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SEISMICITY ASSOCIATED TO THE INTRAMOESIAN FAULT: INFERENCES FROM REGIONAL TECTONICS AND GEODYNAMICS

Irina Stanciu

Abstract

The study is based on seismicity data analysis, using seismological data available from published local, regional and global earthquakes catalogues. Seismicity data for Romania, Bulgaria and the Western Black Sea have been compiled into a unique data-base and represented within a georeferenced framework. A large number of seismicity maps at various depths and depth intervals, as well as W-E, N-S and NE-SW in-depth seismicity graphs have been built. The regional structure of interest is the Intramoesian Fault (IMF), the study area being largely extended in order to better depict its geotectonic features. The Intramoesian Fault has been described as a NW-SE trans-crustal fault, crossing both the Romanian and Bulgarian territories, from underneath the Getic Nappe, across the Moesian Platform, up to the Black Sea shelf. The ?intramoesian? name given by M. Sandulescu (1984) was meant to illustrate the fault mostly accepted geotectonic characteristic: separating the Moesian Platform in two distinct tectonic domains, westward and eastward, with different basement petrographic facies and geological age. The crustal seismicity data on the Moesian Platform illustrates a NW-SE seismicity boundary trending between the South Carpathians and the Danube river, separating an eastern high seismicity compartment from a western low seismicity one. However, the western limit of high seismicity area does not overlap the geologically interpreted position of the Intramoesian Fault. The geometry of the tectonic contact, as illustrated by earthquakes hypocentres, suggests a soft collision between crustal tectonic blocks. When addressing the Intramoesian Fault, the analyzed seismicity data showed seismic events of low to moderate magnitude, difficult to be included in lineaments of active tectonics significance. However, there were found situations where such NW-SE trending lineaments with seismic epicenters indicate tectonic activity on segments of the Intramoesian Fault. The interpreted seismicity data may be related to movements along the Intramoesian Fault system, as GPS results on crustal deformations illustrated two main directions for its compartments: a SE oriented displacement of Eastern Moesia and a southward displacement of Western Moesia . Regional seismicity data suggest that tectonic activity may be also determined by displacements along NE-SW seismic lineaments when crossing the Intramoesian Fault.

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DOI resolver: doi.org/10.5593/sgem2019/1.1/s05.114

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