Neotectonics in Norway NGU Report 99.007 Neotectonics in Norway Annual Technical Report 1998 NTNU Trondheim Geological Survey of Norway P.O.Box 3006 - Lade N-7002 Trondheim, Norway REPORT l 4 3904011 Report no.: 99.007 ISSN 0800-3416 Grading: Confidential until 1/7-2001 Title: Neotectonics in Norway, Annual Technical Report 1998 Editors: Client: John Dehls and Odleiv Olesen Amoco, Norsk Hydro, Phillips Petroleum, Statkraft, NFR, NGU, NORSAR, NPD and SK Contributors: Contributing institutes: L.H. Blikra, L. Bockmann, H. Bungum, J. Dehls, NGU, NORSAR, NPD, SK, SINTEF, Rogaland S. Fanavoll, P. Goldsmith, E. Hicks, B. Hilmo, T. Research, Phillips Petroleum, NTNU, UiO Klemetsrud, Æ. Jóhannsson, C. Lindholm, E. Mauring,O.Olesen,L.Olsen,F.Riis,L.Rise,D. Roberts, J.S. Rønning, A. Sylvester Deposit name and grid-reference: Number of pages: 206 Price (NOK): Map enclosures: 7 Fieldwork carried out: Date of report: Project no.: Person responsible: 1998 12/03-1998 2757.00 Summary: The NEONOR project represents a national effort by several national research and mapping institutions to study neotectonic phenomena through a multidisciplinary approach. Information on present land uplift, seismicity, rock stress and postglacial faults is compiled in a 1: 3 million map of Norway and adjacent areas. There is good evidence for a conjugate set of normal faults perpendicular to the extensive system of NE-SW trending reverse faults in north- ern Fennoscandia. The Nordmannvikdalen fault in northern Troms and the Stuoragurra Fault in western Finnmark constitute the Norwegian part of this fault province. Nine other faults occur in northern Finland and northern Swe- den. Trenching of the Stuoragurra Fault in Masi has revealed that the seven metre high scarp was formed in one seismic event (magnitude 7.4-7.7) during the very last part of the last deglaciation in Finnmark (i.e. c. 9,300 years BP) or shortly afterwards. Large-scale rock avalanches and gravitational faulting in northern Troms are most likely triggered by one or more earthquakes (magnitude larger than 6) immediately after the last deglaciation. New seismic mini-arrays in the Ranafjord and Bremangerlandet areas have revealed areas of increased seismicity. Several hundred earthquakes have been detected in the outer Ranafjord area during the last one and a half years, with magnitudes up to 2.8. This is very high for onshore Baltic shield areas. Neotectonic activity in the Rana, Masi and Kåfjord areas seems to influence the ground water flow. Several distortions in the Quaternary reflectors have been mapped in the northern North Sea area. Some of the subtle features may represent tectonic faults resembling the postglacial faulting previously reported by Hovland (1983). No conclusive evidence for a tectonic cause of the structures can, however, be drawn from the interpretation of the 3D seismic data. There is increasing evidence for a major seismic pulse in Fennoscandia and Scotland accompanying each of the deglaciations following the multiple glaciation cycles during the last 600.000 years. It is possible that the interaction of the contraction and dilation of fissures associated with the seismic cycles may assist in concentrating hydrocarbons from their source rocks and pumping them to potential res- ervoir formations. Keywords: Geofysikk Geologi Seismologi Neotektonikk Geologisk risiko Forkastning Skred Landhevning Fagrapport CONTENTS 1 Introduction........................................................................................................................... 1 2 Classification and Quality Assessment of Reported Neotectonic Phenomena (Task 1) ...... 3 2.1 Introduction ............................................................................................................. 3 2.2 Reported neotectonic activity in Norway ................................................................ 4 2.3 Conclusions ............................................................................................................. 6 2.4 References ............................................................................................................. 19 3 Offshore Faulting (Task 2) ................................................................................................. 24 3.1 Interpretation Of Swath Bathymetry And Seismic Data From The Øygarden Fault Zone ............................................................................................................................... 24 3.1.1 Introduction....................................................................................................... 24 3.1.2 Database............................................................................................................ 25 3.1.3 Quaternary geology and bathymetry in the study area...................................... 32 3.1.4 Interpretation focusing on Quaternary reactivation of the fault zone ............... 35 3.1.5 Conclusion........................................................................................................ 37 3.1.6 References......................................................................................................... 37 3.2 Interpretation Of Seismic Data From Hjeltefjorden.............................................. 39 3.2.1 Introduction....................................................................................................... 39 3.2.2 Database............................................................................................................ 40 3.2.3 Quaternary geology and bathmetry................................................................... 42 3.2.4 Interpretation: Neotectonic faulting or current controlled deposition ? ........... 42 3.2.5 Summary and conclusion.................................................................................. 46 3.2.6 References......................................................................................................... 46 3.3 Interpretation of 3D seismic surveys in the northern North Sea and Nordland II and VI areas ........................................................................................................................ 48 3.3.1 Introduction....................................................................................................... 48 3.3.2 Seismic data...................................................................................................... 52 3.3.3 Northern North Sea........................................................................................... 56 3.3.4 Nordland II and VI areas................................................................................... 73 3.3.5 Conclusions ...................................................................................................... 84 3.3.6 References......................................................................................................... 85 4 1:3 000 000 Neotectonic Map and Database (Task 3)........................................................ 87 5 Geology & Geophysics (Tasks 4 & 9)................................................................................ 88 5.1 Rock avalanches, gravitational faulting and its potential palaeoseismic cause..... 88 5.1.1 Rock avalanches and gravitational faulting in Troms county........................... 88 i 5.1.2 Rock avalanches and gravitational faulting in Møre & Romsdal..................... 90 5.1.3 Palaeoseismic cause?........................................................................................ 91 5.1.4 Further research activities................................................................................. 92 5.1.5 References......................................................................................................... 92 5.2 Late Quaternary Faulting And Paleoseismicity In Finnmark, Northern Norway. 93 5.2.1 Summary........................................................................................................... 96 5.2.2 References....................................................................................................... 101 5.3 Reverse-slip offsets and axial fractures in road-cut boreholes from Finnmark: neotectonic stress orientation indicators........................................................................... 103 5.3.1 Introduction..................................................................................................... 103 5.3.2 Regional geology ............................................................................................ 103 5.3.3 The studied areas ............................................................................................ 104 5.3.4 The Laksefjord area ........................................................................................ 104 5.3.5 The western Porsangerfjord area .................................................................... 109 5.3.6 Concluding remarks........................................................................................ 110 5.3.7 An addendum from Trøndelag........................................................................ 112 5.3.8 References....................................................................................................... 113 5.4 Ground-Penetrating Radar Profiles Across Postglacial Faults At Kåfjord (Troms), Masi (Finnmark) And Sodankylä, Finland ....................................................................... 115 5.4.1 Introduction....................................................................................................