1. Earthquakes & seismicity in Iceland: a tectonic saga Iceland Seminar Marianne Karplus 6 March 2009

2. Today’s itinerary Where are the earthquakes? How big? How many? Why do they concentrate in certain areas? What is the sense of motion on the faults? What is there to see in the major seismic zones? What does seismicity tell us about the tectonics?

3. Vogfjord et al., 2008 Tjornes Fracture Zone Earthquakes 1994-2004 plume trace @ 300-400 km depth South Iceland Seismic Zone

4. Bergerat & Angelier, 2008

5. 29 May 2008 Earthquake M w =6.2, 15:46, depth 10 km MSNBC USGS

6. South Iceland Seismic Zone Bergerat & Angelier, 2008

7. Why is the motion left lateral (sinistral)?

8. Sigurjon et al., 2003 June 2000 Earthquakes, M6.5

9. South Iceland Seismic Zone East-West trending active transform zone Relatively immature transform zone ~ 2-3 Ma E-W LEFT LATERAL transform faults N-S RIGHT LATERAL transform faults Connects West & East Volcanic Zones Angelier et al., 2008

10. Maturation of a transform zone Angelier et al., 2008 IMMATURE MATURE

11. Fault patterns at regional & local scales Oblique aerial photo of typical N-S trending right-lateral fault Segmentation & en echelon pattern with push-up structures Outcrop is a typical push-up structure and individual fracture Bergerat & Angelier, 2008

12. “Revelation in an asphalted car park” Angelier & Bergerat, 2002

13. Tjornes Fracture Zone Bergerat & Angelier, 2007

14. Tjornes Fracture Zone Three tectonic lines trend parallel to the WNW-ESE transform zone More mature transform zone ~ 8-8.5 Ma Has featured > M6.0 earthquakes in last 100 yrs Parts of seismic zones offshore  tsunami hazard Connects North Volcanic Zone & Kolbeinsey Ridge Some extension near transform trend – “earthquake lake” Faults more tightly localized Geometrical fault pattern more complex

15. Húsavík–Flatey Fault (HFF) – morphology 25 km long feature on Tjornes peninsula Vertical throw ~ 1 km Lateral throw ~ 60 km Detail of Botnsvatn pull-apart Angelier et al., 2008

16. Broad features of Iceland seismicity Areas connecting ridges are seismically active – transform zones Some normal/extensional faulting too Several > M6.0 earthquakes per century – Mostly strike-slip – Variable orientations of slip Quakes accommodate relative motion of 2 plates South Iceland Seismic Zone –Less mature than TFZ –More diffuse shear zone –Simpler stress pattern