Open AccessSeismic attenuation in the continental crust SW of England
Author(s) -
Scheirer Daniel S.,
Hobbs Richard W.
Publication year - 1990
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 - 10.1111/j.1365-246x.1990.tb01789.x
Subject(s) - geology , crust , batholith , attenuation , seismology , continental crust , amplitude , upper crust , sedimentary rock , reflection (computer programming) , geophysics , geochemistry , tectonics , programming language , physics , quantum mechanics , computer science , optics
SUMMARY Significant variability in crustal attenuation exists off England's SW coast as shown by BIRPS deep seismic reflection lines. The presence of the thick Cornubian Batholith with no sedimentary cover, acting as a low‐attenuating region compared to normal upper crust with about 300 m of sedimentary cover, can account for the observed differences in the strength of signal returning from the lower crust. Application of the spectral amplitude ratio method to determine the effective quality factor, Q , of the lower crust beneath the granite yields a value of 400 ± 200. A modification of the spectral amplitude ratio method to measure relative Q 's at different locations indicates that the average Q of the upper and middle crust containing the granite is twice that elsewhere. Although the hypothesis that the lower crustal composition differs significantly beneath the granite cannot be ruled out, geological and seismic observations suggest that differential attenuation is the main factor causing variation in the observed reflectivity. Thus, thick granites act as low‐attenuating ‘windows’ to the lower crust.