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, it is necessary to take into account not only all landslides for a given region, but also its vulnerability, and thus to assess the level of landslide risk for this region, Rls = f (V, Hls). Landslide risk is determined by a risk matrix, using selected indicators and weighting coefficient of vulnerability and landslide hazard. Assessing the vulnerability of a region subjected to geological hazards is a key component of risk assessment. These include the exposure of infrastructure, industrial facilities and production capacity, residential buildings, regional GDP per capita and potential for human disability (defined by population density in the district). The data used is combined to create a map showing the vulnerability of each administrative district. Indicators of population density, GDP, length of road and railway networks and number of residential buildings were used to assess the vulnerability. The landslide hazard in each administrative district is determined by the intensity of landslide processes in the district, depending on the level of their activity and the affected area. The normalized (distributed) hazard of landslides for an administrative region is given depending on the area of the given administrative region. Landslides are categorized as active, potential and stabilized. The results express the weighted average hazard. Landslide hazard is rated from 1 to 5, where 1 means no landslide hazard and 5 means that landslide hazard has a very high intensity (very high hazard). The high degree of landslide hazard in turn leads to possible economic losses, social and environmental consequences (landslide risk). The intensity (level) of landslide vulnerability, hazard and risk is assessed as very low, low, medium, high and very high, and is shown on the relevant maps.

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, historicalmonuments, land use disturbance and annihilation of areas, interrupting of communications, aggravation of ecological conditions, human health threats, social stress enhancement. The landslide manifestations displayed recently along the Black Sea coast and the Danubian riparian area, the Rhodopes and other parts of the country and their serious consequences confirm the long ago ascertained truth that the Bulgarian territory is characterized by a high degree of landslide hazard. The geological-tectonic conditions and the relief of the country determine the development of a large number of landslides on its territory. The many years of research and applied activities on landslides have led to the establishment of important relationships for their distribution, factors for origin and activation, mechanism and dynamics, etc. The origin and activation of landslides is a consequence of the influence of many factors — tectonic, seismic, geomorphologic, climatic and technogenic ones. A part of them act permanently, while others have short-term impact. Both separately and in combination they reduce slope stability and provoke the manifestation of big and destructive landslides. The impact of the destabilizing factors and the distribution of 403 landslides are analyzed in this work. Regions with different degree of landslide hazard have been distinguished. Diagrams are shown for the regional distribution and time of landslide display. The weighted effect of the destabilizing factors for slope stability formation is different. A part of them as the contemporary vertical movements and earthquakes are of regional importance, others act locally — erosion, abrasion, precipitation. The origin of the active landslides may be closely related to contemporary tectonic activity. The regional distribution of the landslides according to their volume shows that landslides with a volume up to 10 million m3 are the prevailing type in the country. The most numerous landslides in this group — about 50% of the total number — are observed along high Danubean Bank and Northern Black Sea coast, in the tectonically active grabens as Sofia, Pernik or Simitli and the landslides along some of the faults in the Strouma zone. The largest landslides with a volume of more than 100 million m3 are encountered along the Danubean Bank, the Northern Black Sea coast and in Rhodope Region.

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 deviations between joint faces. A distinct relationship between joint movement and individual earthquakes has been found and changes in deformation character have occurred in periods of increased seismicity. Temperature variations, and notably frost effects have been found to affect shallow joints. The paper describes a case in which relatively inexpensive monitoring has been successful in terms of interpretation of results.