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In the region of the Carpathian-Pannonian Basin (44–50N; 13–28E) 81 earthquakes have moment magnitude (M w); 61 of them are crustal events (focal depth <65 km) while 20 earthquakes belong to the intermediate focal depth region of the Vrancea (Romania) zone. For crustal events the regression of moment magnitude (M w) on local magnitude (M l) shows a better fit for large magnitudes using a second order equation against to a linear relationship, and the actual quadratic formula based on 61 events is the following: \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $\begin{gathered} M_w = 1.37( \pm 0.28) + 0.39( \pm 0.18)M_l + 0.061( \pm 0.026)M_l^2 \hfill \\ (M_w :1.9 - 5.5;M_l :1.4 - 5.5). \hfill \\ \end{gathered} $ \end{document}.In the intermediate focal depth Vrancea zone of the south-eastern bend of the Carpathians (44.5–46.5N; 25.5–28.0E) the number of body wave magnitudes is the largest one (20) among the local (8), the surface wave (14) and the duration (17) magnitudes. The linear relationship between the moment (M w) and the body wave (M b) magnitudes has the following form: \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $M_w = 1.20( \pm 0.08)M_b - 0.76( \pm 0.40)(M_w :4.1 - 7.7;M_b :3.8 - 7.3).$ \end{document}.The relationships of the different (M l, M s, M b, M d) magnitudes are also presented in the paper.

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The source parameters and dimensions of the three most important earthquakes (Zsolna - Jan. 15, 1858, I o = VIII EMS; Jóko - Jan. 9, 1906, I o = VIII EMS; Jóko- Jan. 16, 1906, I o = VII-VIII EMS) of the area studied are estimated as follows: Event (Magnitude, Rupture area, Max. Displacement); Jan. 15, 1858 Zsolna (5.5 Ms, 22-36 km2, 8-11 cm); Jan. 9, 1906 Jóko (5.7 MS, 40-55 km2, 12-16 cm); Jan. 16, 1906 Jóko (5.3 MS, 12-24 km2,4-8 cm). The average recurrence that we may expect an earthquake of M = 2.3 every 1 year, an earthquake of M = 3.7 every 10 years and an earthquake of M = 5.1 every 100 years in this source zone. The probabilistic seismic hazard assessment predicts 1.2-1.7 m/sec2 peak ground accelerations, and 6.6-7.2 maximum (theoretical) earthquake intensity values with 10% chance of surpassing for an exposure time of 100 years in the area.

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The source parameters and dimensions of the tow strongest earthquakes (July 1, 1829, I o = VII-VIII EMS; October 15, 1834,  I o = IX EMS) in Érmellék area are estimated as follows  Date of the event     Focal depth     Magnitude    Rupture area          Max.                                                                                                       displacement July  01, 1829           21-33 km         5.5-5.7         33-55 km2        11-16 cm October 15, 1834     23-28 km         6.5-6.6        266-358 km2      74-90 cm  The average recurrence that we may expect an earthquake of M ≥ 0.7 every 1 year, an earthquake of M ≥ 2.9 every 10 years and an earthquake of M ≥ 5.0 every 100 years in this source zone. The probabilistic seismic hazard assessment predicts 1.1-1.4 m/cm2 peak ground accelerations, and 6.3-7.4 maximum (theoretical) earthquake intensity values with 10 % chance of exceedance for an exposure time of 100 years in the area.

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In the seismic source zone of Bánát more than 600 earthquakes are known since 1773 among them six events with magnitude of 5.0–5.7 measured on the surface magnitude scale. The macroseismic reinterpretation of the April 2, 1901 earthquake yields epicentral intensity of VII on the European Macroseismic Scale, and a focal depth value of 12 km. Based on empirical relations the maximum rupture area is estimated as 50–55 km 2 and the maximum displacement along the fault is about 16 cm in the Bánát seismic zone due to the M S = 5.7 event occurred on July 12, 1991. The average recurrence that we may expect an earthquake of M ≥ 3.4 every 1 year, an earthquake of M ≥ 4.3 every 10 years and an earthquake of M ≥ 5.3 every 100 years in the studied source zone. The probabilistic seismic hazard assessment predicts 1.3–2.1 m/sec 2 peak ground accelerations, and 6.7–7.3 maximum (theoretical) earthquake intensity values with 10% chance of exceedance for an exposure time of 100 years in the region.

