FURTHER TITLES IN THIS SERIES / F. A. VENING MEINESZ THE EARTH'S CRUST AND MANTLE 2 T. RIKITAKE ELECTROMAGNETISM AND THE EARTH'S INTERIOR 3 D. W. COLLINSON, K. M. CREER and S. K. RUNCORN METHODS IN PALEOMAGNETISM 4 M. BÀTH MATHEMATICAL ASPECTS OF SEISMOLOGY 5 F. D. STACEY and S. K. BANERJEE THE PHYSICAL PRINCIPLES OF ROCK MAGNETISM 6 L. CIVETTA, P. GASPARINI, G. LUONGO and A. RAPOLLA PHYSICAL VOLCANOLOGY 7 M. BÂTH SPECTRAL ANALYSIS IN GEOPHYSICS 8 O. KULHANEK INTRODUCTION TO DIGITAL FILTERING IN GEOPHYSICS 9 T. RIKITAKE EATRHQUAKE PREDICTION 10 N. H. RICKER TRANSIENT WAVES IN VISCO-ELASTIC MEDIA 11 W. L. PILANT ELASTIC WAVES IN THE EARTH 12 A. J. BERKHOUT SEISMIC MIGRATION 13 V. C. DRAGOMIR, D. N. GHITAU, M. S. MIHAILESCU and M. G. ROTARU THEORY OF THE EARTH'S SHAPE 14A A. J. BERKHOUT SEISMIC MIGRATION. Imaging of acoustic energy by wave field extrapolation. A. Theoretical Aspects (second, revised and enlarged edition) Developments in Solid Earth Geophysics 15 PROCEEDINGS OF THE SEVENTEENTH ASSEMBLY OF THE EUROPEAN SEISMOLOGICAL COMMISSION Budapest, 24—29 August 1980 EDITED BY E. BISZTRICSANY and GY. SZEIDOVITZ Seismological Observatory of GGRI, Hungarian Academy of Sciences Budapest, Hungary ELSEVIER SCIENTIFIC PUBLISHING COMPANY Amsterdam — Oxford — New York 1983 Joint edition published by Elsevier Scientific Publishing Company, Amsterdam, The Netherlands and Akadémiai Kiado, The Publishing House of the Hungarian Academy of Sciences, Budapest, Hungary The distribution of this book is being handled by the following publishers for the U.S.A. and Canada Elsevier Science Publishing Company, Inc. 52 Vanderbilt Avenue, New York, New York 10017, U.S.A. for the East European Countries, Democratic People's Republic of Korea, Republic of Cuba, Socialist Republic of Vietnam and People's Republic of Mongolia Kultura Hungarian Foreign Trading Co., P.O.Box 149, H-1389 Budapest, Hungary for all remaining areas Elsevier Scientific Publishing Company Molenwerf 1, P. O. Box 211, 1000 AE Amsterdam, The Netherlands ISBN 0-444-99662-1 (Vol. 15) ISBN 0-444-41799-0 (Series) © Akadémiai Kiado, Budapest 1983 Printed in Hungary PREFACE The European Seismological Commission /ESC/ held its 17th General Assembly in Budapest between 21 and 2 3 August, 1980,at the invitation of the Hungarian Academy of Sciences and the Hungarian Geophysical Society. At the same venue, the European Geophysical Society /EGS/ held its Seventh Annual Meeting from 24 to 29 August, at the invitation of the Lorand Eötvös Uni- versity and the Hungarian Geophysical Society. The present Volume contains papers presented on the ESC Assembly, respectively on the ESC-EGS Joint Meetings. General- ly, the manuscripts are reproduced in their original form. Editorial interventions were restricted to improving some figures and removing misprints and errors of spelling but those of division were not corrected. Consequently the authors are fully responsible for their contributions in all respects. The editors would like to thank all authors for contribut- ing to the success of this Volume. Thanks are also due to the Publishing House of the Hungarian Academy of Sciences for pleasant collaboration, consideration in several matters and a job well done. XIII PRESIDENTIAL ADDRESS A. REINIER RITSEMA 1. The European Seismological Commission was created during the IUGG General Assembly in Brussels on the 28th of August 1951. Personally, it was also my first international geophysical conference. Sixteen General Assemblies of ESC have followed, most of them highly successful and attended by many European seismologists. The increasing interest in these meetings is shown in the larger numbers of participants /more than 150 from 25 countries in the present case/, and of contributing papers /a total number of 152 scientific papers was present- ed in the Budapest meetings/. Specially gratifying is the steadily rising attendance from countries outside the European region, indicating the improtance that is attribut- ed to the ESC meetings. The internal rules and statutes of ESC say that it is the task of its members to promote work in seismology in the European area, defined as the region between 30-90°N and 30°W - 40/60°E. As positive developments during the 29 years of ESC we may point to the impressive increase of active seismologists in the region, to the even more spec- tacular extension of the seismic network of the region, and to the multitude of scientific publications of which many were produced for and presented in meetings of the ESC. Im- portant progress was made in the study of seismicity of the European area, of instrumentation and data acquisition, of the physics of the earthquake source, of the structure of the crust and upper mantle of the region, of microseisms and seismic noise, and of more theoretical problems, such as wave propagation and earthquake generating stress fields. 