Jökull - 01.12.1980, Page 49

TABLE 1.
Mean and standard deviation for various parameters. N is number of measurements, X
is arithmetic mean and S.D. is standard deviation. — Meðalgildi og staðalfrávik nokkurra
mœlistærða. N er fjöldi mælinga, X er meðalgildi og S.D. er staðalfrávik.
N X S.D.
Azimuth angle of fractures
Azimuth angle of fractures
Width in all points of measurements
Maximum width of fractures
Throw on faults
Maximum throw on fractures
Maximum throw on faults
Length of fractures
141 54.22° 16.49°
120 55.38° 17.87°
1076 0.61 m 1.05 m
120 1.00 - 1.30 -
34 2.31 - 2.79 -
141 1.16 - 2.48 -
34 4.66 - 2.93 -
120 611.03 -
marized in Table 1 and Table 2, and I refer to
them for accurate figures of the results dis-
cussed below.
TABLE 2.
Correlation between various parameters.
The values given are for the linear correlation
coefficient (r). — Samband nokkurra mælistærða.
Gildin í töflunm eru fyrir línulega fylgnistuðulinn
(r).
A B C
1 0.65 0.62
2 -0.04 -0.10 -0.09
3 0.46
4 0.34
5 0.64
1. Ma.ximum width of fractures
2. Azimuth angle of fractures
3. Mean width of fractures
4. Mean throw on faults
5. Maximum throw on faults
A. Length of fractures
B. Maximum throw on fractures
C. Mean width of faults
Orientation of fractures
Mean orientation of the fractures is 54°,
referring to the azimuth angle. There are,
however, only 120 fractures that do not go
beyond the mapped area, and their mean is
about 55°. I also considered the effect of
length on the orientation^nd it turned out to
be insignificant. As always, when speaking
about orientation, I am referring to the linear
orientation between the ends of the fracture.
The histogram in Fig. 5 shows the distribution
of the orientation of all the fractures, and Fig.
6 for fractures longer than 200 m. The dis-
tribution follows well the normal curve, as
could be expected (Krumbein and Graybill 1965).
The standard deviation is only about 17°.
This of course means that most of the fractures
have an orientation that is similar to the mean
orientation.
The histogram in Fig. 5 is not markedly
different from the one in Fig. 6. As the shorter
fractures, i.e. those equal to or less than 200 m,
are likely to be the youngest in the area (see
the section on the development of the frac-
tures), we can infer that the stress field has not
changed notably with time. Also, there is
nothing to indicate that more than one frac-
ture system exists in this area.
Obviously, the shape of the histograms
JÖKULL 30. ÁR 47