Seismicity of Iceland
description
Transcript of Seismicity of Iceland
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