Seismicity of Iceland
Dr. Benedikt Halldorsson
Earthquake Occurrence in Iceland
• Overview
– Tectonics
– Interplate Earthquakes
• Transform Zones
– South Iceland Seismic Zone
– Tjörnes Fracture Zone (North Iceland Seismic Zone)
• Volcanic Zones
– Reykjanes Peninsula
– Hengill Triple-junction
– Eastern Volcanic Zone
– Intraplate Earthquakes
– Induced earthquakes
– Earthquake hazard map
UPStrat-MAFA 3rd General Meeting 23-26 July 2013, Selfoss, Iceland
Iceland and Plate tectonics
• Horizontal motion of plates
UPStrat-MAFA 3rd General Meeting 23-26 July 2013, Selfoss, Iceland
Steve Gao
Iceland and Plume tectonics
• Large scale vertical mantle plume motions
• Hot-spots are one manifestation of plume tectonics
USGS
UPStrat-MAFA 3rd General Meeting 23-26 July 2013, Selfoss, Iceland
Tectonics of Iceland: Combination of plate and plume tectonics
The “Icelandic Mantle Plume”
(Dr Dietmar Müller, University of Sydney)
Lundin & Dore (2004)
UPStrat-MAFA 3rd General Meeting 23-26 July 2013, Selfoss, Iceland
Tectonics of Iceland: Combination of plate and plume tectonics
• Mid-Atlantic Ridge of
tectonic extension between
the North American and
Eurasian Plates.
– RR=Reykjanes Ridge
– KR=Kolbeinsey Ridge
• In Iceland the interplay
between the tectonic
extension and mantle
plume define the
geodynamics
– Including volcanic and
earthquake occurrence
(Maclennam, 2001; Kaban et al., 2002)
UPStrat-MAFA 3rd General Meeting 23-26 July 2013, Selfoss, Iceland
Topography of Iceland
Björnsson & Palsson (2008)
UPStrat-MAFA 3rd General Meeting 23-26 July 2013, Selfoss, Iceland
Volcanic Systems and Earthquake Epicentres in Iceland
• Red dots = earthquake
epicentres 1994-2005
• Volcanic systems
• Black circles =
central volcanoes
• Yellow regions =
fissure swarms
• White regions =
glaciers
Guðmundsson (2001)
UPStrat-MAFA 3rd General Meeting 23-26 July 2013, Selfoss, Iceland
Present-Day Geodynamics of Iceland
• Average horizontal
velocities from GPS
measurements
– Green=NS-component
– Red = West component
– Blue= East component
• Defines the Present-Day
Rift Axis of the MidAtlantic Ridge in Iceland
Sigbjörnsson et al., 2006
UPStrat-MAFA 3rd General Meeting 23-26 July 2013, Selfoss, Iceland
Main tectonic structures and
earthquake epicentres
UPStrat-MAFA 3rd General Meeting 23-26 July 2013, Selfoss, Iceland
Simplified Geological Map of Iceland
Guðmundsson et al (2008)
UPStrat-MAFA 3rd General Meeting 23-26 July 2013, Selfoss, Iceland
Population Density in Iceland
Guðmundsson et al (2008)
UPStrat-MAFA 3rd General Meeting 23-26 July 2013, Selfoss, Iceland
The Icelandic Strong-motion Network
UPStrat-MAFA 3rd General Meeting 23-26 July 2013, Selfoss, Iceland
The South Iceland Seismic Zone
• Strong-motion stations in South Iceland
– Monitor ground movements and building response in the
region
UPStrat-MAFA 3rd General Meeting 23-26 July 2013, Selfoss, Iceland
Seismicity in the South Iceland Seismic Zone
[Einarsson, et al.]
