Historical Seismograms - Evidence from the AD 2000 Izu Islands ...

306 R. Muir Wood, G. Woo, and H. Bungum1927, with Ms = 5.3 (Figure 3). The large Oslofjord earthquake in 1904 (23 October)has, in comparison, an Ms magnitude of 5.4 when calculated based on thesame magnitude-felt area relationship.From the end of the Cretaceous to the present, which is a period of around65 million years, the North Sea region has not followed the fundamental pattern ofrifting and extensional basin tectonics that characterized the crustal deformationover the previous 200 million years. The most significant tectonics has involvedepisodes of regional dome uplift associated with density changes in the underlyingasthenosphere. These have not been symmetrically disposed about the North Seain time; the uplift of Scotland and the Shetland platform took place around 60Ma, while the beginning of the uplift of western Norway can be dated at around30 Ma (Groth and Muir Wood, 1985). The current seismotectonic regime appearsto reflect the continuation of some of the most significant late Tertiary tectonicevents through into the present.REFERENCESAmbraseys, N. N. (1985a). Magnitude assessment of Northwestern European earthquakes,J. Earthq. Eng. Struct. Dyn., 13, 307-320.Ambraseya, N. N. (1985b). The seismicity of western Scandinavia, J. Earthq. Eng. Struct.Dyn., 13, 361-399.Bungum, H., J. Havskov, B. Kr. Hokland, and R. Newmark (1985). Contemporaryseismicity of northwest Europe, Annales Geophysicae, 4B, 567-576.Groth, A. and R. Muir Wood (1985). The Tertiary uplift of western Norway, in preparation.Keilhau, B. M. (1836). Efterretninger om Jordskjaelv i Norge, Mag. for Noturwidenskoperne,12, 83-165.Kolderup, C. F. (1913). Norges Jordskjdv, Bergens Museums Aarbok, 8, 152 pp.Neilson, G. (1979). Historical seismicity of the North Sea, in Energy in the Balance, Brit.Ass. Adv. Science, Edinburgh, 119-137.NGI, NORSAR, and Principia (1984). Seismic Hazard Evaluation for the Sleipner Field,Report prepared for Statoil a.s., Stavanger, Norway, 172 pp.NORSAR, NGI, and Principia (1984). Earthquake Loads for the Troll Field, Reportprepared for Norsk Hydro a.s., Oslo, Norway, 260 pp.NORSAR, NGI, and Principia (1985). Gullfaks C Seismic Hazard Analysis, Report preparedfor Statoil as., Stavanger, Norway, 185 pp.Principia Mechanica Ltd (1982). British Earthquakes, Report prepared for CEGB, SSEBand BNFL, London, U.K.Principia Mechanica Ltd (1985). The Seismicity of the North Sea, Report prepared forthe Department of Energy, London, U.K.Reusch, H. (1887). Jordskjaelvet Natten ti1 25 Oktober 1866, Naturen, 7.Sellevoll, M. A., 3. Almaas, and A. Kijko (1983). A Catalogue of Earthquakes Felt inNorway 1953-1975, Report, Seismological Observatory University of Bergen, Norway.Thommassen, T. C. (1888). Berichte iiber die, wesentlich seit 1834, in Norwegian eingetroffenenErdbeben, Bergens Museums Aarsbertning 1888, 52 pp.Woo, G. and R. Muir Wood (1984). British seismicity and eeismic hazard, Proceedings,Eighth World Conference on Earthquake Engineering, Volume I, 39-44, Prentice-HallInc., New Jersey, U.S.A.