Transcript Slide 1
Earthquakes & seismicity in Iceland: a tectonic saga Iceland Seminar Marianne Karplus 6 March 2009 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? Earthquakes 1994-2004 Tjornes Fracture Zone plume trace @ 300-400 km depth South Iceland Seismic Zone Vogfjord et al., 2008 South Iceland Seismic Zone Bergerat & Angelier, 2008 29 May 2008 Earthquake Mw=6.2, 15:46, depth 10 km USGS MSNBC South Iceland Seismic Zone Bergerat & Angelier, 2008 Why is the motion left lateral (sinistral)? June 2000 Earthquakes, M6.5 Sigurjon et al., 2003 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 Maturation of a transform zone IMMATURE MATURE 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 “Revelation in an asphalted car park” Angelier & Bergerat, 2002 Tjornes Fracture Zone Bergerat & Angelier, 2007 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–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 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