2. For the record, some salient points of the past two years since the 16th General Assembly in Strasbourg have to be layed down and remembered: 2.1 With regret we have to mention the decease of a number of colleagues and friends, among them three former presidents and one titular member. They are: XV Prof.P.Caloi /-1978/: after his presidency ended in Utrecht, 1958, he did not attend another ESC meeting; as a European seismologist, however, he was extremely productive till the last; Prof.E.F.Savarensky /18 July 1911 - 27 January 1980/: for many years the nestor of USSR seismologists and for more than 20 years active in ESC; many of us did meet him apparently in good health a month earlier in the IUGG meetings of Canberra; Prof.W. Hiller /2 February 1899 - 31 July 1980/: first president of ESC and initiator of the European coopera- tion in the Commission; he reached the age of 81; Mme. Dr. M.Grigorova /1980/: for many years the ESC ti- tular member for Bulgaria and the driving force behind the expansion of seismology in her country; Dr.M.A.Choudhury / - 17 December 1979/: born and educat- ed in Pakistan, he worked in the IPG's of Paris and Strasbourg on earthquake mechanisms, wave propagation a.o.; he reached the age of only 53; Dr.I.Miyashkin /1980/: not a regular participant at ESC meetings; active in the USSR programs on earthquake prediction. These European seismologists, our colleagues and friends, will be missed by many of us. Their names will stay on file with ESC. 2.2 In the past two years period at least 12 earthquakes occurred in the European area causing important damage to human structures. It all started with the Tailfingen earthquake of September 3, 1978 causing damage in Southern Germany and felt by many participants of the Strasbourg General Assembly. In total, there were nearly 200 casualties in the past two years and several thousands of injured in our re- gion, most of them in the M7 Montenegro-Albanian earth- quake of April 15, 1979 and in the M6.9 Azores earth- quake of January 1, 1980. On the invitation of our Albanian colleagues some ESC officers visited the country a year after the main shock to witness the re- markable recovery of destroyed villages in the North. Other presidential terms may have been more disastrous with respect to earthquakes, but also now after 29 years of ESC, none of the many European earthquakes in this period were forecasted. 2.3 European seismologists have been very active during this period. The reports of the subcommissions will be presented elsewhere and therefore will not be re- peated here. The list of symposia, workshops, study groups and seminars taking place during the period and having some relationship with the case of general and XVI European seismology, comprises the formidable number of 25, with an accumulated duration of 140 days! This extreme expansion of opportunities to meet colleagues working in the same field asks for some co-ordination in future years. 2.4 Another matter of some concern is the fact that most of these meetings were not /co-/sponsored by ESC. Agencies apparently interested in problems related to seismology in general and in the European area in particular are IASPEI, ICG, IAEE, EAEE, EGS local and regional seismo- logist groups, UNESCO, UNDP, UNDRO, CSCE, KAPG, Council of Europe, CCMS, UNCD, ESA, ICTP, a.o. In principle, ESC stimulates initiatives of individuals as well as of interested organizations. It is hoped, however, that in future, also through actions of the ESC subcommis- sions the needed co-ordination between outside activ- ities and ESC will be strengthened and expanded. 3. For the next two years period ESC should pay special atten- tion to the problems in the applied side of seismology, and notably in terms of research in the field of earthquake pre- diction. 3.1 In the past five years the demands for expert state- ments on earthquake hazard, risk and prediction have grown abundantly. ESC reacted in some modest way by the organization of special symposia specially devoted to the problems, such as that on earthquake risk for nuclear power plants in Luxemburg /fall 1975/, and that on the analysis of seismicity and seismic risk in Liblice /fall 1977/. In the meantime many ESC members are working hard on the problem of the assessment of seismic risk and the preservation of life and human structures in the case of an earthquake. But the stage of the actual fieldwork in Europe in this branch of seismology is still very preliminary. 3.2 In the fall of 1979 ESC started a rapid survey of earth- quake prediction programs known to our titular members. It revealed that nearly all European countries are en- gaged in work that somehow is related to earthquake prediction. Specific topics range from the compilation of catalogues, the study of earthquake statistics, seis- mic sequences, geological and geodetic aspects, earth- quake mechanisms, instrumentation and laboratory experi- ments to historical case studies. At some specific time each of these subjects can contribute significantly to the prediction of earthquakes, but on its own they are insufficient to be classified as such. Integrated programs of multidisciplinary kind are known of: Portugal, Spain, Italy, Yugoslavia, Albania, Greece, Turkey, Bulgaria, Rumania, the USSR and Iceland /see also Proceedings 2nd Workshop on European Earthquake Prediction Programme. ESA publication SP-156, 1980/. 