The lithosphere and asthenosphere of the Iceland hotspot from surface waves

• Published in: Biogeosciences
• Main Authors: Bjarnason, Ingi Þorleifur, Schmeling, Harro
• Other Authors: Raunvísindastofnun (HÍ), Science Institute (UI), Verkfræði- og náttúruvísindasvið (HÍ), School of Engineering and Natural Sciences (UI), Háskóli Íslands, University of Iceland
• Format: Article in Journal/Newspaper
• Language: English
• Published: Oxford University Press (OUP) 2009
• Subjects: Surface waves and free oscillations; Seismic anisotropy; Mid-ocean ridge processes; Hotspots; Crustal structure; Atlantic Ocean; Jarðeðlisfræði; Eldvirkni; Jarðmöttull; Jarðskorpa; Bylgjufræði; Atlantshaf; Iceland
• Online Access: https://hdl.handle.net/20.500.11815/503; https://doi.org/10.1111/j.1365-246X.2009.04155.x

1-D models were calculated for the velocity of shear waves, polarized vertically (SV) and horizontally (SH) from dispersed Rayleigh and Love surface waves. These had been recorded in Iceland by the ICEMELT broad-band seismic network, with about half of the waves coming from near-distance earthquakes (≤1000 km). The analysis included unusually short periods, as brief as 5.0 s, and periods ranging up to 93 s. The Icelandic crust was revealed to have two basic layers: first, the upper and middle crust, which were largely detected as one layer, and second the layer of the lower crust. The half of Iceland surveyed had a weighted average crustal thickness of 25–26 km, less than previously estimated. It is under East and East Central Iceland that the crust is thickest, averaging 29–32 ± 3 km, and under the western margin of the West Fjords, 29 ± 2 km. The thinnest parts of the crust lie in West Central Iceland, 19 ± 1 km, and in the West Volcanic (or Rift) Zone, 19[+6/−1] km. This study examined how thicker crust away from the rift zone can be fitted with dynamic crust formation models. Possible explanations for different thicknesses include both crustal squeezing flow and imbalances between widths of the volcanic accretion and extensional stretching zones. The crust has highly anisotropic zones, with differences of up to 20 per cent between SV and SH velocities. Under rift zones, the lower crust is characterized by low velocities and, at depths of 8–18 km, by a channel with yet lower velocities. The lowest shear velocity in this channel is 5–9 per cent less than in the standard Icelandic velocity model. The thinnest lithosphere, 20 ± 2 km, lies under the East Central and North Volcanic Zones, where it extends up into the crust, while the thickest lithosphere is under East Iceland and the east shelf, nowhere less than 100 ± 20 km. This substantial contrast in lithosphere thickness of some 80 km occurs within a lateral distance of 100–150 km, implying an age unconformity at depth of several tens of millions of years. ...