The Paks M icroseismic M onitoring Network has been operating since April 1995.
Although the given geological and background noise conditions are far from ideal at some stations, with average noise conditions the typical detection threshold of the network (supported by other existing stations) is around 1.5-2.0 ML, som ewhat lower in the middle o f the country and a little higher towards the border regions. This means that for the first time in the history of Hungarian earthquake seismology, in m ost part of the country, it is very unlikely that felt earthquakes go undetected.
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During nearly two years o f operation about thirty local earthquakes were detected and located within the Hungarian national boundary. Some others occurred in neighboring countries and were sometimes sufficiently large and near to be felt in Hungary and thus merit consideration in seismic hazard studies.
The magnitude o f the detected Hungarian earthquakes range from 1.6 to 3.7 ML, typical of intraplate seismicity. Geographically the epicenters also show a near random distribution expected in an intraplate area with no dominant tectonically active features.
Comparing historical seismicity with the recent events, it shows that the recent earthquakes, in general, lie near to clusters of historical activity. Three events at Szabadszallas are exceptions in the sense that they appear not to be associated with historical activity but lie near a cluster of historical events some 30 km to the east.
REFERENCES
Bakun, W.H. and W.B. Joyner (1984). The ML scale in central California. - Bull. Seism. Soc.A m . 7 4 ,1 8 2 7 -1 8 4 3 Bonder, I., (1994). H ypocentre determ ination o f local earthquakes using genetic algorithm . Acta Geod. Geoph.
Hung., 2 9 ,1 - 2 ,3 9 - 5 6
Evernden, J. (1970). Study o f regional seism icity and associated problem s. - Bull. Seism. Soc. Am. 60, 3 93-446 Lee, W .H.K. and J.C. L ahr (1975). H Y P071 (Revised): A com puter program f o r determ ining hypocenter, magnitude, a n d fir s t m otion pattern o f local earthquakes, U. S. G eological Survey O pen-file report pp.
75-311
M onus, P. (1995). Travel -tim e curves a n d crustal velocity m o d elfo r the Pannonian basin, M TA G G K 1Technical report.
Mdnus P. and Gy. Szeidovitz (1991). Talajnyugtalansdg meresek a Paksi Atom erom u kiirnyezeteben (M easure
m ents o f noise background in the vicinity o f the Paks NPP, in H ungarian), M TA GGKI Szeizm ol6giai osztdly in ak jelentese.
Rethly, A. 1952. A kdrpdtm edencekfoldrengesei (4 5 5 -1 9 1 8)(Earthquakes in the Carpathian Basin, in Hungarian), A kadem iai Kiado, Budapest, 510 p.
Scholz, C. H. 1968. The frequency-m agnitude relation o f m icrofracturing and its relation to earthquakes. - Bull.
Seism. Soc. Am. 58, 399-416
T<5th L. 1981. E stim ation o f Seism ic Detection T hresholds o f Seism ograph Stations in Hungary, A cta Geodaet., Geophys. et M ontanist. Hung. 16,469-475
Toth, L„ P. M 6nus and T. Zsi'ros (1996). Hungarian Earthquake Bulletin, 1995. -G e o R is k , Budapest.
Toth, L., P. M onus and T. Zsi'ros (1997). Hungarian Earthquake Bulletin, 1996. - GeoRisk, Budapest.
Zsi'ros, T., P. M onus and L. T 6th (1988). Hungarian earthquake catalog (456-1986). - G eod. and Geophys. Res.
Inst. Budapest, 182 p.
Technical Reports
A Paksi A tom erom u m ikroszeizm ikus m egfigyelo hdlozata: Tervezet, G eoR isk, January 1994.
(M icroseism ic M onitoring N etw ork o f the Paks NPP: A D raft Plan)
A Paksi Atomerfimu m ikroszeizm ikus m egfigyelo halozata: Potencialis allom ashelyek felkutatasa helyszfni bejdrds alapjan, GeoRisk, April 1994.
(M icroseism ic M onitoring Netw ork o f the Paks NPP: Selection o f Potential Sites w ith Field Studies)
A Paksi A tom erom u m ikroszeizm ikus m egfigyelo halozata: Szeizm ikus hStt6rzaj m6resek a p o te n c ie s allom as- helyeken, GeoRisk, M ay 1994.
(M icroseism ic M onitoring N etw ork o f the Paks NPP: M easurem ents o f B ackground N oise Level at the Potential Sites)
A Paksi Atom erom u m ikroszeizm ikus m egfigyelo hdldzata: Szakertoi konzflium az allom ashelyek veglegesite- s6re, G eoR isk, June 1994.
(M icroseism ic M onitoring N etw ork o f the Paks NPP: C onsultation o f E xperts for Finalizing Sites o f the Seism ological Stations)
A Paksi Atom erom u m ikroszeizm ikus megfigyelo hdldzata: T ervdokum entaciok 6s a mdroallomasok kivitelezc- se, G eoR isk, N ovem ber 1994.
(M icroseism ic M onitoring Netw ork o f the Paks NPP: D ocum entation o f D rafts and Preparation o f Seism ological Stations)
A Paksi A tom erom u m ikroszeizm ikus m egfigyelo hal6zata: Robbantassal tort^no kalibraci6, erz6kenysegi kiiszob, sebess<5gmodell, GeoRisk, Septem ber 1995.
