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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?
Vogfjord et al., 2008
Tjornes Fracture Zone
Earthquakes 1994-2004
plume trace @ 300-400 km depth
South Iceland Seismic Zone
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
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
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
Húsavík–FlateyFault (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
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