Stefansson et al. (2006)
UPStrat-MAFA 3rd General Meeting 23-26 July 2013, Selfoss, Iceland
The Tjörnes Fracture Zone
(North Iceland Seismic Zone)
• Strong-motion stations in North Iceland
– The Tjörnes Fracture Zone is largely offshore
UPStrat-MAFA 3rd General Meeting 23-26 July 2013, Selfoss, Iceland
Seismicity in the Tjörnes Fracture Zone
• Recent strong historical
earthquakes (Green stars)
• Microearthquake
epicentres 1994-2012
(Black dots)
• Volcanic systems
• Central volcanoes (Black
circles)
• Fissure swarms (red
shaded regions)
• Rift axis (red dashed lines)
and direction of rifting
7.0
6.2
7.0
6.5
6.5
7.0
6.2
6.3
6.5
IMO (2012)
UPStrat-MAFA 3rd General Meeting 23-26 July 2013, Selfoss, Iceland
Ongoing earthquake sequence since 2012 in the Tjörnes
Fracture Zone
• Activity on the two major
structures of the TFZ, and
the extension ridge
• Largest events so far are
M5.5 and M5.6
• Measured by the new
strong-motion array in
Husavik, North Iceland
IMO (2013)
UPStrat-MAFA 3rd General Meeting 23-26 July 2013, Selfoss, Iceland
Seismicity in the Reykjanes Peninsula and the Hengill Triple
Junction
• Reykjanes Peninsula
– Narrow seismic zone
with shallow focus
earthquakes
– Normal faulting
South Iceland Seismic Zone
• Hengill
Reykjanes Peninsula
– Triple junction between
the Reykjanes Volcanic
Zone, The Western
Volcanic Zone, and
the South Iceland Seismic Zone.
– Seismicity of the Hengill volcanic system, normal faulting and
seismicity associated with geothermal activity
UPStrat-MAFA 3rd General Meeting 23-26 July 2013, Selfoss, Iceland
Volcanic Earthquakes in Iceland
• Rifting structures mostly aseismic except during eruptions
• Spatial clustering of epicenters – central volcanoes
• Primary classes of seismicity of the volcanic zones
–
–
–
–
–
Rifting earthquakes
Inflation earthquakes
Deflation earthquakes
Intrusion tremors
Eruption tremors
• Relatively smaller magnitudes than in the transform zones
UPStrat-MAFA 3rd General Meeting 23-26 July 2013, Selfoss, Iceland
Intraplate Earthquakes in Iceland
• Very rare events
• Primarily two cases
– Earthquakes in west Iceland
•
•
•
•
Borgarfjordur events of 1974
Largest magnitude was 6
No apparent single fault
Normal faulting
– Earthquakes on the insular shelf off Eastern Iceland
• Most located near shelf-edge
UPStrat-MAFA 3rd General Meeting 23-26 July 2013, Selfoss, Iceland
Induced Seismicity due to Fluid Injection
Hellisheidi Geothermal Power Plant, Southwest Iceland
Epicenters of induced earthquakes due
to fluid injection at Hellisheiði Power
Plant (45 days)
Station locations of the ICEARRAY I in
Hveragerði, 11 km away from the Power
Plant
• The induced seismicity
culminated in two ML 3.8
earthquakes on 15 October
2011
Halldorsson et al. (2012)
UPStrat-MAFA 3rd General Meeting 23-26 July 2013, Selfoss, Iceland
Earthquake Hazard in Iceland
10% probability in 50 years
of exceeding the specified
Peak Ground Acceleration
We are here!
(Solnes, Sigbjörnsson & Elíasson, 2004)
UPStrat-MAFA 3rd General Meeting 23-26 July 2013, Selfoss, Iceland
Summary
• Iceland is one of the most active countries in the world in
terms of seismicity and volcanism
• Its seismicity is caused by a complex interaction between the
tectonics and volcanism of Iceland
– The two having different geodynamics and manifestation
• The largest earthquakes in Iceland occur in the two transform
zones in the south and north, respectively
– Style of faulting depends on the development of the fault lineament
– The SISZ exhibits “bookshelf tectonics”
• The SISZ constitutes a unique natural field laboratory for the
study of earthquakes, their strong-motions and their effects
on the built environment
UPStrat-MAFA 3rd General Meeting 23-26 July 2013, Selfoss, Iceland