(M icroseism ic M onitoring N etw ork o f the Paks NPP: C alibration by Blasts, D etection Threshold, Velocity Model)
A Paksi Atom erom u m ikroszeizm ikus m egfigyelo halozata: Feldves Jelentes, 1995 I., GeoRisk, July 1995.
(M icroseism ic M onitoring Netw ork o f the Paks NPP: Sem iannual Report for the first h alf o f 1995)
A Paksi Atom erom u m ikroszeizm ikus m egfigyelo halozata: Feleves Jelentes, 1995 II., GeoRisk, January 1996.
(M icroseism ic M onitoring N etw ork o f the Paks NPP: Sem iannual Report for the second half o f 1995) A Paksi A tom erom u m ikroszeizm ikus megfigyelo' hdl6z.ata: Feleves Jelentes, 1 9 9 6 1., GeoR isk, July 1996.
(M icroseism ic M onitoring Netw ork o f the Paks NPP: Sem iannual Report for the first h alf o f 1996)
A Paksi Atom erom u m ikroszeizm ikus m egfigyelo'hdlozata: F<M6ves Jelentes, 1 9 9 6 II.. G eoR isk, January 1997.
(M icroseism ic M onitoring Netw ork o f the Paks NPP: Sem iannual Report for the second half o f 1996)
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Fig. 1. G eographical distribution o f seism ic stations o f the M icroseism ic M onitoring N etw ork (black circles) and other supporting stations (grey circles) in H ungary
Frekvencia [Hz)
Fig. 2. Typical noise spectra recorded at a loose sedim ent and at an outcrop site, respectively
Fig. 3. Netw ork detection capability with average noise conditions day (up) and night (down).
C ontour values are given in R ichter local m agnitudes (M L).
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Dunaharaszti - 1996/10/21 01:23 Fig. 4. Seism ogram s o f the Duna
haraszti earthquake on 21st O cto
b er 1996, 1:23:26 UTC (M L=2.5) show n by the M icroseism ic M oni
toring Netw ork. T he vertical axis is ground velocity in m/s.
Fig. 5. Earthquakes in Hungary, 1995-96
Seism ic safety o f the P aks N uclear Pow er Plant pp. 123-152.
Neotectonic investigations by high resolution seismic profiling
TO TH , Tam as and H O RV A TH , Ferenc
D epartm ent o f G eophysics Eotvos Lorand University H -1083, Budapest, Ludovika ler 2
1. Introduction
Several studies have dealt with the geology in the vicinity o f the Paks N uclear Pow er Plant. Special attention was paid to the age and correlation o f faults cutting through M iocene and Pannonian strata. M ost Hungarian and foreign geologists and geophysicists agree that som e basem ent faults have been reactivated in the area during the late N eogene. H owever, debates are still going on if fault activity continued during Q uaternary, and therefore recent activity and capability o f faults can not be considered a closed subject. H igh resolution shallow -seism ic m easurem ents can contribute vital inform ation for the clarification o f the problem . The aim o f this report is to present the results o f the river Danube high resolution seism ic survey carried out by the G eophysical D epartm ent o f the Eotvos U niversity (ELTE) and review the reprocessing o f onland shallow -seism ic lines m easured by the E otvos Lorand G eophysical Institute (ELGI). Joint interpretation o f al! o f these seism ic lines has been carried out and the results are presented.
The G eophysical D epartm ent carried out a seism ic survey on the river Danube in O ctober 1994 with the participation o f foreign experts. This paper includes five multichannel seism ic lines m easured w ith a watergun source. T hese five profiles have been m easured in the 15 km vicinity o f Paks N uclear Pow er Plant and provide information about the strata underneath the river from the riverbottom down to a depth o f m ore than 500 m eters.
The aim o f the survey w as to obtain a detailed image o f the faults crossing the D anube in ord er to carry out neotectonic and stratigraphicevaluation. The total length o f the five profiles presented (D anube-202, Danube-203, Danube-205, D anube-207 and Danube-208) is 16.1 km. In addition to these profiles further multi-channel lines from the D anube survey (Danube-201, D anube-206 and D anube-209) and reprocessed versions o f onland shallow -seism ic lines Pa-2a, Pa-2b, Pa-3b, Pa-12, Pa-13, Pa-14, Pa-15 and P a -17 w ere used for interpretation.
C hapter 2. is a b rief sum m ary of seism ic profiling introducing both surveying and processing techniques to those who are not specialists in this field. A im o f this chapter is to provide the necessary background inform ation for later chapters. In this short introduction we could not discuss all the details o f the seism ic surveying and the interested reader is referred to M cQ uillin et al. 1984 and Yilm az 1987.
C hapter 3 discusses the field param eters and processing sequence o f the multichannel D anube profiles, w hile C hapter 4. is a short description o f the onland shallow -seism ic sections.
In C hapter 5 the com plex interpretation o f the shallow -seism ic profiles is discussed and a possible correlation o f the observed faults is presented. Special attention has been paid to differentiate faulted structures from disturbances caused by shallow layer inhom ogeneities. C onclusions are draw n in the final chapter (6).