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Based on a complete dataset of the average magnitude M, the recurrence curve predicts an earthquake of magnitude M = 5 every one year, an earthquake of magnitude M = 6  every ten years, and an earthquake of magnitude M = 7 every one hundred years in the Carpathian Basin on average. The curve of elastic energy release of earthquakes does not indicate any noticeable periodicity in the Carpathian Basin based on the observations of nearly 500 years (1500- 1995). The average yearly energy release is 6.1E+13 joule in the whole Basin and the contribution of the Háromszék-Vrancea region to this amount is 4.8E+13 joule/year, while 1.3E+13 joule/year is the product of the remaining large part of the studied area. That is the vast portion of seismic energy is released in an area of only about 6% of the whole Carpathian Basin. According to the results of probabilistic seismic hazard estimations the highest hazard is expected in the region of Háromszék-Vrancea (Romania), where the expected peak horizontal ground accelerations 0.30g, 0.38g and 0.48g respectively will not be exceeded with 75% probability during 50, 100 and 250 years using s=0.5 value in the attenuation.

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The source parameters and dimensions of the three most important earthquakes (Komárom 1763, Io = IX EMS; Komárom 1783, Io = VII-VIII EMS; Mór 1810, Io = VIII EMS) of the area studied are estimated as follows     event                        focal depth   rupture area    max. displacement Jun. 28, 1763 Komárom   7.6 km     93 - 125 km2   29 - 35 cm Apr. 22, 1783 Komárom  11.5 km     18 -  36 km2   6 - 11 cm Jan. 14, 1810 Mór             5.0 km     18 -  45 km2   6 - 14 cm The average recurrence that we may expect an earthquake of M=2.7 every 1 year, an earthquake of M=4.0 every 10 years and an earthquake of M=5.3 every 100 years in this source zone. The probabilistic seismic hazard assessment predicts 1.4-2.0 m/cm2 peak ground accelerations, and 6.9-7.2 maximum (theoretical) earthquake intensity values with 10% chance of exceedance for an exposure time of 100 years in the area.

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In the small seismic source zone of Kecskemét 203 earthquakes are known between 1739 and 2006, and about 90 percent of them have a magnitude value not more than 3.0, however the strongest event on July 8, 1911 has 5.6 surface-wave magnitude. Concerning the latter earthquake the maximum (epicentral) intensity I = VIII (EMS) was observed in the area enclosed by Kecskemét, Katonatelep and Hetényegyháza locations. The quake caused significant damage to buildings (I ≥ VI EMS) on about 6 thousands square kilometres and was felt (I ≥ III EMS) on some 85 thousands square kilometres. The focal depth is estimated as 11 km directly from the individual intensity data points. During the earthquake liquefaction (sand crater) occurred in the epicentral area and some electromagnetic effects were also observed. Studying the source dimensions we conclude the rupture area is between 40 and 67 square kilometres and the maximum displacement along the fault is estimated to 14–20 centimetres for the Kecskemét earthquake of July 8, 1911. A probabilistic seismic hazard assessment predicts 1.1–1.5 m/s 2 peak ground accelerations, and 6.6–7.1 maximum (theoretical) earthquake intensity values with 10% chance of exceedance for an exposure time of 100 years in the studied area.

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The seismicity and seismic hazard of the Carpathian Basin are studied in this paper based on a recent comprehensive database cataloging over 20 thousands earthquakes between 456 and 1995. The epicentre distributions of these events indicate the geographical positions of the most active tectonic processes in the region. Among them the south-eastern bend of the Carpathians (Háromszék-Vrancea zone, Romania) and the area of south-eastern Alps have the highest seismic activity. The former source area is very specific by its strong seismicity from the intermediate depth domain (70-170 km). The intermediate-depth sources are deepening nearly vertically but in somewhat SW direction and the separation of the crustal earthquakes from the events connected to the lithospheric plate subsiding into the astenosphere is well observed at about 50 km, which is the depth of the Mohorovičić discontinuity (MOHO) in this region. The lithospheric plate subsiding to the depth of 150-200 km is supposed to be disconnected around 50 km. Some weakness of this slab can also be assumable based on the lower seismic activity observed between 100-120 km.

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