Satellite remote sensing data applied for seismic risk assessment of Vrancea region

The aim of this study is to present the results of the application of remote sensing techniques for seismic risk analysis, which estimate the geographic distribution, frequency, and intensity of seismic activity, without attempting to predict specific events. This method is based on the recognition of the active faults, which are defined as breaks along which movement has occured in Holocene time (past 11,000 years ). Remote sensing analysis and field studies of active faults can provide a geologic history that overcomes many of the shortcomings of instrumental and historic records. The majority of strong Romanian earthquakes has the origin in Vrancea region, a distinctive active zone of the Alpine orogenic belt placed at the Eastern Carpathians Are Bend with extensive macroseismic area. Many seismological researches revealed two kinds of mechanisms involved in the occurrence of intermediate earthquakes having a Vrancea focus : one has a NW-SE oriented compression az;ix ( the fault plane direction is NE-SW) while the other has a NE-SW orientated compresion axis ( the fault plane direction is NW-SE). Subduction of the Black Sea Sub-Plate under the Pannonian Plate produces faulting processes. The fault plane is oriented approximately parallel to the Carpathian Bend, i.e. NE-SW. The Black Sea Sub-Plate would have a NW displacement along "the markers" formed by the Moesian and Eurasian Sub-Plates admiting of another fault plane, oriented NW-SE, approximately perpendicular to the first. Landsat images are excellent for recognising the continuity and regional relationships of faults, but the spatial resolution is not so good to distinguish topographic features indicative of active faults. SAR ERS-1 data are more useful for this purpose. This also allows a more precise characterization of lineament structures, especially in cloud and soil covered areas, where the lack of data reduces the tectonic analysis. An on-going evaluation of all data will lead to a better understanding of the stress field which controlled the tectonic movements. The results obtained from the remotely sensed data have shown a good concordance with the available "in-situ" data implying that remote sensing techniques provide a means for locating, identifying and mapping certain terrain features and aspects of geologic structures. Further methodical work on Landsat TM and ERS-1 and ERS-2 SAR data will be useful to elaborate even physical parameters for the discrimination of different lithological units.