The Workshop on the Seismicity and Seismic Risk in the Off­ shore North Sea Area was intended to bring together experts from a variety of disciplines as well as interest groups with involve­ ment in siting, design and construction of offshore structures in the region. Participants came from the fields of geology, seismology, oceanography, geotechnical and structural engineering and risk analysis. The wide range of participant affiliations included institutes, Observatories, universities, oil companies, consultants and insurance firms. All nationalities around the North Sea were present, in addition to some experts from outside the region. All participants were present on the basis of personal invitation. The idea of organizing the Workshop stemmed from conside- tions, such as: the rapidly increasing material and personel investments and versatility of type of structures in the basin.during the past decade; - the present-day important role Jf the North Sea oil and gas production in the economy of Western Europe; and - the increase of potential environmental risks in the region. Although devastating earthquakes are almost unknown in the area and seismic hazard is not great, the seismic risk grows with the growing size and number of structures in the area. The study of the potential seismic risks, therefore, cannot be neglected any more. The siting and design of offshore platforms and submarine pipelines are controlled by the degree of their vulnerability as well as the seismic hazard. in the region.

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Section 1: Geology and Tectonics.- Tectonics of the North Sea Basin and their possible relation to historical earthquakes.- North Sea seismotectonics and the role of geology in offshore seismic risk assessment.- Constraints on seismo-tectonic models for the North Sea.- What happens to the Rhine Graben "sub-plate boundary" where it meets the S. North Sea?.- Geology and tectonics. Panel Discussion. Introductory remarks.- Note: Possible neotectonic fault movements in Norway.- Discussion.- Section 2: Seismicity.- Seismicity of the North Sea Area.- Some problems concerning the seismicity of the North Sea area.- Non-random distribution of earthquakes in the North Sea basin area.- Seismicity and neotectonic structural activity of the Rhine Graben system in Central Europe.- Removal of Ghosts.- (presented by Hoang Trong Pho)/ Commentaires sur une carte seismique de la Mer du Nord et de la Mer de Norvège.- Discussion.- Section 3: Tides, Ocean Waves and Sea Level Changes.- Tidal research and seismicity.- Changes of relative mean sea-level and of mean tidal amplitude along the Dutch coast.- Extreme values of wind speed and wave height in the North Sea for defining design criteria of offshore installations.- Note: Seaquakes, an hazard to offshore platforms?.- Discussion.- Section 4: Instrumentation.- Instrumentation for North Sea seismic data acquisition.- Strong motion earthquake data acquisition and processing.- Ocean bottom seismic instrumentation.- Testing methods related to soil- and structure behaviour under dynamic loading.- Note on the detection and location capability of the Netherlands seismic stations for earthquakes in the North Sea basin.- Discussion.- Section 5: Soilmechanics, Liquefaction, Geotechnology.- Some remarks on the contribution of geo-technical engineering to an estimation of seismic risk.- Problems in soil mechanics and earthquake engineering in the North Sea.- Seismic data requirements for the design of fixed platforms in the offshore North Sea area.- Evaluation of stability of North Sea sites.- Seismology: a geotechnical engineer's view point.- Testing for liquefaction potential.- Modeling of strong ground motion from earthquakes.- Discussion.- Section 6: Risk Analysis.- Evaluation of seismic risk.- Seismic risk and the North Sea.- On some problems concerning seismic risk assessment for offshore structures in the North Sea.- Uncertainty in U.K. seismic hazard analysis 377.- Methodological aspects encountered in the Lower Rhine area seismic hazard analysis.- Outline of procedure for total seismic risk estimation.