Earthquake mechanism and characterization of seismogenic zones in south-eastern part of Romania

Mircea Radulian, Andrei Bala, Emilia Popescu, Dragos Toma-Danila

Abstract


Earthquake mechanism information is fundamental to determine the stress field and to define seismogenic zones. At the same time, it is a basic input to compute seismic hazard by deterministic approach. The present paper extends the catalogue of the fault plane solutions for the earthquakes in Romania, previously completed until 1997, for 1998 – 2012 time interval. The catalogue is limited geographically to the Carpathians Orogeny and extra-Carpathians area located in the south-eastern part of Romania because similar investigations cover the rest of the country. The catalogue comprises 259 intermediate-depth seismic events and 90 crustal seismic events, recorded in the considered time interval with acceptably constrained fault plane solutions. We use specific graphical tools in order to emphasize statistically representative features of the stress field as coming out from our results. The fault plane solutions of the Vrancea earthquakes generated in a confined sinking plate in the mantle reflect the dominant geodynamic process in the study region. The typical features revealed by all the previous studies on the subcrustal seismic activity (predominant dip-slip, reverse faulting, characterizing both the weak and strong earthquakes) are reproduced as well by our investigation. As concerns the earthquake activity in the crust, a few new refined aspects are highlighted in the present work:  (1) a deficit of the strike-slip component over the entire Carpathians foredeep area, (2) different stress field pattern in the Făgăraş – Câmpulung zone as compared with the Moesian Platform and Pre-Dobrogean and Bârlad Depressions, (3) a larger range for the dip angle of the nodal planes in the Vrancea subcrustal source, ~ 400 -700 against ~ 700, as commonly considered.

Keywords


earthquake mechanism, seismogenic zones, fault plane solution catalogue

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References


DOI: https://doi.org/10.4401/ag-7443


 

Published by INGV, Istituto Nazionale di Geofisica e Vulcanologia - ISSN:  2037-416X