Rit (Vísindafélag Íslendinga) - 01.06.1971, Side 26

26
GUÐMUNDUR PÁLMASON
the average value given above, for calculating delay times for the
P3-wave.
5.3. S-wave velocities and Poisson’s ratio.
Average values of S-wave velocities have heen computed in the
same way as was done for the P-wave velocities. The results are
shown in the following table.
Table 5.4.
Layer S-velocity km/sec s km/se c n
1 2.34 ± 0.03 0.12 22
2 2.78 ± 0.02 0.13 32
3 3.53 ± 0.02 0.13 34
In each case, where hoth P- and S-wave velocities were deter-
mined, the value of Poisson’s ratio has been calculated. Average
values of this quantity are given below.
Table 5.5.
Layer Poisson’s ratio S n
1 0.270 ± 0.006 0.027 22
2 0.278 ± 0.003 0.014 31
3 0.269 ± 0.004 0.025 35
No attempt has been made to study S-waves from layer 4, although
such waves appear to be present on some of the longer profiles, e.g.
L1. A closer study on a larger number of profiles would be required
to determine Poisson’s ratio for layer 4.
5.4. Average thickness of layers.
It is perhaps of some interest to calculate “average” values of
layer thicknesses from the data in Tables 5.1-5.2 and those given by
Pálmason (1963), where the layer boundaries are assumed to be
horizontal under each profile. The variations in layer thickness are,
however, very real and show a systematic variation geographically.
Some of the layers are not found in some areas, such as layer 2 on
the Reykjanes peninsula and layer 0 outside the Neovolcanic zone.
The depth variations to the various layers are best described in terms
of the delay times as will be done in later sections.