ISSN:
1365-246X
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Geosciences
Notes:
Very little seismic attenuation occurs in the mid to lower crust of south-west Iceland. The lowest path-averaged quality factor for a wave turning in the mid to lower crust (12–20 km) is QP= 110 for P waves and QS= 250 for S waves, with most of the data having higher values, typically QP= 200–300 and QS= 400–600. Attenuation estimates based on a 1-D, layered inversion give correspondingly high values, QP 〉 800 and QS= 800–2000. These Q values are inconsistent with thermal models that predict a broad (100 km wide) region of above-solidus temperatures centred on the volcanic zones. The observed attenuation implies an upper limit for mid to lower crustal temperature in the 700–775°C range (assuming a gabbroic lithology). Much higher attenuation (QP= 60, QS= 100) occurs in the uppermost 4 km of crust. This is most likely apparent attenuation caused by strong near-surface seismic heterogeneity, resulting from fissures, faults and extreme changes in porosity (up to 20–30 per cent). The quality factor of the near-surface layer varies regionally, and is lower in volcanic zones than in either the Reykjanes Peninsula or the South Iceland Lowland.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1365-246X.1995.tb03545.x
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