Abstract
Abstract. The crustal and sub-crustal seismicity that occurred in the Vrancea area from 1978 to 2008 is investigated. Due to quarry blast contamination, the analysis of the crustal seismicity was restricted to events that occurred between 20 km and 60 km, considering sub-crustal events as all those that occurred at depths larger than 60 km. The completeness magnitude was estimated between 2.3 and 2.5 for the crustal seismicity and between 2.9 and 3.1 for the sub-crustal one. The Gutenberg-Richter b-values show clear differences between crustal and sub-crustal seismicity, with values around 0.9 and 1.3–1.4, respectively. The analysis performed in this study represents a preliminary issue for the seismic hazard assessment of surrounding regions like Moldova, for which the earthquakes generated in Vrancea represent an important threat.
Highlights
Seismic hazard assessment depends mainly on earthquake catalogs
On the basis of the ROMPLUS catalog, 13 seismic active zones were identified in Romania (Marmureanu, 2009)
The crustal seismicity of the Vrancea area is due to a series of active faults that have caused a high degree of crust fracturing (Oncescu and Trifu, 1987), while sub-crustal earthquakes occur on a slab, partially or completely detached from the continental crust in a weak sinking process (Wenzel et al, 1999; Radulian et al, 1999)
Summary
Seismic hazard assessment depends mainly on earthquake catalogs. Several catalogs collect information on the Carpathian earthquakes: (i) the catalog of historical Romanian earthquakes, spanning over a millennium (984–1979) (Constantinescu and Mirza, 1980), provides 4 types of magnitudes, with minima ranging from 3 to 6. (ii) The Radu Catalog (Radu, 1994) consists of the historical earthquakes with level of intensity I0 > 6 and instrumental earthquakes with the level of M > 5.0. (iii) Catalog of micro- earthquakes of intermediate-depth Vrancea region (Trifu and Radulian, 1991) collects all the earthquakes of Vrancea during 1974– 1990, with minimum magnitude ML of 2.1. (iv) The catalog ROMPLUS (Oncescu et al, 1999) uses the seismic magnitude scale MW for all the historical and instrumentally recorded seismic events. The crustal seismicity of the Vrancea area is due to a series of active faults that have caused a high degree of crust fracturing (Oncescu and Trifu, 1987), while sub-crustal earthquakes occur on a slab, partially or completely detached from the continental crust in a weak sinking process (Wenzel et al, 1999; Radulian et al, 1999).
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