2 XVII Some of these programs are actively supported by other nations, such as the UK, France, the FRG, Switzerland, the USSR and the USA. Some of the programs have al- ready started, but the majority still is in the pre- paratory stage. This means that, in comparison with some other countries outside Europe, we are not yet in the frontline. 3.3 Yet, what the variety of earthquake types concerns, Europe is in a favourable position for significant con- tributions in the field. The European area comprises not only seismic zones of the transcurrent fault type /North Anatolian zone/, but also the subduction type /Hellenic- and Calabrian Arcs/, of the tensional type /Iceland and Mid-Atlantic ridge/, and of the very low seismicity type /non-Alpide part of Europe/. It seems clear that co-ordination of the different act- ivities and programs is a necessity. And it is here that a real task lies for the ESC. 3.4 It is with satisfaction/therefore, that as a first step two new subcommissions have been installed during the 17th General Assembly of ESC in Budapest, one on earth- quake prediction research, and the other on engineering seismology. We do not expect immediate positive results in the form of predictions in time, place and magnitude, but we have confidence that ESC, through this inter- mediancy, will contribute more directly to the factual problems of a great part of the European population living in earthquake-prone regions. Moreover, the steering and co-ordination function of ESC with outside parties could find a solid base here. 4. In 1964 the 10th General Assembly of ESC was held in Buda- pest. In the 29 years of ESC existence it is the only case that a town for the second time takes the responsibility to act as host for ESC. This is a compliment to the country of Hungary. We thank the Hungarian Academy of Sciences for their generous hospitality, the members of the local organiz- ing committee under the chairmanship of Prof.L.Stegena for their arrangements and efficient help to participants, and the editorial committee under the chairmanship of Prof. E. Bisztricsâny for their care for the scientific proceedings. We are grateful for all work done by these and the numerous uncalled officials and non-officials that made the 17th General Assembly of ESC a great success. The present Volume is a token for their efforts. XVIII PMC. oi tkdUtk A&AZjnbly ofi tiin ESC Budapest, 19 SO THE BULGARIAN NATIONAL TELEMETRIC SYSTEM FOR SEISMIC DATA INTERPRETATION. L.CHRISTOSCOV, D.SAMARDJIEV, P.DANEV, TZ.GEORGIEV AND L.PETROV Geophysical Institute, Bulgarian Academy of Sciences, Sofia, Bulgaria The recent years were characterized by the activation of the seismic processes in the Balkan region* The strong earthquakes which occurred in Vrancea, Velingrad, Thessaloniki and Montenegro have shown that the available seismic station network was not sufficiently effective. The quick operation in the damaged regions required rapid and correct information on major earthquake parameters. Since 1978 the Bulgarian authorities started to establish a principally new national telemetric system for seismic data interpretation to solve the following main problems: a/ Exact registration of all the shocks on the territory of Bulgaria and surrounding areas within the magnitude range 3-6,5 and rapid interpretation of the data. b/ Using these data for deeper investigations of the seismic situation in the country. The Bulgarian telemetric system at present includes 7 peripheral stations /see Fig. 1/: Dimitrovgrad DIM Kurdzhali KDZ Musomishta MSM Preselentzi PSN Pavlikeni PVL Sofia SOF Vitosha VTS These stations are located in the. most active seismic zones of the country. The system will be extended to 16 stations for which technical opportunities exist. Each station runs like an.autonomous one /on-site record/ and in the same time like a peripheral station of the seismic system. All the seismological and telemetric equipment were produced by Teledyne Geotech. Each peripheral station includes the following main units: - seismometer type S-13, short period /natural period 1 s/, vertical mode operation; - twc stages preamplifier with low gain output LG /magnification up to 1000 times - 60 dB/ and high gain output HG /magnification up to 1000000 times - 120 dB/. Both gains are selectable in 6 dB steps depending on the seismic noise. The magnifications used are shown in Fig. 2. 3 BULGARIAN TELEMETRIC SEISMIC NETWORK August 1980 N ^ ^ " ^ " ^ ^ ^ ^^ y %!>^^^^ 1 ) Jk?^^^ J 1 : / ^ \ \\ S Μ Ί 1 \Γ^' ^ 0> 1 ? ^MSM KDN Ç \ Fig. 1 STANDARD FREQUENCY RESPONSE DIAGRAM MAGNIFICATION V if tao Hi FREQUENCY MAGNIFICATION FOR EACH STATON SOF V x 008 VTS V x 16 MSM V x 16 PVL V x 1 PSN V x 4 DIM v x ; KDZ V x 1 Fig. 2 4.