Geology Reference
In-Depth Information
Zone:
H
I
J
K
L
M
R(km): 1.53
2.61
4.47
6.65
9.9
14.7
21.9
N:
12
12
16
16
16
16
1
32
42
72
88
101
125
2
46
60
101
124
148
182
3
56
74
125
153
186
225
4
65
85
144
176
213
262
5
73
95
161
197
239
291
6
80
104
176
216
261
319
7
86
112
191
233
282
346
8
92
120
204
249
303
370
9
96
127
216
264
322
391
10
103
134
228
278
338
413
20
146
190
322
394
479
586
30
179
233
396
483
587
717
40
206
269
457
557
679
828
50
231
301
511
624
759
926
60
253
330
561
683
832
1015
70
274
357
606
738
899
1097
80
293
382
648
790
962
1173
90
311
405
688
838
1020
1244
100
328
427
726
884
1076
1312
Effect (µGal):
Height differences (metres)
These tables list the exact height differences that, assuming a density of
2.0 Mg m
-3
, will produce the tabulated terrain effects. Thus a height dif-
ference of 32 m between the gravity station elevation and the average to-
pographic level in one compartment of Zone E (between 170 and 390 m
from the gravity station) would be associated with a terrain effect of about
18 µGal. Most commercial gravity meters have sensitivities of only 10 µGal,
but estimates to 1 µGal are used in the tabulation for small elevation dif-
ferences to avoid the accumulation of 'rounding off' errors when summing
the contributions from large numbers of compartments. For larger eleva-
tion differences, these levels of accuracy are not obtainable using Hammer
charts.
