Amplitude domain analysis for the 30 August 1986 Vrancea intermediate earthquake

The amplitude domain analysis applied to the major Vrancea (Romania) earthquake of 30 August 1986 leads to the determination of some parameters characterizing the amplitude and the time duration of the signal.Digital three-component acceleration data, obtained at 10 Romanian seismic stations with epicentral distances between 40 and 200 km, are used. The results are compared with those obtained by Schenk for strong Californian earthquakes.Paper presented in the 21st General Assembly of the European Seismological Commission, Sofia, 1988.     

Empirical relationships between macroseimic intensity and instrumental ground motion parameters for the intermediate-depth earthquakes of Vrancea region,Romania

Natural Hazards - Empirical relationships between MSK macroseismic intensity and several engineering ground motion parameters are developed using the macroseismic and instrumental data available...     

Waveform inversion of weak vrancea (Romania) earthquakes

Summary The inversion of high-frequency seismograms is performed to retrieve source mechanisms, hypocentral depths and source time functions of two weak Vrancea earthquakes (M_L=3.3), one that occurred in the crust, the other in the lithospheric part of the mantle. The digital waveforms recorded by the local Romanian network are used. Synthetic seismograms are computed by the modal summation method, using the point source approximation, for horizontally layered anelastic media. For each source-to-station path a different structural model is adopted which represents the best 1-D approximation of the medium in this azimuth. Thus, lateral inhomogeneities are taken into account in a simplified way. The source is described by the full moment tensor, allowing both deviatoric and volumetric components to be resolved.Although the structural models are simplified for the range of epicentral distances (15<<<170 km) considered, we find that the fit between the synthetic and observed seismograms is satisfactory for frequencies less than a few Hz. The few P-wave polarities available are not sufficient to determine a reliable source mechanism by standard methods, while the waveform inversion allows us to retrieve source mechanisms that are stable with respect to different boundary conditions and in good agreement with the observed polarities. The source time function is the less stable inverted parameter, being the most influenced by the simplification of the structural models.     

Statistical Models of the Seismicity of the Vrancea Region, Romania

A parameterization derived from the Weibull distribution is used to model the seismic activity of the Vrancea region.The analysis of 498 crustal earthquakes with local magnitudes greater than 2.0, and 1377 subcrustal events with local magnitudes greater than 2.5 emphasizes that the shallow sequences show a strong clustering tendency, while the intermediate depth mainshock sequences are modeled by a completely random pattern in space and time. These results are not influenced by the magnitude threshold and the width of the time window.The difference between the seismicity patterns in the crust and in the subcrustal zone correlates with the difference between the stress field within these two regions.