Seismicity of Iceland

Dr. Benedikt Halldorsson

UPStrat-MAFA 3rd General Meeting 23-26 July 2013, Selfoss, Iceland

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

Steve Gao

UPStrat-MAFA 3rd General Meeting 23-26 July 2013, Selfoss, Iceland

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 Mid-Atlantic 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 IcelandMonitor ground movements and building response in the

region

UPStrat-MAFA 3rd General Meeting 23-26 July 2013, Selfoss, Iceland

[Einarsson, et al.]

Seismicity in the South Iceland Seismic Zone

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 IcelandThe 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

IMO (2012)

6.5

6.57.0

6.5

6.2

7.0

6.3

7.0

6.2

UPStrat-MAFA 3rd General Meeting 23-26 July 2013, Selfoss, Iceland

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)

Ongoing earthquake sequence since 2012 in the Tjörnes Fracture Zone

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

Hengill Triple junction between

the Reykjanes VolcanicZone, The WesternVolcanic Zone, andthe South Iceland Seismic Zone.

Seismicity of the Hengill volcanic system, normal faulting and seismicity associated with geothermal activity

Reykjanes Peninsula

South Iceland Seismic Zone

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 InjectionHellisheidi 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

(Solnes, Sigbjörnsson & Elíasson, 2004)

We are here!

10% probability in 50 years of exceeding the specified Peak Ground Acceleration

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