Abstract

Q was determined for the southern Norway region using short-period data from local events. The spectral ratio and the coda decay method were used to determine Q as a function of frequency for P, S, and coda waves, respectively. Q(f) was generally found to fit the relationship Q = Qofm where f is the frequency and Qo and m constants. The following results were obtained:

Q at 10 Hz window length 
Qc = 55f1.15 780 20 sec 
Qc = 75f1.15 1060 30 sec 
Qc = 120f1.09 1430 40 sec 
Qp = 121f0.89 940 5 sec 
Qs = 127f1.08 1530 5 sec 
Q at 10 Hz window length 
Qc = 55f1.15 780 20 sec 
Qc = 75f1.15 1060 30 sec 
Qc = 120f1.09 1430 40 sec 
Qp = 121f0.89 940 5 sec 
Qs = 127f1.08 1530 5 sec 

where Qc, Qp, and Qs are coda Q, Q of P waves, and Q of S waves, respectively. There is a good agreement between coda Q and spectral ratio Qs values, which supports the hypothesis that coda waves are backscattered S waves. The increase in coda Q as a function of window length is thought to reflect an increase of Q with depth, because coda waves for a longer time window will sample deeper parts of the crust. At higher frequencies (12 to 15 Hz), our results are quite similar to what has been found for the Canadian Shield area, but with a much stronger frequency dependence. This could be interpreted in terms of a stronger presence of scatterers in southern Norway as compared to the Canadian Shield.

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