Open AccessTransition zone structure in a tectonically inactive area: 410 and 660 km discontinuity properties under the northern North Sea
Author(s) -
Helffrich George,
Asencio Eugenio,
Knapp Jim,
Owens Tom
Publication year - 2003
Publication title -
geophysical journal international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0956-540X
DOI - 10.1046/j.1365-246x.2003.02036.x
Subject(s) - discontinuity (linguistics) , geology , receiver function , transition zone , volcanism , subduction , seismology , mantle (geology) , amplitude , seismometer , plume , attenuation , mantle plume , geophysics , tectonics , lithosphere , meteorology , mathematical analysis , physics , mathematics , quantum mechanics , optics
SUMMARY We report results from a year‐long deployment of broad‐band seismometers in Scotland to study the mantle structure in the northern United Kingdom. The region is tectonically inactive and its underlying mantle transition zone should not show unusual structure due to thermal perturbations caused by Cenozoic subduction or plume‐related volcanism. The estimated 410 and 660 km discontinuity depths, estimated by receiver function stacking, are 414 ± 5 and 655 ± 14 km , typical of average worldwide values. There is no evidence for a discontinuity at 520 km. The 660 km discontinuity conversion is weaker than global Earth models predict by factors of 1.65–2.97, which is significant given amplitude measurement uncertainties. Either significant attenuation below 410 km or regional, non‐thermal variations in 660 km discontinuity properties that decrease its velocity and density jumps to 1.9 per cent Δ V p , 4.8 per cent Δ V s and 4.8 per cent Δρ , or that broaden it to 13–35 km width could account for the lower than expected amplitudes. Lateral variations in transition zone water content around the 660 km discontinuity may be responsible for the broadening.