side, and goals and objectives of the Cross border project MARINGEOHAZARD whose purpose is to create key core components of a joint early warning monitoring system approved on both countries. The ba...

Кално-каменните порои в северната част на Кресненското дефиле: характеристика на зоната на подхранване и свойства на изграждащите я материали

The Oryahovo town is located at high Danube coast, and has been affected by landslide. Many houses and streets in the town are heavily deformed by continually ongoing landslide movements. The slope is affected by deep-seated landslide from translational type, which is in stabilized or in condition of slow creep. In the landslide body are created sh...

The present article is a part of the implementation of the task for standardization of distinct types of the Upper Pleistocene-Holocene sediments in the Black Sea Basin. Detailed sedimentological analysis for the upper part of the core was carried out as the regressive-transgressive events were determined. It is proved that the lowest aragonite lay...

Dobrudzha coal deposit is located in a tectonically disturbed zone in north-eastern Bulgaria. It has not been exploited till now due to the great depth of occurrence (1200 ÷ 1400 m) and very complicated geological and hydro geological conditions. Several storey arranged aquifers are discovered in the region. Each of them has a specific chemical com...

The present paper aims to analyse and to discuss the state of landslide problems in Bulgaria. It separates the main factors of instability of slopes Bulgarian landslides: tectonic movements, earthquakes, erosion, abrasion, surface water and groundwater, precipitation and human impact. Landslides are concentrated in certain regions: Black Sea Coast,...

The Northern Bulgarian Black Sea coast is about 100 km strip that almost along its entire length is affected by landslides. Тhese landslides are irregularly distributed in four landslide areas. Most of the landslides are complex and deep-seated. The present article analyses the old and recent sliding phenomena along the coastal zone in this part of...

Continuous refreshment of the database for historical earthquakes in a certain region is a task of great importance. Peculiarities of historic and cultural development of diverse territories over present-day Bulgarian lands are implied as determining factors. Documentary information sources are examined. Field inspection of archaeological sites in...

The general frame of the BG-ROM MARINEGEOHAZARDS project is considered. The main focus is on the rough data and information about the investigations related to the creation of the marine geo hazards early warning system. The target topics are on the earthquakes, landslides, tsunamis, floods and similar natural hazards. Maps and schemas about the ma...

The present paper concerns long-term 3D monitoring of active fault structures in the Krupnik-Kresna seismic zone, SW Bulgaria with the use of extensometers TM71. The purpose is to establish the real rates of fault movements in the most seismically active area in Bulgaria. Three points were installed (B6 on Krupnik Fault, and K5 and K12 on Struma Fa...

E. Àâðàìîâà-Òà÷åâà, Í. Äîáðåâ — Î ïðèëîæåíèè ìîíèòîðèíãîâûõ 3D ìåòîäîâ ê àêòèâ- íûì ðàçëîìàì è ãðàâèòàöèîííûì äâèæåíèÿì. Ðàáîòà ïîñâåùåíà ïðèëîæåíèþ ìåòîäîâ äëÿ îñóùåñòâåëåíèÿ 3D-ìîíèòîðèíãà ìåäëåííûõ îïîëçíåé è äâèæåíèé ïî ðàçëîìàì. Ñà- ìûìè ïðåäñòàâèòåëüíûìè ïðèìåðàìè ýòèõ ñòðóêòóð íà òåððèòîðèè Áîëãàðèè ÿâëÿþòñÿ: ãëóáîêîçàëåãàþùèå îïîëçíè "Òàóêë...

The necessity of contemporary assessment of the natural hazardous processes on the territory of Bulgaria leading to disastrous and catastrophic situations in a number of regions is motivated by their high activity resulting in destruction of building fund, infrastructure, historical

Long-term repeated measurements of microdisplacements in tectonic fault structures of various parts of Central Europe and the Balkan Mountains showed that displacement trends changed significantly at several points in the period from 1997 through 2000; afterward, long-term trends were restored. This phenomenon took place in the periods of strong (M...

We combined field mapping and structural analysis of Landsat imagery in order to identify active faults in the broader area of the Simitli graben and to the east towards the cities of Razlog and Bansko, in southwest Bulgaria. We mapped five large active fault segments with normal-slip kinematics and down-to-north displacement and three smaller, ant...

We combined field mapping and structural analysis of Landsat imagery in order to identify active faults in the broader area of the Simitli graben and to the east towards the cities of Razlog and Bansko, in southwest Bulgaria. We mapped five large active fault segments with normal-slip kinematics and down-to-north displacement and three smaller, ant...

The present paper shows the results of 3D monitoring with the use of extensometers TM71 performed in Bulgaria in the framework of COST Action 625. This research was performed in selected areas: Simitli graben that is the most seismoactive area in Bulgaria; Madara plateau - rock scarp with historical monument affected by rock toppling; East Rhodopes...

We combined field mapping and structural analysis of Landsat imagery in order to identify active faults in the broader area of the Simitli graben and to the east towards the cities of Razlog and Bansko, in southwest Bulgaria. We mapped five large active fault segments with normal-slip kinematics and down-to-north displacement and three smaller, ant...

A large impressive landslide occurred in 2001 at the General Geshevo Village area, East Rhodopes, SE Bulgaria. After the sliding, a system of preserved faults was observed in the area. The present paper relates the detailed study, mapping, selection and installation of movement monitoring site. Preliminary results establish displacements that could...

Long-term in situ monitoring of slow tectonic movements has been applied to a seismoactive region of SW Bulgaria, within the epicentral zone of one of the strongest earthquakes in Europe (4 April 1904, M=7.8). The region has been found the most seismoactive in Bulgaria being of interest to many scientists. Three spatial extensometers were installed...

Preservation of a historical bas-relief on a high rock face in a seismically active area in NE Bulgaria called for stability investigations including joint monitoring. Engineering geological investigations revealed structures liable to creep within the bedrock including joint deformations registered in spatial three components and angular deviation...

The complex investigations concern the determination and the study of the character of: recent Earth's crust vertical and horizontal movements (by using up-to-date geodetic and semigeodetic methods, including GPS technique}, seismotectonic conditions, tectonic stresses in the region and their analysis, and interpretation. Movements with normal and...

The slope processes affecting the peripheries of 3 plateaux in NE Bulgaria have been monitored since 1973. Established displacements described by the function x = f(t) show simultaneously a trend and a sinusoidal function of the displacements. An equation for analysis and prognostication of the monitored rock deformations has been deduced. This equ...

70% of Japan is mountains, and the land is surrounded in 30,000 km coastline. The geology belongs to the mobile belt, and there are many earthquakes and volcanoes. The climate be- longs to the monsoon, and the heavy rain frequently arises. Therefore, Japan has suffered many slope disasters every year. The number of slope disasters in Japan shows ab...

The rock bas-relief Madara Horseman is carved into limy sandstone on the main rockwall of the Madara Plateau in the 8th Century AC. The monument is included in the World Heritage List of UNESCO. The monument was subjected to the destructive effects of various natural processes throughout its 12 centuries of history, namely weathering, erosion, crac...