Scholarly record

CATALOG OF FOCAL MECHANISMS FOR VRANCEA (ROMANIA) INTERMEDIATE DEPTH EARTHQUAKES (2005-2017)

Phd. Craiu Andreea, Phd. Craiu Marius, St. Mihai Marius, Phd. St. Diaconescu Mihail, Phd. Ghita Cristian

Abstract

The Vrancea area, is known as a zone with intense and persistent crustal and intermediate seismic activity. The intermediate depth seismicity is concentrated in a high-velocity volume, an almost vertical body in fact a sinking lithosphere not completely detached, in the depth range from about 60 to 200 km. The epicentral zone is situated in an area of about 40 пїЅ 84 km2. The present tectonic of the Vrancea area is a result of a former subduction of oceanic lithosphere, followed by a continental collision and slab roll back or a delamination. The seismogenic process from Vrancea area remains far from being fully understood. The extension and upgrade of the National Seismic Network in last years has allowed us to detect and record a larger number of seismic events all over the country. Simultaneously the data quality has been improved which lead to a better event location, and fault plane solutions, even for a low magnitude events. Using the method developed by [1], termed FOCMEC method, implemented in SEISAN software [2], we obtain focal mechanisms for intermediate depth earthquakes that occurred in the Vrancea region from 2005 to 2017. Using the P-wave first motion polarities, we determine mechanisms for more than 300 earthquakes, with magnitude between 3.5?-ML?5.5 and analyze the statistical features of the whole catalog. The dominant style of faulting for Vrancea intermediate depth earthquakes presents a predominant reverse faulting, mechanism which indicates a predominant compressional stress field, with two main earthquakes categories: first one with the nodal planes oriented NE-SW parallel with the Carpathian Arc and the second one with the nodal planes oriented NW-SE perpendicular on the Carpathian Arc.

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