A note on the depth recurrence and strain release of large Vrancea earthquakes

Oncescu, Mihnea Corneliu; Bonjer, K.‐P.

doi:10.1016/s0040-1951(96)00263-6

Cited by 125 publications

(77 citation statements)

References 13 publications

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“…List of earthquakes analyzed in this study. Earthquake parameters after Oncescu and Bonjer (1997). σ is static stress drop (bar): 1977 event after Tavera (1991), 1986 event after Oncescu (1987) and 1990 event after Trifu et al (1992).…”

Section: Fig 1 (A)mentioning

confidence: 99%

“…The fault plane solutions of the instrumentally recorded large earthquakes are remarkably similar. The fault planes typically strike SW-NE and dip either to the NW or to the SE (Oncescu and Bonjer, 1997;Sperner et al, 2001;Wenzel et al, 2002). In this paper we assume that the fault dip is to NW following closely the particular geometry of the foci distribution ( Fig.…”

Section: Introductionmentioning

confidence: 99%

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Vrancea slab earthquakes triggered by static stress transfer

Ganas

Grecu

Batsi

et al. 2010

Nat. Hazards Earth Syst. Sci.

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Abstract. The purpose of this paper is to study the interaction of the Vrancea seismic activity (Romania) in space as result of Coulomb, static stress transfer during M = 7+ events. In this area, three large events occurred in 1977, 1986 and 1990 at mid-lower, lithospheric depths and with similar focal mechanisms. Assuming elastic rheology for the deforming rocks it is suggested that frictional sliding on pre-existing fault produced the 1986 M = 7.1 event (depth 131 km), that was possibly triggered by the 1977 M = 7.4 event (depth 94 km). We calculated a static stress transfer of 0.52-0.78 bar to the hypocentre of the 1986 event. On the contrary, the occurrence of the 1990 event is uncertain: it is located inside the relaxed (shadow) zone of the combined 1977 and 1986 static stress field considering an azimuth for maximum compression of N307 • E. It follows that, the 1990 earthquake most likely represents an unbroken patch (asperity) of the 1977 rupture plane that failed due to loading. However, if a different compression azimuth is assumed (N323 • E) then the 1990 event was also possibly triggered by static stress transfer of the 1977 and 1986 events (combined). Our modeling is a first-order approximation of the kind of earthquake interaction we might expect at intermediate lithospheric depths (80-90 to 130-140 km). It is also suggested that static stress transfer may explain the clustering of Vrancea earthquakes in space by the rupturing of two (possibly three) NW-dipping major zones of weakness (faults) which accommodate the extension (vertical elongation) of the slab.

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Section: Fig 1 (A)mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Vrancea slab earthquakes triggered by static stress transfer

Ganas

Grecu

Batsi

et al. 2010

Nat. Hazards Earth Syst. Sci.

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“…Vrancea seismicity is further characterized by pronounced background activity which delineates the rupture area of the strong earthquakes (e.g. Oncescu and Bonjer, 1997).…”

Section: Vrancea Intermediate Depth Earthquake Zonementioning

confidence: 99%

“…Oncescu et al, 1999). In particular, Joint Hypocenter Determinations (JHD) showed that the Vrancea seismogenic zone has a two-dimensional geometry rather than a three-dimensional one (Oncescu, 1984;Oncescu and Trifu, 1987;Trifu et al, 1992;Oncescu and Bonjer, 1997). Recent analyses of the travel time data of the K2-network (Bonjer et al, 2000) reveal further details of the fine structure of the geometry of the Vrancea focal zone .…”

Section: Vrancea Intermediate Depth Earthquake Zonementioning

confidence: 99%

Probabilistic seismic hazard map for Romania as a basis for a new building code

Ardeleanu

Leydecker

Bonjer

et al. 2005

Nat. Hazards Earth Syst. Sci.

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Abstract.A seismic hazard map proposed as part of a new building code for Romania is presented here on basis of the recommendations in EUROCODE 8.Seismic source zones within an area of about 200 km around Romania were constructed considering seismicity, neotectonics and geological development. The probabilistic seismic hazard assessment in terms of intensities is performed following Cornell (1968) with the program EQRISK (see Mc Guire, 1976), modified by us for use of intensities.To cope with the irregular isoseismals of the Vrancea intermediate depth earthquakes a factor is introduced to the attenuation law (Kövesligethy, 1907). Using detailed macroseismic maps of three earthquakes is calculated by fitting the attenuation law to observed intensities, i.e. to local ground conditions. Strong local variation of is avoided by a gridding of 0.5 • in longitude and 0.25 • in latitude. The contribution of the Vrancea intermediate depth zone to the seismic hazard at each grid point is computed with the corresponding representative . A seismogenic depth of 120 km is assumed.The final seismic hazard is the combination of both contributions, of zones with crustal earthquakes and of the Vrancea intermediate depth earthquakes zone. Calculations are done for a recurrence period of 95, 475 and 10 000 years. All maps show the dominating effects of the intermediate depth earthquakes in the Vrancea zone, also for the capital Bucharest.

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“…According to a historical catalogue of Vrancea events, large intermediate-depth shocks with magnitudes M S >6.5 occur three to five times per century. In the XXth century, large events at depths of 70 to 170 km occurred in 1940 with moment magnitude M W =7.7, in 1977 M W =7.4, in 1986 M W =7.1, and in 1990 M W =6.9 [4].…”

Section: Seismicity and Geodynamics Of The Se-carpathiansmentioning

confidence: 99%

Modelling of Stress and Seismicity in the South-Eastern Carpathians

Ismail‐Zadeh

2003

Risk Science and Sustainability Science for Reduction of Risk and Sustainable Development of Society

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A note on the depth recurrence and strain release of large Vrancea earthquakes

Cited by 125 publications

References 13 publications

Vrancea slab earthquakes triggered by static stress transfer

Vrancea slab earthquakes triggered by static stress transfer

Probabilistic seismic hazard map for Romania as a basis for a new building code

Modelling of Stress and Seismicity in the South-Eastern Carpathians

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