[PDF][PDF] Neotectonics, seismicity and contemporary stress field in Norway–mechanisms and implications

O Olesen, H Bungum, J Dehls, C Lindholm… - Quaternary Geology of …, 2013 - ngu.no
O Olesen, H Bungum, J Dehls, C Lindholm, C Pascal, D Roberts
Quaternary Geology of Norway, Geological Survey of Norway Special Publication, 2013ngu.no
Over the last thirty years, through studies of neotectonic phenomena, it has become evident
that the present-day Baltic Shield is not the uniformly quiet, stable, continental-crustal area
that was earlier commonly assumed. In Norway, and northern Fennoscandia as a whole,
detailed seismotectonic investigations, recordings of Late Quaternary faults, stress
measurements and observations of stress-release features have all indicated that
neotectonic movements have been, and still are, quite significant (Kujansuu 1964 …
Over the last thirty years, through studies of neotectonic phenomena, it has become evident that the present-day Baltic Shield is not the uniformly quiet, stable, continental-crustal area that was earlier commonly assumed. In Norway, and northern Fennoscandia as a whole, detailed seismotectonic investigations, recordings of Late Quaternary faults, stress measurements and observations of stress-release features have all indicated that neotectonic movements have been, and still are, quite significant (Kujansuu 1964, Lagerbäck 1979, 1990, Olesen 1988, Bungum 1989, Slunga 1989, Talbot and Slunga 1989, Roberts 1991, 2000, Olesen et al. 1992a, 1995, 2004, Myrvang 1993, Bungum and Lindholm 1997, Muir Wood 1989a, 2000, Stewart et al. 2000, Roberts and Myrvang 2004, Pascal et al. 2005a, b, 2006). Monitoring of seismicity in the adjacent continental shelf, together with data from borehole breakouts, has also greatly increased our knowledge of the contemporary, regional stress regime (Bungum et al. 1991, Gölke and Brudy 1996, Hicks et al. 2000a, Byrkjeland et al. 2000), a factor of no mean importance for the offshore petroleum industry. Neotectonics, and the potential hazards associated with such crustal motions, thus constitute an important component of the Quaternary geology of Norway. Our approach to neotectonic studies follows the definition of neotectonics as given by the International Association for Quaternary Research (INQUA);“Any earth movement or deformations of the geodetic reference level, their mechanisms, their geological origin (however old they may be), their implications for various practical purposes and their future extrapolations”(INQUA 1982). In Norway, the first known report of neotectonic activity is that of Morsing (1757), and over the last 250 years the number of such reports has increased steadily and has now reached more than 80 (Olesen et al. 2004). Additional reports deal with three shallow earthquake swarms along the coast of Nordland (Bungum and Husebye 1979, Bungum et al. 1979, Atakan et al. 1994, Hicks et al. 2000b) and four separate swarms on Svalbard (Bungum et al. 1982, Mitchell et al. 1990, Pirli et al. 2010) that could, dependent on definition, be added to the list (Figure 1). Almost 80% of the reports were published after 1980. Twenty of the claims are situated in the offshore area and more than 60 are located on mainland Norway. A first coordinated attempt to assess the status and many facets of neotectonic activity in Norway came with the ‘Neotectonics in Norway’(NEONOR) project during the years 1997–2000. This aimed at investigating neotectonic phenomena through an integrated approach including structural bedrock mapping, monitoring of microseismicity, recording of stress-release features, study of aerial photographs, trenching, drilling, 14C dating, geodetic levelling and groundpenetrating radar profiling (Dehls et al. 2000a, Fjeldskaar et al. 2000, Hicks et al. 2000a, b, Roberts 2000, Olesen et al. 2004, Rise et al. 2004). Seismic surveying (including available 3D data) and multibeam echo-sounding techniques were used to examine possible offshore postglacial faulting. The shallow parts of eight seismic 3D cubes (located in seismically active areas) were studied to try to locate potential Quaternary deformation features. Results from rock-avalanche hazard projects in Troms and western Norway (Geological Survey of Norway [NGU]) and the ‘Seabed Project’(NORSAR/NGI/UiO/SINTEF) were also included in this major assessment of neotectonic activity on the Norwegian mainland and continental shelf. In this paper we summarise our current knowledge and understanding of neotectonics in …
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