The April 14, 2004 Jan Mayen earthquake

1. The April 14, 2004 Jan Mayen earthquake Mathilde Bøttger Sørensen1, Lars Ottemöller2, Jens Havskov1, Kuvvet Atakan1, Bjarte Hellevang1, Rolf Birger Pedersen1 1Department of Earth Science, University of Bergen, Norway 2British Geological Survey, Edinburgh, UK.

2. Outline • Tectonics • Main shock • Aftershocks • Correlation with tectonics • Conclusions

3. North Atlantic

4. Fault plane solutionsin Jan Mayen region Harvard CMT solutions 1976 - present

5. Detailed bathymetry

6. Norwegian National Seismic Network

7. Main shock

8. Main shock location Magnitude (PDE) Mb = 5.8 Ms = 5.6 Mw = 6.0

9. Main shock location

10. Aftershock study • Aftershock statistics • First 12 hours after main shock for outline of fault plane • Later aftershocks to see if a migration has occurred

11. Aftershock statistics 166 events with M2.5 during first two months after main shock

12. Aftershock location • Two techniques: • Manual location • - M  2.7 • - Uncertainty 10 ms on P, 60 ms on S • - Systematic residuals  laterally varying model • Correlation technique • - Reduces uncertainty to 5 ms • - M  2.2

13. First 12 hoursmanual location

14. Aftershock location • Two techniques: • Manual location • - M  2.7 • - Uncertainty 10 ms on P, 60 ms on S • - Systematic residuals  laterally varying model • Correlation technique • - Reduces uncertainty to 5 ms • - M  2.2

15. First 12 hours manual and correlation

16. Later aftershocks M 2.7 Within 2 months after main shock

17. Later aftershocks

18. Correlation totectonics

19. Earlier activity • Mb = 5.7 earthquake on December 13, 1988 • Relative arrival times within 0.01 s • Aftershocks locations similar

20. Summary and conclusions • Positive corellation between main shock, early aftershocks and the eastern segment of the Koksneset fault, which extends along the JMFZ in the NW-SE orientation • This is the first example in the Northern North Atlantic, where such a direct correlation is documented • Later aftershocks: • - Few along western segment of Koksneset fault • - Most on NW-SE striking transfer structures in Jan Mayen Platform, probably reactivated as oblique normal faults with right-lateral strike-slip component • - Still significant activity along the ruptured eastern segment of the Koksneset Fault • This event, together with event in 1988, provides evidence of where and how often the tectonic stresses are released.

21. Final remarks • This recent event sheds light to the tectonic processes acting on an area where a fracture zone and a mid-oceanic ridge interact closely • There are a number of remaining issues with regard to the influence of magmatic processes to tectonic events and vice versa. In this respect the Jan Mayen Platform represents an important brick in the processes acting simultaneously in a ridge-fracture zone interaction • The transition from ridge-perpendicular spreading at the Jan Mayen Platform and the JMFZ to oblique spreading along the Mohns ridge in the North poses major challenges in understanding the magmatic and tectonic processes