Seismic Hazard of Romania: Deterministic Approach

Abstract

The seismic hazard of Romania is estimated in terms of peak-ground motion valuesdisplacement, velocity, design ground acceleration (DGA) -computing complete synthetic seismograms, which are considered to be representative of the different seismogenic and structural zones of the country. The deterministic method addresses issues largely neglected in probabilistic hazard analysis, e.g., how crustal properties affect attenuation, since the ground motion parameters are not derived from overly simplified attenuation ''functions,'' but rather from synthetic time histories. The synthesis of the hazard is divided into two parts, one that of shallow-focus earthquakes, and the other, that of intermediate-focus events of the Vrancea region.The previous hazard maps of Romania completely ignore the seismic activity in the southeastern part of the country (due to the seismic source of Shabla zone). For the Vrancea intermediate-depth earthquakes, which control the seismic hazard level over most of the territory, the comparison of the numerical results with the historically-based intensity map show significant differences. They could be due to possible structural or source properties not captured by our modeling, or to differences in the distribution of damageable buildings over the territory (meaning that future earthquakes can be more spectacularly damaging in regions other than those regions experiencing damage in the past). Since the deterministic modeling is highly sensitive to the source and path effects, it can be used to improve the seismological parameters of the historical events.

Tectonic stress, seismicity, and seismic hazard in the southeastern Carpathians

“…To assess the seismic hazard in the SE-Carpathians, strong ground motion excitation and attenuation during the intermediate-depth Vrancea earthquakes were analyzed (Marza and Pantea 1994;Lungu et al 1995Lungu et al , 1999Ivan et al 1998;Oncescu et al 1999a;Moldovan et al 2000;Radulian et al 2000;Gusev et al 2002). The studies are based on the macroseismic data and the analog accelerograms of the large 1977, 1986, and 1990 Vrancea earthquakes (Lungu et al 1995;Oncescu et al 1999a).…”

Microzonation of Bucharest: State-of-the-Art

“…Vrancea is the main seismogenic zone of Romania and exhibits the following remarkable features: (a) highly restricted hypocentral area within 45°-46°N latitude and 26°-27°E longitude, at the SE corner of the strongly bent Carpathian arc; (b) shallow seismic activity -located mainly in the lower crust (h > 15 km) with small to moderate magnitudes; M L ¼ 5. 3 (1914) is the strongest crustal event ever recorded; (c) subcrustal seismicity, very well clustered in a focal volume confined between 60 and 180 km of depth, represents the major feature of Vrancea region; the persistent rate of occurrence amounts to 12-15 events monthly (M L ‡ 3); the corresponding epicentral area is limited to a rectangle of about 30 Â 70 km 2 NE-SW oriented that partly overlaps the epicentral area of the crustal events (RADULIAN et al, 2000b); maximum ground displacements up to 30 cm and peak accelerations on the order of 0.3 g were recorded in the area situated eastward and southward of the Carpathians arc (RADULIAN et al, 2000a); (d) the recurrence times estimated from the available catalogues are: 10 years for M w ‡ 6.5, 25 years for M w ‡ 7.0 and 50 years for M w ‡ 7.4 ; (e) the large earthquakes (instrumentally recorded) show a remarkably similar fault plane solution that typically has strike SW-NE (220°), dip 60°to 70°to the NW, and slip roughly 80°to 90° (RADULIAN et al, 2000b; the stress regime is clearly compressive; despite the similarity of the fault plane solutions, significant variations of the radiation pattern are noticeable, which reflect the dynamics of the rupture process (ONCESCU and BONJER, 1997); (f) the total seismic moment released by the last four strong events (1940, 1977, 1986 and 1990) is similar to a maximum possible Vrancea source of magnitude M w ¼ 8.0 which means an average amount of seismic moment released of 8 Â 10 20 Nm/yr ; according to ONCESCU and BONJER (1997) the sum amounts to 7:5 Â 10 20 Nm for a period of about 100 years; (g) the depth interval between 110 and 130 km is considered to be a candidate for the next strong Vrancea event since this remained unruptured during at least the last 150 years (ONCESCU and BONJER, 1997). Several geophysical models based either on subduction processes or on slide break-off and necking have been proposed to explain the amazingly confined Vrancea subcrustal seismicity (e.g., FUCHS et al, 1978;ONCESCU, 1984;TAVERA, 1991;GIRBACEA, and FRISH, 1998).…”

“…Statistics based on historical records indicate that about three destructive subcrustal earthquakes per century occur in Vrancea. They can produce peak ground displacement of about 30 cm and peak acceleration on the order of about 30% of the gravity acceleration, 0.3 g (RADULIAN et al, 2000a).…”

Synthetic Seismogram Based Deterministic Seismic Zoning for the Hungarian Part of the Pannonian Basin

“…All the seismogenic zones listed in Table 2 have been defined by the authors of this paper, except the zones number 13 and 14 which have been constructed by Romanian researchers (RADULIAN et al, 2000). …”