Abstract. The analysis of time-clustering behaviour of the sub-crustal seismicity (depth larger than 60 km) of the Vrancea region has been performed. The time span of the analyzed catalogue is from 1978 to 2008, and only the events with a magnitude of M w ≥ 3 have been considered. The analysis, carried out on the full and aftershock-depleted catalogues, was performed using the Allan Factor (AF) that allows the identificatiion and quantification of correlated temporal structures in temporal point processes. Our results, whose significance was analysed by means of two methods of generation of surrogate series, reveal the presence of time-clustering behaviour in the temporal distribution of seismicity data of the full catalogue. The analysis performed on the aftershock-depleted catalogue indicates that the timeclustering is associated mainly to the aftershocks generated by the two largest events occurred on 30 August 1986 (M w = 7.1) and 30 May 1990 (M w = 6.9).

Abstract. The crustal and sub-crustal seismicity that occurred in the Vrancea area from 1978 to 2008 is investigated. Due to quarry blast contamination, the analysis of the crustal seismicity was restricted to events that occurred between 20 km and 60 km, considering sub-crustal events as all those that occurred at depths larger than 60 km. The completeness magnitude was estimated between 2.3 and 2.5 for the crustal seismicity and between 2.9 and 3.1 for the sub-crustal one. The Gutenberg-Richter b-values show clear differences between crustal and sub-crustal seismicity, with values around 0.9 and 1.3-1.4, respectively. The analysis performed in this study represents a preliminary issue for the seismic hazard assessment of surrounding regions like Moldova, for which the earthquakes generated in Vrancea represent an important threat.

No abstract

No abstract

1269 the true structure of the system from the observed data. The array of seismic data is analyzed, consisting of values of 17 parameters characterizing the seismicity of the Vrancea source: MSK -intensity at the epicenter; Mw -moment magnitude; R-is the hypocentral distance; Az -azimuth to the most distant point; NP 1stk -the direction of the nodal plane 1; NP 1dp is the angle of incidence of the nodal plane 1; NP 1slip -offset of the nodal plane 1; NP 2stk -the direction of the nodal plane 2; NP 2dp is the angle of incidence of the nodal plane 2; NP2 slip -shift of the nodal plane 2; P az -azimuth of the compression axis; P pl is the angle of the compression axis; B az is the azimuth of the neutral axis B pl is the angle of the neutral axis; T az -azimuth of the axis of stretching; T pl is the angle of the stretching axis.Modern models of the Earth's structure and theories explaining the occurrence of earthquakes are based on indirect data, mainly on seismic observations. The main purpose of geophysical research is to solve the inverse problem, i.e. determination of the structure of the environment from observations of the characteristics of physical fields. The attenuation of the intensity of seismic effects is one of the factors determining the quality of seismic hazard analysis. The characteristics of the seismic impact of each earthquake are determined by its characteristics such as tectonics (tectonic structure of the region), focal depth, mechanism, focal geometry, direction and course of the process of fracturing of rocks and other parameters. The picture of the macroseismic field is a reflection of the influence of all these factors, and local geological features on the manifestation of the seismic effect at the points of the day surface. One of the significant factors determining the quality of seismic hazard analysis is the seismicity model of the earthquake zone. Seismicity is the susceptibility of the Earth or individual territories to earthquakes, which is a reflection of the geological processes occurring in the earth's interior, and occur in areas of the Earth that are different in structure and nature of geological development. Seismicity is characterized by: 1. Earthquake frequency 2. Statistical distribution of the force of shocks (magnitudes), 3. Spatial distribution of foci, 4. Macroseismic observations of strong seismic events (seismic intensity, damage pattern).In the study of seismicity, we are dealing with a seismic process occurring in time and space, and many of the tasks of seismology are associated with the ability to calculate the probabilities of some events associated with the seismic process and the determination of their probabilistic structure. Seismology is concerned with the study of earthquakes and related phenomena. The main task of seismology is to learn how to predict the strength, time and place of occurrence of earthquakes. The model, which covers various forms of dependence between events, is a real reflection of reality, but this leads to great difficulties in studyi...